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"CW" no adddress@spam free.com wrote in message ...
They don't but if you go by the advice you generally get on the antenna group, you run an unshielded lead in (part of the antenna) right into the shack (big noise source). When I made my prior comments about the lack of consideration given to receive antenna, I was referring to the antenna group. I didn't realize that the message was cross posted. It just amazes me that they will debate a transmitting antenna to minute detail but receiving antennas deserve no consideration other than a random piece of wire thrown into a tree. Despite their often one sidedness I have learned a great deal from them and mean no disrespect. CW, That is 'why' I set-up the "Shortwave Listeners (SWL) AM/FM Antennas" eGroup on YAHOO ! SWL-ANT= http://groups.yahoo.com/group/Shortwave-SWL-Antenna/ Most HAM are concerned about getting the most power transfer into the Antenna and the greatest Signal Output from the Antenna. This may not result in the best receiving antenna. A better SWL Receive ONLY Antenna is usually a result of a Clean 'outside' Signal with a "Low Noise" factor. Yes the topic is SWL Receive ONLY Antennas. SWL-ANT= http://groups.yahoo.com/group/Shortwave-SWL-Antenna/ iane ~ RHF .. |
= = = Richard Clark wrote in message
= = = . .. On Sun, 27 Jun 2004 19:55:58 -0700, "CW" no adddress@spam free.com wrote: When I made my prior comments about the lack of consideration given to receive antenna, I was referring to the antenna group. I didn't realize that the message was cross posted. It just amazes me that they will debate a transmitting antenna to minute detail but receiving antennas deserve no consideration other than a random piece of wire thrown into a tree. Hi OM, As generalizations go, this one falls short with them all. We here at rec.radio.amateur.antenna often recite the credo that "reciprocity rules." This means that all considerations given to a transmitting antenna are equally applied to receiving antennas. However, I am sure you are responding to the disparity in coverage between receiving and transmitting antennas - and this is for good reason. Reception and Transmission are NOT reciprocal operations. A receiver has far more latitude to accomplish its goal than does a transmitter. Unless you have an abysmal receiver poorly connected to an inadequate whip, the stock receiver with a simple length of wire is often very close to doing a good job. If the receiver suffers from any of a multitude of issues, there is generally a solution that answers the problem specifically. About the only thing you can do for the transmitter is to turn up the power, or lower the transmission loss. It stands to reason that our focus is on optimizing the loss side of the balance ledger. Returning to the credo of "reciprocity rules," any gain to the advantage of a transmitter is enjoyed by the receiver and the SWLer stands the same advantage. But if that advantage is measured at 3dB, this has the significance of 50W in 100W compared to the SWL S-Meter change from S5 to S6 (BFD). Even though it is the same 3dB, there is the illusion of perspective (my 50W compared to your 5µV). If the SW station is buried in S9 noise, then this is not an antenna problem (unless you can null the noise out through careful lobe positioning). Filtering and/or DSP stand to answer the problem, but these are obviously not remedies to transmission issues. There is another thread discussing the goal of constructing a small loop for 80M reception (and how well 5 turns might achieve some benefit). The same issues of loss prevail for the comparison of Radiation Resistance to Ohmic Resistance for a 1 Meter loop. The loop Rr is in the thousandths of an Ohm and about on par for a small wire's Ohmic loss. There's that 3dB again and what concerns the transmission efficiency is far easier to tolerate with the receiver and its surplus of gain. If the SWLer pays attention to this issue as it concerns the transmission problems, then that SWLer stands to gain in the efficiency returned. However, this is not to suggest that there is an actual need to obtain this efficiency; but if the SWLer mismanages the construction, the topic is discussed to the necessary depth to correct it. A simple basis of comparison will illustrate. Many SW radios have a ferrite stick antenna that will work with at least some stations (VOA, WWV, BBC and a host of others). Try transmitting through that same ferrite stick and it will be like trying to shout through a straw. Our only alternative is to add an amp, but the big KW is only going to render smoke. 73's Richard Clark, KB7QHC RC, In the same location using the same Antenna: 100uV of background noise being re-radiated by a Transmitting Antenna that is being powered at 50W or 100W is simply not an issue for the Amateur/HAM. - Background Noise is NOT an Issue when thinking of Transmitting Antennas that are Radiating Power in the Tens and Hundreds of Watts. - For the HAM Signal-to-Noise is NOT a Transmission Antenna Parameter. 100uV of background noise being received by a Receiving Antenna that is seeking a 25uV Signal is unacceptable for a SWLer. - Background Noise IS an Issue when thinking of Receiving Antennas that are 'acquiring' Radiated Power in the Milliwatts or micro-watts. - For the SWLer Signal-to-Noise IS a key Receiving Antenna Parameter. iane ~ RHF .. Shortwave Listeners (SWL) AM/FM Antennas eGroup on YAHOO ! SWL-ANTENNA= http://groups.yahoo.com/group/Shortwave-SWL-Antenna/ .. |
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On Tue, 29 Jun 2004 09:13:35 +0200, Mark1
wrote: Zeg hallo, dit is een Nederlandse nieuwsgroep hoor :-P probeer de vertaaldiensten van bable vissen bij http://babelfish.altavista.com/ 73's Richard Clark, KB7QHC |
Richard Clark had uiteengezet :
On Tue, 29 Jun 2004 09:13:35 +0200, Mark1 wrote: Zeg hallo, dit is een Nederlandse nieuwsgroep hoor :-P probeer de vertaaldiensten van bable vissen bij http://babelfish.altavista.com/ 73's Richard Clark, KB7QHC LOL, we zien hoe goed de vertaalmachine werkt (not) |
Op dinsdag 29-6-2004 krabbelde Mark1 op mijn schermpje
Richard Clark had uiteengezet : On Tue, 29 Jun 2004 09:13:35 +0200, Mark1 wrote: Zeg hallo, dit is een Nederlandse nieuwsgroep hoor :-P probeer de vertaaldiensten van bable vissen bij http://babelfish.altavista.com/ 73's Richard Clark, KB7QHC LOL, we zien hoe goed de vertaalmachine werkt (not) Dit even ter illustratie...Tis niet te lezen. Dergelijke voorbeelden van kleine lijnen die voor MF worden gebruikt zijn bewijspositief hoe armen een antenne kan zijn, en de de aanwinstenknop van rf doend herleven zijn meelijwekkende efficiency. Dit toont niet aan één of andere illusie van meerdere antenneontwerp ontvangt; eerder is het meer rook en spiegels als argument. Omkerend het argument, als u een volledige met maat antenne voor die band had, zou u slechts een van de loodglanskristal en kat bakkebaard nodig hebben om uw hoofdtelefoon aan te drijven hallo-z. Voor DX zou u slechts een $5 AF versterker nodig hebben. De kleinere antenne vergt duidelijk meer dollars besteed om debilities van de slechtere efficiency te compenseren. Het specious argument wordt gemaakt voor technisch uitgeput wie eerder een creditcard over de vertoningsteller dan bouwt hun eigen goedkope oplossing zou duwen. Neem eenvoudig hart dat dit niet een goedkoop schot, zijn er zo vele Hammen die don't weten welk eind van de soldeerbout om één van beiden op te nemen. -- Met vriendelijke groet, Gert-Jan Dam HF knutselhoekje: http://www.pg0g.net De nieuwsgroepronde Homepage: http://www.nieuwsgroepronde.tk http://members.hostedscripts.com/antispam.html |
'zou u slechts een van de loodglanskristal en kat bakkebaard nodig
hebben om uw hoofdtelefoon aan te drijven' rofl Mark Na rijp beraad schreef Gert-Jan Dam PG0G : Op dinsdag 29-6-2004 krabbelde Mark1 op mijn schermpje Richard Clark had uiteengezet : On Tue, 29 Jun 2004 09:13:35 +0200, Mark1 wrote: Zeg hallo, dit is een Nederlandse nieuwsgroep hoor :-P probeer de vertaaldiensten van bable vissen bij http://babelfish.altavista.com/ 73's Richard Clark, KB7QHC LOL, we zien hoe goed de vertaalmachine werkt (not) Dit even ter illustratie...Tis niet te lezen. Dergelijke voorbeelden van kleine lijnen die voor MF worden gebruikt zijn bewijspositief hoe armen een antenne kan zijn, en de de aanwinstenknop van rf doend herleven zijn meelijwekkende efficiency. Dit toont niet aan één of andere illusie van meerdere antenneontwerp ontvangt; eerder is het meer rook en spiegels als argument. Omkerend het argument, als u een volledige met maat antenne voor die band had, zou u slechts een van de loodglanskristal en kat bakkebaard nodig hebben om uw hoofdtelefoon aan te drijven hallo-z. Voor DX zou u slechts een $5 AF versterker nodig hebben. De kleinere antenne vergt duidelijk meer dollars besteed om debilities van de slechtere efficiency te compenseren. Het specious argument wordt gemaakt voor technisch uitgeput wie eerder een creditcard over de vertoningsteller dan bouwt hun eigen goedkope oplossing zou duwen. Neem eenvoudig hart dat dit niet een goedkoop schot, zijn er zo vele Hammen die don't weten welk eind van de soldeerbout om één van beiden op te nemen. |
