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#41
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= = = 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/ .. |
#42
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#43
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#44
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#46
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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 |
#47
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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 |
#48
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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) |
#49
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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) |
#50
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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 |
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