Op dinsdag 29-6-2004 krabbelde Mark1 op mijn schermpje
'zou u slechts een van de loodglanskristal en kat bakkebaard nodig hebben om uw hoofdtelefoon aan te drijven' Ja haha. Lachen zo'n vertaal programma :D rofl Mark -- Met vriendelijke groet, Gert-Jan Dam HF knutselhoekje: http://www.pg0g.net De nieuwsgroepronde Homepage: http://www.nieuwsgroepronde.tk http://members.hostedscripts.com/antispam.html |
On Tue, 29 Jun 2004 11:46:03 +0200, Gert-Jan Dam PG0G
wrote: Dit even ter illustratie...Tis niet te lezen. Dergelijke voorbeelden van kleine lijnen die voor MF worden gebruikt zijn bewijspositief hoe armen een antenne kan zijn, en de de aanwinstenknop van rf doend herleven zijn meelijwekkende efficiency. Dit toont niet aan één of andere illusie van meerdere antenneontwerp ontvangt; eerder is het meer rook en spiegels als argument. Omkerend het argument, als u een volledige met maat antenne voor die band had, zou u slechts een van de loodglanskristal en kat bakkebaard nodig hebben om uw hoofdtelefoon aan te drijven hallo-z. Voor DX zou u slechts een $5 AF versterker nodig hebben. De kleinere antenne vergt duidelijk meer dollars besteed om debilities van de slechtere efficiency te compenseren. Het specious argument wordt gemaakt voor technisch uitgeput wie eerder een creditcard over de vertoningsteller dan bouwt hun eigen goedkope oplossing zou duwen. Neem eenvoudig hart dat dit niet een goedkoop schot, zijn er zo vele Hammen die don't weten welk eind van de soldeerbout om één van beiden op te nemen. Hi OM, Één of andere goede vertaling, slecht wat. Wat kwamen uit zeer goed zelfs daarna twee vertalingen. 73's Richard Clark, KB7QHC |
On Tue, 29 Jun 2004 16:14:57 +0200, Gert-Jan Dam PG0G
wrote: Op dinsdag 29-6-2004 krabbelde Mark1 op mijn schermpje 'zou u slechts een van de loodglanskristal en kat bakkebaard nodig hebben om uw hoofdtelefoon aan te drijven' Ja haha. Lachen zo'n vertaal programma :D rofl Mark Hi OM, het van het kattenbakkebaard en loodglans kristal is de oude componenten van de tijddetector. De bakkebaard van de kat is fijne draad. Het kristal van het loodglans is semiconducting mineraal (waar de draad raakt en contact met een oxyde opneemt). De twee componenten maken een diode. 73's Richard Clark, KB7QHC |
Op dinsdag 29-6-2004 krabbelde Richard Clark op mijn schermpje
On Tue, 29 Jun 2004 11:46:03 +0200, Gert-Jan Dam PG0G Één of andere goede vertaling, slecht wat. Wat kwamen uit zeer goed zelfs daarna twee vertalingen. Ik heb een willekeurig stuk vertaald. Dit kwam eruit en het is gewoon onleesbaar. 73's Richard Clark, KB7QHC -- Met vriendelijke groet, Gert-Jan Dam HF knutselhoekje: http://www.pg0g.net De nieuwsgroepronde Homepage: http://www.nieuwsgroepronde.tk http://members.hostedscripts.com/antispam.html |
On Tue, 29 Jun 2004 20:13:57 +0200, Gert-Jan Dam PG0G
wrote: Ik heb een willekeurig stuk vertaald. Dit kwam eruit en het is gewoon onleesbaar. Mijn fout toen. De kortere zinnen zijn nodig. |
Op dinsdag 29-6-2004 krabbelde Richard Clark op mijn schermpje
On Tue, 29 Jun 2004 16:14:57 +0200, Gert-Jan Dam PG0G het van het kattenbakkebaard en loodglans kristal is de oude componenten van de tijddetector. De bakkebaard van de kat is fijne draad. Het kristal van het loodglans is semiconducting mineraal (waar de draad raakt en contact met een oxyde opneemt). De twee componenten maken een diode. Ik zal eens van een bakkebaard van een kat en wat loodglans een diode maken hi. Sorry, _This_ is a Dutch newsgroup! 73's Richard Clark, KB7QHC -- Met vriendelijke groet, Gert-Jan Dam HF knutselhoekje: http://www.pg0g.net De nieuwsgroepronde Homepage: http://www.nieuwsgroepronde.tk http://members.hostedscripts.com/antispam.html |
On Tue, 29 Jun 2004 20:29:31 +0200, Gert-Jan Dam PG0G
wrote: Sorry, _This_ is a Dutch newsgroup! Of course it is: nl.radio.amateur This is an amateur antenna discussion. This discussion originated from this group (nl.radio.amateur). If this is a mistake, take it up with the original poster. 73's Richard Clark, KB7QHC |
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Richard Clark beweerde :
On Tue, 29 Jun 2004 16:14:57 +0200, Gert-Jan Dam PG0G wrote: Op dinsdag 29-6-2004 krabbelde Mark1 op mijn schermpje 'zou u slechts een van de loodglanskristal en kat bakkebaard nodig hebben om uw hoofdtelefoon aan te drijven' Ja haha. Lachen zo'n vertaal programma :D rofl Mark Hi OM, het van het kattenbakkebaard en loodglans kristal is de oude componenten van de tijddetector. De bakkebaard van de kat is fijne draad. Het kristal van het loodglans is semiconducting mineraal (waar de draad raakt en contact met een oxyde opneemt). De twee componenten maken een diode. 73's Richard Clark, KB7QHC Translation, : it from it cat-sideburn and leadshine cristal is the old components of the timedetector. The sideburn of the cat is fine thread. And so on. So pse remove this group from future postings. |
Richard Clark wrote:
Antennas have no capacity to reduce Signal to Noise ratios except by virtue of narrowing lobes to eliminate noise by placing it in a null (if that is in fact a viable option either in the sense of having a null, or having a null to a noise source that is not on the same meridian as the signal of interest). Not true. You are making the assumption that that the antenna only picks up radiated modes. Non-radiated electromagnetic modes are also troublesome, particularly common mode on the transmission line. This tends to be the way that locally generated noise from household gadgets gets into an antenna system. Consider a lamp dimmer that generates 10 mW of RFI, which rides out in common mode on the mains, finds its way to the power cord of your transceiver, rides out on the feedline to the antenna, and then couples back through differential mode to your receiver input. That's not a very efficient coupling path, so suppose it has a loss of 60 dB. You'll still get 10 nW to the receiver. This is a lot: even if it's spread over 30 MHz, it's still 10 uV in a 6 kHz channel. That's S6 on my Drake R-8, a very serious quantity of noise. On the other hand, if your transmitter puts out 1 kW, 60 dB of loss means it only delivers 1 mW of RF to the dimmer, an amount unlikely to interfere with its operation. Reciprocity does not mean *consequences* are symmetrical. To this point, you have not offered any particularly receive dominated issue that is not already a heavily trafficked topic with transmission antennas. A deep, steerable null can be extremely useful for reception, but its not generally useful for transmission. In fact, the presumption there are unique reception antennas that are more suitable than their transmission cousins is simply the artifice of my aforementioned advantage of the RF Gain control. It has been long established (through the simple act of purchase power) that receivers have far more gain available than needed except for the worst of antenna designs (and that has to be an exceptionally vile design). Such examples of small loops used for MF are proof positive how poor an antenna can be, and the RF gain knob resurrecting its pitiful efficiency. But for MWDX reception, efficiency simply isn't an important virtue. Gain is cheap. What matters is the steerable nulls. An efficient *steerable* MW antenna is enormous and expensive. This does NOT demonstrate some illusion of superior receive antenna design; rather it is more smoke and mirrors as an argument. Inverting the argument, if you had a full sized antenna for that band, you would only need a galena crystal and cat whisker to power your hi-Z headset. For DX you would only need a $5 AF amplifier. The smaller antenna clearly needs more dollars expended to offset the debilities of the poorer efficiency. Sensitivity is the cheapest, easiest virtue to put into a receiver. Essentially all modern receivers have plenty. Indeed, the cheap ones often overload when presented with an efficient antenna: you have to spend the dollars to be able to handle the big signals! Speaking of strawmen, have you ever actually tried DXing with a crystal radio? The specious argument is tailored for the technically effete who would rather push a credit card across the display counter than build their own cheap solution. Take heart that this not simply a cheap shot, there are as many Hams who don't know which end of the soldering iron to pick up either. I love designing and building antennas: applied physics is fun. But it's good engineering to go with the strengths of your technology. For my inverted-L's, I spend a little efficiency (4 dB or so) to get octaves of effective bandwidth, something that is perhaps of little use to hams, but is very useful to an SWL in conjunction with the frequency agility of a modern receiver. 4 dB of efficiency loss is of negligible consequence at HF and below if your receiver has a decent noise figure. I've never seen mention of this efficiency/bandwidth tradeoff in the ham literature, but it's not hard to find in the professional literature. For details of a specific calculation, see: http://anarc.org/naswa/badx/antennas/SWL_longwire.html -jpd |
pse remove the nl newsgroup from this discussion.
John Doty schreef op 29-6-04 : Richard Clark wrote: Antennas have no capacity to reduce Signal to Noise ratios except by virtue of narrowing lobes to eliminate noise by placing it in a null (if that is in fact a viable option either in the sense of having a null, or having a null to a noise source that is not on the same meridian as the signal of interest). Not true. You are making the assumption that that the antenna only picks up radiated modes. Non-radiated electromagnetic modes are also troublesome, particularly common mode on the transmission line. This tends to be the way that locally generated noise from household gadgets gets into an antenna system. Consider a lamp dimmer that generates 10 mW of RFI, which rides out in common mode on the mains, finds its way to the power cord of your transceiver, rides out on the feedline to the antenna, and then couples back through differential mode to your receiver input. That's not a very efficient coupling path, so suppose it has a loss of 60 dB. You'll still get 10 nW to the receiver. This is a lot: even if it's spread over 30 MHz, it's still 10 uV in a 6 kHz channel. That's S6 on my Drake R-8, a very serious quantity of noise. On the other hand, if your transmitter puts out 1 kW, 60 dB of loss means it only delivers 1 mW of RF to the dimmer, an amount unlikely to interfere with its operation. Reciprocity does not mean *consequences* are symmetrical. To this point, you have not offered any particularly receive dominated issue that is not already a heavily trafficked topic with transmission antennas. A deep, steerable null can be extremely useful for reception, but its not generally useful for transmission. In fact, the presumption there are unique reception antennas that are more suitable than their transmission cousins is simply the artifice of my aforementioned advantage of the RF Gain control. It has been long established (through the simple act of purchase power) that receivers have far more gain available than needed except for the worst of antenna designs (and that has to be an exceptionally vile design). Such examples of small loops used for MF are proof positive how poor an antenna can be, and the RF gain knob resurrecting its pitiful efficiency. But for MWDX reception, efficiency simply isn't an important virtue. Gain is cheap. What matters is the steerable nulls. An efficient *steerable* MW antenna is enormous and expensive. This does NOT demonstrate some illusion of superior receive antenna design; rather it is more smoke and mirrors as an argument. Inverting the argument, if you had a full sized antenna for that band, you would only need a galena crystal and cat whisker to power your hi-Z headset. For DX you would only need a $5 AF amplifier. The smaller antenna clearly needs more dollars expended to offset the debilities of the poorer efficiency. Sensitivity is the cheapest, easiest virtue to put into a receiver. Essentially all modern receivers have plenty. Indeed, the cheap ones often overload when presented with an efficient antenna: you have to spend the dollars to be able to handle the big signals! Speaking of strawmen, have you ever actually tried DXing with a crystal radio? The specious argument is tailored for the technically effete who would rather push a credit card across the display counter than build their own cheap solution. Take heart that this not simply a cheap shot, there are as many Hams who don't know which end of the soldering iron to pick up either. I love designing and building antennas: applied physics is fun. But it's good engineering to go with the strengths of your technology. For my inverted-L's, I spend a little efficiency (4 dB or so) to get octaves of effective bandwidth, something that is perhaps of little use to hams, but is very useful to an SWL in conjunction with the frequency agility of a modern receiver. 4 dB of efficiency loss is of negligible consequence at HF and below if your receiver has a decent noise figure. I've never seen mention of this efficiency/bandwidth tradeoff in the ham literature, but it's not hard to find in the professional literature. For details of a specific calculation, see: http://anarc.org/naswa/badx/antennas/SWL_longwire.html -jpd |
On Tue, 29 Jun 2004 15:34:42 -0600, John Doty
wrote: You are making the assumption that that the antenna only picks up radiated modes. I am making no such assumption and all following commentary does absolutely nothing to separate the concerns of SWLers from Ham activity. Non-radiated electromagnetic modes are also troublesome, particularly common mode on the transmission line. This tends to be the way that locally generated noise from household gadgets gets into an antenna system. Consider a lamp dimmer that generates 10 mW of RFI, which rides out in common mode on the mains, finds its way to the power cord of your transceiver, rides out on the feedline to the antenna, and then couples back through differential mode to your receiver input. That's not a very efficient coupling path, so suppose it has a loss of 60 dB. You'll still get 10 nW to the receiver. This is a lot: even if it's spread over 30 MHz, it's still 10 uV in a 6 kHz channel. That's S6 on my Drake R-8, a very serious quantity of noise. Let's work with exactly that scenario you offered. S6 (Calibrated) on my Drake TR-7 is -88dBm - so close to your 10µV to be indistinguishable. My TS-430 varies from -80dBm to -73dBm. There is no calibrated S-Meter for my DX-440, but for a $200 SW set, its sensitivity is -90dBm for a full scale meter indication (about 7dB range from top to bottom). All very well and good. Now if we regard this speculation of 10mW (it is, after all, the epitome of a wild ass guess, isn't it?); then, let's reverse engineer that 10nW product from 6kHz buckets over the range of 30MHz to find 50µW which is 23dB below the original power presumably suppressed 60dB. Well, I have either pencil-whipped you, or you me, or each other - the numbers don't add up. Hardly matters given the original specification had no basis in fact. However, if I return to the original "problem" of noise derived from household sources; then that is also something I have closely measured. Across time, frequency, antennas, and known noise sources I have found it as low as S1 for my longwire (an antenna supposedly unused by Hams) to as high as S7 (for that same longwire). My loops, dipoles and verticals hardly fell outside of this range to present any gilt-edge design. With every circuit in the house broken (operating battery power in the dark), average noise level was either S2 for a vertical, or S1 to S3 for a loop (rather upsetting the voodoo of loops being quiet and verticals being noisy). When I returned power to the house by stages, I insured every opportunity of injecting noise by setting dimmers to their worst position (about 50%). In the low bands, I suffered as much as S8 noise levels with an average of S5 when the house was full lit (also including fluorescents) and all noise sources adding to the cacophony of reception. This was for a loop antenna. On the other hand, if your transmitter puts out 1 kW, 60 dB of loss means it only delivers 1 mW of RF to the dimmer, an amount unlikely to interfere with its operation. Reciprocity does not mean *consequences* are symmetrical. This effect of reciprocity has been reported so frequently in this group so as to negate your premise. We have many queries for how to solve this problem. To this point, you have not offered any particularly receive dominated issue that is not already a heavily trafficked topic with transmission antennas. A deep, steerable null can be extremely useful for reception, but its not generally useful for transmission. This really goes off the deep edge. Barring loss introduced for the sake of jimmying the logic, transmitters AND receivers enjoy the GAIN derived from the introduction of a null not otherwise part of the characteristic. This is a commonplace of theory and practice. Where ever you can design or contribute to a null; then this must of necessity result in an increase in signal outside of its region. These are all commonplace observations discussed here that are observable for either Ham or SWL operations. There is NO differential offered in these observations that separate SWL from Ham activities. Such examples of small loops used for MF are proof positive how poor an antenna can be, and the RF gain knob resurrecting its pitiful efficiency. But for MWDX reception, efficiency simply isn't an important virtue. I believe I have said that at least 3 to 5 times already. Gain is cheap. What matters is the steerable nulls. An efficient *steerable* MW antenna is enormous and expensive. Who needs an efficient MW antenna? This does NOT demonstrate some illusion of superior receive antenna design; rather it is more smoke and mirrors as an argument. Inverting the argument, if you had a full sized antenna for that band, you would only need a galena crystal and cat whisker to power your hi-Z headset. For DX you would only need a $5 AF amplifier. The smaller antenna clearly needs more dollars expended to offset the debilities of the poorer efficiency. Sensitivity is the cheapest, easiest virtue to put into a receiver. Essentially all modern receivers have plenty. Indeed, the cheap ones often overload when presented with an efficient antenna: you have to spend the dollars to be able to handle the big signals! All of $20 if you have any technical capacity. Otherwise push the credit card across the display counter and spend as much as they can sell you. This argument is like driving your car into the shop to get the air changed in your tires every 100 miles. Again, front end overload is a very common complaint offered here by SWLers who are then advised in how to simply AND cheaply combat this problem. Speaking of strawmen, have you ever actually tried DXing with a crystal radio? Sure, what is so remarkable about that? Beyond this simple design, ever hear of a super-Regen receiver? You don't need to spend half a kilo-buck to get the same sensitivity and filtering is dirt cheap. How about Q-multipliers? All such topics barely spread the wallet as much as the illusion of more buttons make a better rig. I love designing and building antennas: applied physics is fun. But it's good engineering to go with the strengths of your technology. For my inverted-L's, I spend a little efficiency (4 dB or so) to get octaves of effective bandwidth, something that is perhaps of little use to hams, but is very useful to an SWL in conjunction with the frequency agility of a modern receiver. 4 dB of efficiency loss is of negligible consequence at HF and below if your receiver has a decent noise figure. As I pointed out to Yahoo, if you choose to cripple yourself, then slide on over to the shoulder and enjoy kicking up dust and rocks as you travel down the road. a 4dB loss for an inverted L (hardly a SW invention) is far too simple to remedy to make its suffering a boast of martyrdom. It is a strange argument to offer that you can't afford a $20 solution for your $500 set and $2 worth of wire. I've never seen mention of this efficiency/bandwidth tradeoff in the ham literature, You haven't looked. Either contrived, wholly fictional, or accurately represented, it is part of the stock in trade for selling antennas. In this group, I would wager its discussion consumes more bandwidth than bragging about how many QSL cards have been pasted to the wall. but it's not hard to find in the professional literature. For details of a specific calculation, see: http://anarc.org/naswa/badx/antennas/SWL_longwire.html -jpd It would do you well to note that this "professional" whom you rely upon, John Kraus, is one of the most notable Ham Radio Operators frequently acknowledged and referred to here. Do you or others have any actual differentiable discussion, or is this simply an outlet for appoligia for why it isn't worth the strain to lift a soldering iron when you can bench press a credit card? 73's Richard Clark, KB7QHC |
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Richard Clark wrote:
On Tue, 29 Jun 2004 15:34:42 -0600, John Doty wrote: You are making the assumption that that the antenna only picks up radiated modes. I am making no such assumption and all following commentary does absolutely nothing to separate the concerns of SWLers from Ham activity. Non-radiated electromagnetic modes are also troublesome, particularly common mode on the transmission line. This tends to be the way that locally generated noise from household gadgets gets into an antenna system. Consider a lamp dimmer that generates 10 mW of RFI, which rides out in common mode on the mains, finds its way to the power cord of your transceiver, rides out on the feedline to the antenna, and then couples back through differential mode to your receiver input. That's not a very efficient coupling path, so suppose it has a loss of 60 dB. You'll still get 10 nW to the receiver. This is a lot: even if it's spread over 30 MHz, it's still 10 uV in a 6 kHz channel. That's S6 on my Drake R-8, a very serious quantity of noise. Let's work with exactly that scenario you offered. S6 (Calibrated) on my Drake TR-7 is -88dBm - so close to your 10µV to be indistinguishable. My TS-430 varies from -80dBm to -73dBm. There is no calibrated S-Meter for my DX-440, but for a $200 SW set, its sensitivity is -90dBm for a full scale meter indication (about 7dB range from top to bottom). All very well and good. Now if we regard this speculation of 10mW (it is, after all, the epitome of a wild ass guess, isn't it?); then, let's reverse engineer that 10nW product from 6kHz buckets over the range of 30MHz to find 50µW which is 23dB below the original power presumably suppressed 60dB. Well, I have either pencil-whipped you, or you me, or each other - the numbers don't add up. 10 uV into 50 ohms is 2 pW, not 10 nW (E^2/R). 2 pW = -117 dBW = -87 dBm. Multiplying by 30000/6 = 5000 buckets makes 10 nW or -50 dBm. Cancel the assumed 60 dB loss and I get +10 dBm, or 10 mW. The numbers add up fine. However, if I return to the original "problem" of noise derived from household sources; then that is also something I have closely measured. Across time, frequency, antennas, and known noise sources I have found it as low as S1 for my longwire (an antenna supposedly unused by Hams) to as high as S7 (for that same longwire). My loops, dipoles and verticals hardly fell outside of this range to present any gilt-edge design. Just because you couldn't doesn't mean others can't. Look at the rest of the articles on the BADX site. Taking steps to minimize common mode coupling has worked very well for me, and many people tell me it works for them too. You might also find the articles at http://www.qsl.net/wa1ion/ interesting, especially the one entitled "Another Look at Noise Reducing Antennas". Mark's antenna designs are generally useless for transmitting, but they make superb MWDX receiving antennas. With every circuit in the house broken (operating battery power in the dark), average noise level was either S2 for a vertical, or S1 to S3 for a loop (rather upsetting the voodoo of loops being quiet and verticals being noisy). When I returned power to the house by stages, I insured every opportunity of injecting noise by setting dimmers to their worst position (about 50%). In the low bands, I suffered as much as S8 noise levels with an average of S5 when the house was full lit (also including fluorescents) and all noise sources adding to the cacophony of reception. This was for a loop antenna. On the other hand, if your transmitter puts out 1 kW, 60 dB of loss means it only delivers 1 mW of RF to the dimmer, an amount unlikely to interfere with its operation. Reciprocity does not mean *consequences* are symmetrical. This effect of reciprocity has been reported so frequently in this group so as to negate your premise. We have many queries for how to solve this problem. To this point, you have not offered any particularly receive dominated issue that is not already a heavily trafficked topic with transmission antennas. A deep, steerable null can be extremely useful for reception, but its not generally useful for transmission. This really goes off the deep edge. Barring loss introduced for the sake of jimmying the logic, transmitters AND receivers enjoy the GAIN derived from the introduction of a null not otherwise part of the characteristic. This is a commonplace of theory and practice. Where ever you can design or contribute to a null; then this must of necessity result in an increase in signal outside of its region. These are all commonplace observations discussed here that are observable for either Ham or SWL operations. There is NO differential offered in these observations that separate SWL from Ham activities. Certainly there is. A narrow null takes little power from the pattern: you get little gain by putting that in a broad lobe. For example, an elementary dipole has, theoretically, infinitely deep nulls yet it only has about 2 dBi gain. Now consider a phased array: small phasing errors have little effect on the gain, but they can have a large effect on the null depth. When transmitting, you're generally interested in putting the power in the right place, but when receiving you're often more interested in avoiding picking up power from the wrong place. These considerations are only weakly related. Such examples of small loops used for MF are proof positive how poor an antenna can be, and the RF gain knob resurrecting its pitiful efficiency. But for MWDX reception, efficiency simply isn't an important virtue. I believe I have said that at least 3 to 5 times already. Gain is cheap. What matters is the steerable nulls. An efficient *steerable* MW antenna is enormous and expensive. Who needs an efficient MW antenna? People who transmit, of course! Speaking of strawmen, have you ever actually tried DXing with a crystal radio? Sure, what is so remarkable about that? Beyond this simple design, ever hear of a super-Regen receiver? You don't need to spend half a kilo-buck to get the same sensitivity and filtering is dirt cheap. Sure. Used them. Selectivity is *lousy*. For SW, I've gotten better results with a plain regen. Still, my Drake R-8 is better for DX, my Sony ICF-SW100 travels easy, and my Stromberg-Carlson 58-T sounds wonderful, so I haven't played with a regen in quite a while. How about Q-multipliers? All such topics barely spread the wallet as much as the illusion of more buttons make a better rig. I have a Heathkit Q-multiplier I built in 1965. It's pretty good at nulling out unwanted carriers, but in peak mode the shape factor of a single resonance is pretty poor. At the moment I don't have a working receiver it's really suited to, but I have a Halli S-40 one of my in-laws gave me, and one of these days I'll find the time to repair it (it's in really poor shape). The S-40 could probably use a Q-multiplier once I've got it in working order. I love designing and building antennas: applied physics is fun. But it's good engineering to go with the strengths of your technology. For my inverted-L's, I spend a little efficiency (4 dB or so) to get octaves of effective bandwidth, something that is perhaps of little use to hams, but is very useful to an SWL in conjunction with the frequency agility of a modern receiver. 4 dB of efficiency loss is of negligible consequence at HF and below if your receiver has a decent noise figure. As I pointed out to Yahoo, if you choose to cripple yourself, then slide on over to the shoulder and enjoy kicking up dust and rocks as you travel down the road. a 4dB loss for an inverted L (hardly a SW invention) is far too simple to remedy to make its suffering a boast of martyrdom. It is a strange argument to offer that you can't afford a $20 solution for your $500 set and $2 worth of wire. How would you undo that 4 dB loss without loss of bandwidth? I'm hardly boasting of martyrdom anyway: a broadband inverted L is a fine general purpose receiving antenna. I've never seen mention of this efficiency/bandwidth tradeoff in the ham literature, You haven't looked. Either contrived, wholly fictional, or accurately represented, it is part of the stock in trade for selling antennas. In this group, I would wager its discussion consumes more bandwidth than bragging about how many QSL cards have been pasted to the wall. Examples? but it's not hard to find in the professional literature. For details of a specific calculation, see: http://anarc.org/naswa/badx/antennas/SWL_longwire.html -jpd It would do you well to note that this "professional" whom you rely upon, John Kraus, is one of the most notable Ham Radio Operators frequently acknowledged and referred to here. He knew a great deal about the full range of antenna designs and applications, not just ham radio. And he sure knew his physics. Do you or others have any actual differentiable discussion, or is this simply an outlet for appoligia for why it isn't worth the strain to lift a soldering iron when you can bench press a credit card? When a soldering iron is the best tool to get the job done, I lift a soldering iron. The Stromberg-Carlson was a "bare chassis" restoration: most of the resistors were 50% off value, the paper capacitors were leaking, the electrolytics were dry, and one of the RF coils was open (disassembling and reassembling the coil turret was a real pain). Still, it was worth the work to get that wonderful sound. The NASA certified techs I work with professionally tell me I'm pretty good with a soldering iron, considering I'm a physicist. From them, that's high praise :-) -jpd |
On Tue, 29 Jun 2004 22:41:44 -0600, John Doty
wrote: Consider a lamp dimmer that generates 10 mW of RFI, which rides out in common mode on the mains, finds its way to the power cord of your transceiver, rides out on the feedline to the antenna, and then couples back through differential mode to your receiver input. That's not a very efficient coupling path, so suppose it has a loss of 60 dB. You'll still get 10 nW to the receiver. This is a lot: even if it's spread over 30 MHz, it's still 10 uV in a 6 kHz channel. That's S6 on my Drake R-8, a very serious quantity of noise. 10 uV into 50 ohms is 2 pW, not 10 nW (E^2/R). 2 pW = -117 dBW = -87 dBm. Multiplying by 30000/6 = 5000 buckets makes 10 nW or -50 dBm. Cancel the assumed 60 dB loss and I get +10 dBm, or 10 mW. The numbers add up fine. As I said, one of the two of us was being pencil-whipped. This does nothing to change the fact that the original term has no basis in fact. It could as easily be laid to the effects of a nuclear EMP 2000 miles away. There will always be something to blame, and that is NOT a solution nor is it differentiable between Ham and SWL antennas. However, if I return to the original "problem" of noise derived from household sources; then that is also something I have closely measured. Across time, frequency, antennas, and known noise sources I have found it as low as S1 for my longwire (an antenna supposedly unused by Hams) to as high as S7 (for that same longwire). My loops, dipoles and verticals hardly fell outside of this range to present any gilt-edge design. Just because you couldn't doesn't mean others can't. Can't WHAT? The numbers I offer are shown of direct experience correlatable to real world conditions and conform to 3 Sigma of SWL conditions. Being correlatable they were also resolved and reduced to that same unpowered baseline without forcing me off the grid into darkness. My station sits with a noise flicker based upon atmospherics and radiation borne products, not the usual household pollution that I both describe above and eliminated through techniques described as commonplaces in this group. There are no magic antennas and no magic rituals equal to these commonplace practices that are offered here. Look at the rest of the articles on the BADX site. Taking steps to minimize common mode coupling has worked very well for me, and many people tell me it works for them too. This material is NOT novel by any stretch of the imagination. However, it is hardly fully encompassing and falls short of the entire treatment. The notion that a spike in the ground solves common mode reveals a very limited experience in the matter, and simply devolves to the misty eyed sentimentality of "it works for me, so there is no better way for you." Testimonial is a poor substitute for how and why - especially when the suggested solution inevitably fails for someone. The common response in that situation is to sneer them away as somehow deserving their predicament - again, with no one knowing the basis of the problem, they can hardly help but repeat the same nostrum now shown to fail somewhere (an anathema in religion). You might also find the articles at http://www.qsl.net/wa1ion/ These suggestions grow more bizarre by the posting where the correspondent offers that SWLers ignore Amateur advice as poor quality (a remark from a noted Yahoo), and then offer proof of their own beguiling theories through quotes from - Amateur references. interesting, especially the one entitled "Another Look at Noise Reducing Antennas". Mark's antenna designs are generally useless for transmitting, but they make superb MWDX receiving antennas. I cannot see how injecting the notion of uselessness is a boon for an argument upon a physicist who can understand the notion of symmetry or what is called in this field of study, reciprocity. If it is useless as a transmit antenna, is it useless as a receive antenna? Of course not, as such the injection of this comment serves no purpose other than rhetorical noise. The problem with such a degraded S/N in the correspondence of ideas is that the larger body of uninitiated SWLers come to the conclusion that this "uselessness" is a positive boon to be sought in every antenna design. Our eminent Yahoo wears this badge of anti-intellectualism as a patronizing populist. This discussion also reveals a poverty of alternative designs that have equal or superior merits, even if devoid of transmitting application. Those designs are widely discussed here and their merits are weighed not in prejudicial terms but rather in technical comparisons and their correlation to application. That is to say, anyone can make an informed decision on the basis of these evaluations offered here where we typical discard "testimonials" to the rubbish heap. A narrow null takes little power from the pattern: you get little gain by putting that in a broad lobe. For example, an elementary dipole has, theoretically, infinitely deep nulls yet it only has about 2 dBi gain. Now consider a phased array: small phasing errors have little effect on the gain, but they can have a large effect on the null depth. Again, this exposes a lack of experience in the matter. Those nulls are balanced against the theoretical radiator called an isotropic source. This is the i of the 2dBi (and in fact is actual;y higher than that value). Worse yet, this lack of experience further pollutes the uninitiated SWLer's notion of this balance of ledger because no one on this earth is ever going to experience that 2dB gain (nor the supposed sharp nulls) - and simply due to earth being nearby (an irreconcilable fact of life that extends out beyond 6 Sigma for the population of listeners). A simple dipole one quarterwave above earth exhibits an additional 3dB gain above and beyond your cited number. This goes to show how your casually abandoned 4dB for an inverted L is so simply recovered - through real comparisons rather than xeroxed theories. The level of discussion is so unbalanced with myth, superstition and hearsay that the casual SWLer seeking advice faces the problem of sorting out the **** from the shinola. If I were to hike the dipole a little more, it shows 8dB gain after allowing a real world loss of 1dB. To tell that same casual SWLer 4dB is no great loss gives a spread of 10dB. The consequence of this challenging this poor coverage of intellectual offering is that the casual SWLer having the facts known, can in fact choose to build a less optimal antenna, one that suits his real world limitations, and enjoy a design that does not simply discard signal with abandon. Alternatively, a simpler receiver can perform with an excellent antenna as well as a box full of expensive knobs can with an air cooled resistor. When transmitting, you're generally interested in putting the power in the right place, but when receiving you're often more interested in avoiding picking up power from the wrong place. These considerations are only weakly related. This has been spoken too, the limitation is found in the signal and noise being aligned along the same meridian. If there is any weak relation it is found in the chance of distribution. The laws of reciprocity are not violated by chance, and both Ham operator and SWLer suffer the same odds. There is NOTHING separable here. Who needs an efficient MW antenna? People who transmit, of course! And SWLers are not transmitting are they? Really, these specious arguments do not advance any notion of this being separate issues. There is nothing in the circularity of logic that demands poorer transmit antenna designs are better receive antenna designs. Nearly every beneficial description from your sources cited above lie outside of the antenna and reside in the coupling or in the receiver. Such commonplaces are not novel; they are not unique and special knowledge; and they are certainly not universally applicable. How would you undo that 4 dB loss without loss of bandwidth? That has been responded to above. Loss of bandwidth is a chimera suited for argument rather than operation. To say it is frequency agile is the crowning claim for someone who is fain to turn a switch and set a capacitor in 5 seconds. This isn't rocket surgery, children learn such techniques within minutes of explanation and faithfully demonstrate far less loss consistently for ever after. Further, the usage of a tuner solves many other ills related to noise and front end overload. The argument of the 9:1 transformer to ease operation comes at the expense of simple cheap solutions - to no great benefit, and further, to 4 dB additional loss as you describe. What boon is to be found in that combination? I find it laughable that one web site offered claims that a resonant system is bad for your reception. What a crock! This has all the logic of buying square wheels to increase your gas mileage. I'm hardly boasting of martyrdom anyway: a broadband inverted L is a fine general purpose receiving antenna. And what distinguishes it as a poor transmitting antenna? The inclusion of the engineering decoration of the 9:1 transformer? This logic is destroyed by a conventional tube transmitter (the original application suited to this design). Once again, every issue in relation to even this point is discussed as a commonplace in this group with simple and cheap solutions that perform without the concurrent 4dB loss. Such a cavalier attitude of discarding signal is evidence of purchasing power, not technical competence. I've never seen mention of this efficiency/bandwidth tradeoff in the ham literature, You haven't looked. Either contrived, wholly fictional, or accurately represented, it is part of the stock in trade for selling antennas. In this group, I would wager its discussion consumes more bandwidth than bragging about how many QSL cards have been pasted to the wall. Examples? As I offered, you need to look rather than claim. They are so common that if they escape your attention, no work on my part is going to satisfy you. So, the question remains: Do you or others have any actual differentiable discussion, or is this simply an outlet for appoligia for why it isn't worth the strain to lift a soldering iron when you can bench press a credit card? 73's Richard Clark, KB7QHC |
"Mark1" wrote in message
... pse remove the nl newsgroup from this discussion. Loop niet zo te zeuren Mark1, deze draad is gestart door een Nederlander (Kees) en ge-crosspost naar twee engelse groepen. Dus dat deze heren hier steeds weer terugkomen is gewoon deel van de originele discussie. Meindert |
Meindert Sprang bracht volgend idée uit :
"Mark1" wrote in message ... pse remove the nl newsgroup from this discussion. Loop niet zo te zeuren Mark1, deze draad is gestart door een Nederlander (Kees) en ge-crosspost naar twee engelse groepen. Dus dat deze heren hier steeds weer terugkomen is gewoon deel van de originele discussie. Meindert Wat een onzin Meindert, ik vraag gewoon of ze deze nieuwsgroep eruit willen halen, het is en blijft een Nederlandse nieuwsgroep. De 'draad' is gestart door Kees met reclame maken voor zijn website met daarop zijn eigen gebouwde antenne, daar staat netjes bij dat hij wel vragen wilt beantwoorden, nou prima maar dan wel op zijn e-mail adres graag. |
John Doty wrote:
Consider a lamp dimmer that generates 10 mW of RFI, which rides out in common mode on the mains, finds its way to the power cord of your transceiver, rides out on the feedline to the antenna, and then couples back through differential mode to your receiver input. That's not a very efficient coupling path, so suppose it has a loss of 60 dB. You'll still get 10 nW to the receiver. This is a lot: even if it's spread over 30 MHz, it's still 10 uV in a 6 kHz channel. That's S6 on my Drake R-8, a very serious quantity of noise. What is the actual coupling process between common and differential mode at the far (antenna) end of the coax? -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
RC,
The initial poster cross-posted the original Post to three NewsGroups. 1. rec.radio.shortwave 2. rec.radio.amateur.antenna 3. nl.radio.amateur Then to just two: 1. rec.radio.shortwave 2. rec.radio.amateur.antenna This reply is ONLY to: Rec.Radio.Shortwave {RRS} I can see by your "WPE" Call-Sign that at one time you were a SWL'er. But you have gone way beyond that now and are a Licensed Amateur Radio Operator. I concede that you have far superior technical expertise then myself in the area of antennas and more. I simply remain a SWL'er I will repeat part of my prior post: "Spoken (written) like a True Amateur, and precisely why most SWLs ignore what is written in reply to SWL 'type' Antennas questions by HAMs." As an Amateur 'you' talk down to me as a SWL and use your knowledge and expertise to Attack and attempt to humble me as a SWL. Everything that you have said may be true. But IMHO it is way beyond what a SWL needs to know to simply build a SWL Antenna to meet their listening needs with a 'portable' SW Radio or may be a table top General Coverage Receiver. An Antenna that will fit the 'limits' of their Available Space and other building and property restrictions. A SWL Antenna that will make their SWL'ing more interesting and enjoyable. RC - What you have written and the tone that you take would simply turn most new SWL'ers off. iane ~ RHF .. .. = = = Richard Clark wrote in message = = = . .. On 29 Jun 2004 11:30:01 -0700, (RHF) wrote: RC (KB7QHC), Spoken (written) like a True Amateur, and precicly why most SWLs ignore what is written in reply to SWL 'type' Antennas questions by HAMs. Strange logic to offer that a listener comes here to post a query they will ignore in anticipation. Rather self serving argument isn't it? Most SWLs work to get the best signal (cleanest signal and lowest noise) they can to be able to listen to what they what to hear. There is nothing in this statement that distinguishes amateur from listener. Further, it contains absolutely no technical material to support any sense of this exclusivity of concern. To respond in kind, you don't even rise to amateur status. But there is a real difference between the radio receiving focus of a SWL'er and a HAM. I simply offered my opinion and nothing more; but feel free to use all the Technical Material you feel necessary to support your position. I have never claimed 'amateur' "Status"; and I did not think that on Rec.Radio.Shortwave a License was required. .. .. The HAM would hardly ever consider a 'random' wire Antenna; Now this is a statement that is clearly in error. The archives will attest to this. This may be a matter of perception and degree. .. .. but to the SWL'er the "Random" Wire Antenna 'concept' is a natural to fill their available space. Power handling, gain and antenna design characteristics are the focus of the HAM. As they are no more or less for a listener. If you find some other motivation, it is strictly your own prejudice. ? motivation ? prejudice ? .. .. As far as the AM/MW Loop Antenna's are concerned. For the AM/MW DX'er these Antenna's perform the best for their size and the available space that the average Broadcast Listener (BCL) has for these Medium Wave Band. The SWL'er wants to hear any Radio Station out there from any direction. Perhaps you should attend this board more often to learn the fundamentals. There is no impediment to hearing any Radio Station out there from any direction with simple verticals. SW sets come with them you know. Yes many 'portable' SW Radio have small Whip Antennas built-in to the radios. But to the SWL'er attempting to use an External Antenna to Hear-More. A Vertical Antenna that is subject to more RFI/EMF would not be my first suggestion. A Horizontal Random Wire or Inverted "L" Antenna using Low Noise design concepts would be what I would recommend. Here are Three Links to give you an idea of what I am talking about: http://www.anarc.org/naswa/badx/ante...e_antenna.html http://www.anarc.org/naswa/badx/ante..._longwire.html http://www.anarc.org/naswa/badx/antennas/grounding.html .. .. The 'focus' of the SWL'er is simpy different then the Amateur; and the majority of SWL'ers are Program Listeners who seldom listen to the HAM Bands. So why are you posting to an amateur group? Why an antenna group? You would be better served through your self-imposed limitations by staying out of the fast lane. The initial poster cross-posted the original Post to three NewsGroups. 1. rec.radio.shortwave 2. rec.radio.amateur.antenna 3. nl.radio.amateur Then to just two: 1. rec.radio.shortwave 2. rec.radio.amateur.antenna This reply is ONLY to: Rec.Radio.Shortwave {RRS} I have never claimed 'amateur' "Status"; and I did not think that on Rec.Radio.Shortwave a License was required. .. .. 73's Richard Clark, KB7QHC, WPE0EPH p.s. if the WPE0EPH is unknown to you, it denotes my having been a Shortwave listener for 40 years and registered with the Popular Electronics DX club (as well as a sack full of others from around the world). "Were You a WPE ?" http://www.qsl.net/wb1gfh/swl.html http://www.w8pgw.org/node/view/386 http://www181.pair.com/otsw/WPE.html WDX Monitor Services P.O. Box 9 Collingswood, NJ 08108 http://kc5jk.tripod.com/sitebuilderc...files/wdx.html Short Wave Listening group issues call signs and awards http://ej.typepad.com/k8zrh/2003/10/...wave_list.html Short Wave Amateur Radio Listening (SWARL) COMMENTARY: SWL CALL SIGNS / DYING HOBBY http://www.worldofradio.com/dxld3169.txt DX LISTENING DIGEST 3-169, September 21, 2003 Edited by Glenn Hauser .. |
starman wrote:
John Doty wrote: Consider a lamp dimmer that generates 10 mW of RFI, which rides out in common mode on the mains, finds its way to the power cord of your transceiver, rides out on the feedline to the antenna, and then couples back through differential mode to your receiver input. That's not a very efficient coupling path, so suppose it has a loss of 60 dB. You'll still get 10 nW to the receiver. This is a lot: even if it's spread over 30 MHz, it's still 10 uV in a 6 kHz channel. That's S6 on my Drake R-8, a very serious quantity of noise. What is the actual coupling process between common and differential mode at the far (antenna) end of the coax? Consider first an open circuited coax cable hanging in mid air. In coax, the common mode is carried only on the shield, while the differential mode is carried by opposing currents on the shield and center conductor. Since the shield is open circuited, the sum of the common mode and differential mode currents on the shield must be zero at the end. But the differential mode current must also be zero, since the center conductor is open circuited. We therefore conclude that the common mode current must also be zero at this point: the shield current cannot be balanced by driving a differential mode current. Now attach a wire to the center conductor. Now a current can flow out from the center conductor to the wire, so the common mode shield current can be balanced by a differential mode shield current: the common mode energy thus drives a differential mode current. The misnamed "magnetic longwire balun" doesn't help here, since it can't suppress this coupling without also suppressing the coupling of the antenna to the differential mode: it has no way of distinguishing the current from energy coming down the wire from the current due to energy coming up the coax. If you connect the shield to an infinite, perfectly conducting ground plane, all of the common mode current flows that way. This is why a ground stake at the feedpoint helps (although in real life it's not perfect). With a balanced antenna things are generally better, but more complicated: without a balun, the common mode on the coax will excite a combination of common and differential modes on the antenna. A balun can help, but practical baluns are not ideal devices. Furthermore, the common mode on the coax can couple electrostatically or magnetically to nearby conductors like the antenna. Careful orientation of the line with respect to a balanced antenna can minimize this, but it's difficult to avoid some coupling in practice. Given that the methods for decoupling the common mode from the differential mode at the antenna are imperfect, it's often a good idea to try to keep the common mode energy away from the antenna in the first place. -jpd |
Nou weet ik wat ze in plaats van dat Morse hadden moeten doen: Engels.
73 Hans, PA0H "Mark1" wrote in message ... Meindert Sprang bracht volgend idée uit : "Mark1" wrote in message ... pse remove the nl newsgroup from this discussion. Loop niet zo te zeuren Mark1, deze draad is gestart door een Nederlander (Kees) en ge-crosspost naar twee engelse groepen. Dus dat deze heren hier steeds weer terugkomen is gewoon deel van de originele discussie. Meindert Wat een onzin Meindert, ik vraag gewoon of ze deze nieuwsgroep eruit willen halen, het is en blijft een Nederlandse nieuwsgroep. De 'draad' is gestart door Kees met reclame maken voor zijn website met daarop zijn eigen gebouwde antenne, daar staat netjes bij dat hij wel vragen wilt beantwoorden, nou prima maar dan wel op zijn e-mail adres graag. |
Als je mijn vertaling van het stukje babbelfish hebt gelezen weet je
dat dat dus niet het probkeem is, maar wel dat dit een Nederlandse Nieuwsgroep is en dus de voertaal Nederlands is. J.W.Siebelink plaatste dit op zijn scherm : Nou weet ik wat ze in plaats van dat Morse hadden moeten doen: Engels. 73 Hans, PA0H "Mark1" wrote in message ... Meindert Sprang bracht volgend idée uit : "Mark1" wrote in message ... pse remove the nl newsgroup from this discussion. Loop niet zo te zeuren Mark1, deze draad is gestart door een Nederlander (Kees) en ge-crosspost naar twee engelse groepen. Dus dat deze heren hier steeds weer terugkomen is gewoon deel van de originele discussie. Meindert Wat een onzin Meindert, ik vraag gewoon of ze deze nieuwsgroep eruit willen halen, het is en blijft een Nederlandse nieuwsgroep. De 'draad' is gestart door Kees met reclame maken voor zijn website met daarop zijn eigen gebouwde antenne, daar staat netjes bij dat hij wel vragen wilt beantwoorden, nou prima maar dan wel op zijn e-mail adres graag. |
Meindert Sprang schreef :
"Mark1" wrote in message ... Als je mijn vertaling van het stukje babbelfish hebt gelezen weet je dat dat dus niet het probkeem is, maar wel dat dit een Nederlandse Nieuwsgroep is en dus de voertaal Nederlands is. Mark1, je bent nu zelf net zo erg, want je haalt niet even de engelse groepen uit de lijst, dus jij zit nu Nederlands te lullen in een engelstalige nieuwsgroep. De pot verwijt de ketel... Meindert Dit is niet de pot verwijt de ketel, enkel het laten zien aan de engelstalige nieuwsgroeppen hoe hindelijk het is als er iemand in een andere taal schrijft, als ze het dan proberen te vertalen in babbelfish of een andere vertaalprogramma zullen ze zien dat er geen barst van klopt. Vandaar dat ik nu dus weer die engelstalige groepen die jij eruit hebt gehaald erbij heb gezet :-P |
= = = Telamon wrote in message
= = = ... In article , (RHF) wrote: RC (KB7QHC), Spoken (written) like a True Amateur, and precicly why most SWLs ignore what is written in reply to SWL 'type' Antennas questions by HAMs. Richard Clark is a goof that hangs out in rec.radio.amateur.antenna which is a good reason to ignore him. News group header sniped to RRS. TELAMON, "RC" writes very well, and has a great deal of technical expertise and experience. But the 'tone' of his writing when dealing with lesser beings (SWLs) is what I find to be a turn-off. ~ RHF .. |
In article ,
(RHF) wrote: = = = Telamon wrote in message = = = ... In article , (RHF) wrote: RC (KB7QHC), Spoken (written) like a True Amateur, and precicly why most SWLs ignore what is written in reply to SWL 'type' Antennas questions by HAMs. Richard Clark is a goof that hangs out in rec.radio.amateur.antenna which is a good reason to ignore him. News group header sniped to RRS. TELAMON, "RC" writes very well, and has a great deal of technical expertise and experience. But the 'tone' of his writing when dealing with lesser beings (SWLs) is what I find to be a turn-off. Sure, he writes a great line of BS, but he's wrong about 50% of the time. He's full of it and full of himself. -- Telamon Ventura, California |
RC,
.. You write well and are an easy read. But a casual Shortwave Radio Program Listener would be put-off by the tone and technical details of your replys. .. What more can I say except that I am a SWL {No License Required} ~ RHF .. .. = = = Richard Clark wrote in message = = = . .. On Tue, 29 Jun 2004 22:41:44 -0600, John Doty wrote: Consider a lamp dimmer that generates 10 mW of RFI, which rides out in common mode on the mains, finds its way to the power cord of your transceiver, rides out on the feedline to the antenna, and then couples back through differential mode to your receiver input. That's not a very efficient coupling path, so suppose it has a loss of 60 dB. You'll still get 10 nW to the receiver. This is a lot: even if it's spread over 30 MHz, it's still 10 uV in a 6 kHz channel. That's S6 on my Drake R-8, a very serious quantity of noise. 10 uV into 50 ohms is 2 pW, not 10 nW (E^2/R). 2 pW = -117 dBW = -87 dBm. Multiplying by 30000/6 = 5000 buckets makes 10 nW or -50 dBm. Cancel the assumed 60 dB loss and I get +10 dBm, or 10 mW. The numbers add up fine. As I said, one of the two of us was being pencil-whipped. This does nothing to change the fact that the original term has no basis in fact. It could as easily be laid to the effects of a nuclear EMP 2000 miles away. There will always be something to blame, and that is NOT a solution nor is it differentiable between Ham and SWL antennas. However, if I return to the original "problem" of noise derived from household sources; then that is also something I have closely measured. Across time, frequency, antennas, and known noise sources I have found it as low as S1 for my longwire (an antenna supposedly unused by Hams) RC - A "HAM" would in-fact use a Longwire Antenna cut for a specific band. However, a SWL'er would simply use a "Random Wire" Antenna to use on all bands. .. .. to as high as S7 (for that same longwire). My loops, dipoles and verticals hardly fell outside of this range to present any gilt-edge design. Just because you couldn't doesn't mean others can't. Can't WHAT? The numbers I offer are shown of direct experience correlatable to real world conditions and conform to 3 Sigma of SWL conditions. "conform to 3 Sigma of SWL conditions" RC - How Would You Know ? .. .. Being correlatable they were also resolved and reduced to that same unpowered baseline without forcing me off the grid into darkness. My station sits with a noise flicker based upon atmospherics and radiation borne products, not the usual household pollution that I both describe above and eliminated through techniques described as commonplaces in this group. RC - Yes as a HAM you may indeed have your station near a noise flicker based upon atmospherics and radiation borne products. But again the average SWL'er would not go to all that effort. To the SWL'er an 'outside' External Antenna that is built with Low Noise design concepts puts them into the area of Strong Signals and "Good Listening". ? Why Do More ? .. .. There are no magic antennas and no magic rituals equal to these commonplace practices that are offered here. Look at the rest of the articles on the BADX site. Taking steps to minimize common mode coupling has worked very well for me, and many people tell me it works for them too. This material is NOT novel by any stretch of the imagination. However, it is hardly fully encompassing and falls short of the entire treatment. The average SWL'er is not a HAM and does not require the 'entire treatment' to get a low noise strong signal and "Good Listening". RC - As a Licensed Amateur Operator you may be keenly interested in the Whys and Wherefores of All-Things-Technical. But again the average SWL'er would like to see a picture/diagram and read a paragraph of text that they could make the decision to build or buy the radio or antenna. .. .. The notion that a spike in the ground solves common mode reveals a very limited experience in the matter, and simply devolves to the misty eyed sentimentality of "it works for me, so there is no better way for you." Testimonial is a poor substitute for how and why - especially when the suggested solution inevitably fails for someone. "conform to 3 Sigma of SWL conditions" Yes even 3 Sigma (99.73%) leaves 27 failures in 10,000. But you forget the 9,973 success out of 10,000. Or 997 success out of 1000. or 99 success out of 100. RC - Alas there are no perfect solutions to all problems and in-fact One-Size does not Fit-All. .. .. The common response in that situation is to sneer them away as somehow deserving their predicament - again, with no one knowing the basis of the problem, they can hardly help but repeat the same nostrum now shown to fail somewhere (an anathema in religion). You might also find the articles at http://www.qsl.net/wa1ion/ These suggestions grow more bizarre by the posting where the correspondent offers that SWLers ignore Amateur advice as poor quality (a remark from a noted Yahoo), and then offer proof of their own beguiling theories through quotes from - Amateur references. RC - If the Advice is over-the-head of the SWL'ers or not-applicable to the SWL'ers needs; then indeed it generally gets ignored. And Thank for the 'noted' Yahoo comment RC - Some would say a Yahooligan! :o) .. .. interesting, especially the one entitled "Another Look at Noise Reducing Antennas". Mark's antenna designs are generally useless for transmitting, but they make superb MWDX receiving antennas. I cannot see how injecting the notion of uselessness is a boon for an argument upon a physicist who can understand the notion of symmetry or what is called in this field of study, reciprocity. If it is useless as a transmit antenna, is it useless as a receive antenna? Of course not, as such the injection of this comment serves no purpose other than rhetorical noise. "this comment serves no purpose other than rhetorical noise." RC - That it does :o) .. .. The problem with such a degraded S/N in the correspondence of ideas is that the larger body of uninitiated SWLers come to the conclusion that this "uselessness" is a positive boon to be sought in every antenna design. RC - To the 'lareger body of uininitiated SWLers' What works... WORKS ! Our eminent Yahoo wears this badge of anti-intellectualism as a patronizing populist. RC - So you have promoted me from 'noted' to 'eminent' A Yahooligan! I Am :o) "anti-intellectualism as a patronizing populist" RC - When speaking to the average SWL'er it is good to keep things understandable; and in a form that can be put to use without adding any unnecessary information that is not needed to accomplish the task. {Its About Communications} .. .. This discussion also reveals a poverty of alternative designs that have equal or superior merits, even if devoid of transmitting application. Those designs are widely discussed here and their merits are weighed not in prejudicial terms but rather in technical comparisons and their correlation to application. That is to say, anyone can make an informed decision on the basis of these evaluations offered here where we typical discard "testimonials" to the rubbish heap. RC - All that you say may fair well for technically orientated Licensed Amateur Operators who may have several antennas. But the majority of SWL'ers will use a single 'outside' antenna for their Shortwave Listening needs. If one of the better choices for a SWL'er is a Random Wire or Inverted "L" Antenna that uses low noise design concepts; and can be built within their available space. So... Why not start their first. .. .. A narrow null takes little power from the pattern: you get little gain by putting that in a broad lobe. For example, an elementary dipole has, theoretically, infinitely deep nulls yet it only has about 2 dBi gain. Now consider a phased array: small phasing errors have little effect on the gain, but they can have a large effect on the null depth. Again, this exposes a lack of experience in the matter. Those nulls are balanced against the theoretical radiator called an isotropic source. This is the i of the 2dBi (and in fact is actual;y higher than that value). Worse yet, this lack of experience further pollutes the uninitiated SWLer's notion of this balance of ledger because no one on this earth is ever going to experience that 2dB gain (nor the supposed sharp nulls) - and simply due to earth being nearby (an irreconcilable fact of life that extends out beyond 6 Sigma for the population of listeners). A simple dipole one quarterwave above earth exhibits an additional 3dB gain above and beyond your cited number. RC - The classic 'bad answer' for a HAM to a SWL'er is the simple Dipole. Most SWL'ers do not have the available space for a not-s-simple Dipole Antenna that will 'cover all' the Shortwave Bands and the ability to put the Dipole up high enough for proper operation. .. .. This goes to show how your casually abandoned 4dB for an inverted L is so simply recovered - through real comparisons rather than xeroxed theories. The level of discussion is so unbalanced with myth, superstition and hearsay that the casual SWLer seeking advice faces the problem of sorting out the **** from the shinola. If I were to hike the dipole a little more, it shows 8dB gain after allowing a real world loss of 1dB. To tell that same casual SWLer 4dB is no great loss gives a spread of 10dB. The consequence of this challenging this poor coverage of intellectual offering is that the casual SWLer having the facts known, can in fact choose to build a less optimal antenna, one that suits his real world limitations, and enjoy a design that does not simply discard signal with abandon. Alternatively, a simpler receiver can perform with an excellent antenna as well as a box full of expensive knobs can with an air cooled resistor. When transmitting, you're generally interested in putting the power in the right place, but when receiving you're often more interested in avoiding picking up power from the wrong place. These considerations are only weakly related. This has been spoken too, the limitation is found in the signal and noise being aligned along the same meridian. If there is any weak relation it is found in the chance of distribution. The laws of reciprocity are not violated by chance, and both Ham operator and SWLer suffer the same odds. There is NOTHING separable here. Who needs an efficient MW antenna? People who transmit, of course! And SWLers are not transmitting are they? Really, these specious arguments do not advance any notion of this being separate issues. There is nothing in the circularity of logic that demands poorer transmit antenna designs are better receive antenna designs. Nearly every beneficial description from your sources cited above lie outside of the antenna and reside in the coupling or in the receiver. Such commonplaces are not novel; they are not unique and special knowledge; and they are certainly not universally applicable. How would you undo that 4 dB loss without loss of bandwidth? That has been responded to above. Loss of bandwidth is a chimera suited for argument rather than operation. To say it is frequency agile is the crowning claim for someone who is fain to turn a switch and set a capacitor in 5 seconds. RC - Some SWL'ers simply want an Antenna and Radio with NO 'other' complications; for them its about Listening Enjoyment. Others SWL'ers may want more 'gadgets' to Help them to improve their ability to hear more signals. .. .. This isn't rocket surgery, children learn such techniques within minutes of explanation and faithfully demonstrate far less loss consistently for ever after. RC - Its a matter of personal choice and many casual SWL'ers choose to keep it simple. A relaxing hobby that provides interesting and enjoyable listening. .. .. Further, the usage of a tuner solves many other ills related to noise and front end overload. RC - That can be true; but to many SWL'ers it is simply another gadget that starts to make things complicated. The argument of the 9:1 transformer to ease operation comes at the expense of simple cheap solutions RC - What could be more simpler and 'cheap' then a passive static devise like a Matching Transformer ? To paraphase what they say on the TV 'Connect It and Forget It'. .. .. - to no great benefit, and further, to 4 dB additional loss as you describe. What boon is to be found in that combination? RC - For many SWL'ers it gets the job done. What works... Works! .. .. I find it laughable that one web site offered claims that a resonant system is bad for your reception. RC - If the system is resonant on one band 'only' and the SWL'er wants an Antenna that works well on All the Bands. Then just may be resonant is not the best answer to the needs of the SWL'er. .. .. What a crock! This has all the logic of buying square wheels to increase your gas mileage. I'm hardly boasting of martyrdom anyway: a broadband inverted L is a fine general purpose receiving antenna. And what distinguishes it as a poor transmitting antenna? The inclusion of the engineering decoration of the 9:1 transformer? This logic is destroyed by a conventional tube transmitter (the original application suited to this design). RC - But the modern day SWL'er is not using a 'tube' anything. The SWLer using Inverted "L" Antenna; using a Wire Antenna Element; coupled by a Matching Transformer; with a Grounding Point collocated at the junction of the Antenna Element and the Coax Cable; plus a Coax Cable Feed-in-Line to the Radio/Receiver. Where the HAM may have used an Inverted "L" Antenna with the Vertical (Leg) and the Horizontal (Arm) of Equal Lengths and in 1/8WL, 1/4WL or 1/2WL sizing. The SWL'er would most likely use an Inverted "L" Antenna with the a 'shorter' Vertical (Leg) and a 'longer' Horizontal (Arm) of 2X-3X the Vertical (Leg). - An Antenna to fit and fill their available space. - An Antenna that lends itself naturally to Low Noise Antenna design concepts. .. .. Once again, every issue in relation to even this point is discussed as a commonplace in this group with simple and cheap solutions that perform without the concurrent 4dB loss. Such a cavalier attitude of discarding signal RC - For the SWL Signal is not discarded to the extent that RFI/EMF background noise is reduced by a greater amount; with an overall improvement in the Signal-to-Noise Ratio. The Radio/Receivers AGC Circuit then compensates for the lower signal level. The result for the SWL'er is an improved and enjoyable Listening Experience. Remember most SWLs are simply Broadcast Program Listeners seeking news, information and entertainment from other countries via the Shortwave Bands. The vast majority approach being a SWL with the basic experience of the average Car AM/FM Radio listener. Their beginnings are not your beginnings and their experiences are not your experiences. .. .. is evidence of purchasing power, not technical competence. RC - yes, Yes. YES ! To the majority of SWL'ers it is ABOUT "Purchasing Power" and to most SWL'ers your level of 'technical competence' simply does not apply to their needs. ? How many SWL'ers actually read their radio's Owner's Manual from Front-to-Back ? .. .. I've never seen mention of this efficiency/bandwidth tradeoff in the ham literature, You haven't looked. Either contrived, wholly fictional, or accurately represented, it is part of the stock in trade for selling antennas. In this group, I would wager its discussion consumes more bandwidth than bragging about how many QSL cards have been pasted to the wall. Examples? As I offered, you need to look rather than claim. They are so common that if they escape your attention, no work on my part is going to satisfy you. So, the question remains: Do you or others have any actual differentiable discussion, or is this simply an outlet for appoligia for why it isn't worth the strain to lift a soldering iron when you can bench press a credit card? RC - Once Again: yes, Yes. YES ! To the majority of SWL'ers it is ABOUT "Purchasing Power" and to most SWL'ers your level of 'technical competence' simply does not apply to their needs. Maybe 1/4 to 1/3 of the Shortwave Radios bought are purchased as "Gifts' for someone. Some catch the SWL Spirit and many simply use the radios as an AM/FM Radio with out ever getting into Shortwave. For many of those that do catch the SWL Spirit; an 'outside' External Antenna is their next logical "Purchace". Far fewer get 'into' being a SWL and go about informing and educating themselves about the technologies related to SWL. All are SWLs be they casual, average or Expert. .. .. 73's Richard Clark, KB7QHC .. .. What more can I say except that I am a SWL {No License Required} ~ RHF .. .. |
John Doty wrote:
starman wrote: What is the actual coupling process between common and differential mode at the far (antenna) end of the coax? Consider first an open circuited coax cable hanging in mid air. In coax, the common mode is carried only on the shield, while the differential mode is carried by opposing currents on the shield and center conductor. Since the shield is open circuited, the sum of the common mode and differential mode currents on the shield must be zero at the end. But the differential mode current must also be zero, since the center conductor is open circuited. We therefore conclude that the common mode current must also be zero at this point: the shield current cannot be balanced by driving a differential mode current. Now attach a wire to the center conductor. Now a current can flow out from the center conductor to the wire, so the common mode shield current can be balanced by a differential mode shield current: the common mode energy thus drives a differential mode current. The misnamed "magnetic longwire balun" doesn't help here, since it can't suppress this coupling without also suppressing the coupling of the antenna to the differential mode: it has no way of distinguishing the current from energy coming down the wire from the current due to energy coming up the coax. If you connect the shield to an infinite, perfectly conducting ground plane, all of the common mode current flows that way. This is why a ground stake at the feedpoint helps (although in real life it's not perfect). With a balanced antenna things are generally better, but more complicated: without a balun, the common mode on the coax will excite a combination of common and differential modes on the antenna. A balun can help, but practical baluns are not ideal devices. Furthermore, the common mode on the coax can couple electrostatically or magnetically to nearby conductors like the antenna. Careful orientation of the line with respect to a balanced antenna can minimize this, but it's difficult to avoid some coupling in practice. Given that the methods for decoupling the common mode from the differential mode at the antenna are imperfect, it's often a good idea to try to keep the common mode energy away from the antenna in the first place. -jpd I'm trying to visualize the current modes on each conductor, particularly where you say "the shield current cannot be balanced by driving a differential mode current". -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
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