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SWL for Newbies (was: Balcony Antenna for Shortwave Listening)
On 12 Dec 2010 13:59:06 GMT, Sébastien MEDARD wrote:
The problem seems to be related to wave propagation... I need to test that a little bit more but... It is easier to receive radio broadcast during the night. I need to know what are the differences between night/ day for wave propagation. What should I listen during the night and what I should better listen during daylight... Hi Sébastien, What you are talking about is common to DXing. Get yourself a globe of the world. Light it up with an artificial "sun." The edge of the dark/light should be half way between you and the transmitter you want to hear. So, during the late day, your best signals are probably from Eastern Europe, Turkey, and Asia. During the early-to-late night, your best signals are probably from the Americas. During the late afternoon to early evening you best signals are from the south or the north. I need to know a little bit more about digital transmission modes... To be able to recognize digital patterns (on the waterfall display) to be able apply the good settings for decoding... Easy for CW... Easy for RTTY used by HAM... But what is the pattern for Meteo Faxes for example...? When I used to teach RTTY there were only two tones. If modem technology is any indication, that number has been raised and phase is important. By the way... I searched for good free software to decode meteo faxes... But it seems not easy to find something free and easy to use... Do you know shere I could find something interesting? Nope. My next tries will be on a multiple turns loops. With or without matching loop inside. I will try with simple wire but connection ribbon cables could be a good alternative... (like old hard drive ribbon cable) This will reveal the "Law of Diminishing Returns" (the more you add, the less you get back). I was wondering... It seems loop antennas are a never ending story. As far as I know, it seems there is no book that makes a good overview of the different loop designs, with accessible schematics for preamp or tuning stuff, how to avoid QRMs... There could be a very interesting area both for SWL and HAM... Oh, I am sure there are many such books gathering dust on shelves. Loops have been around for more than a century, and if they were such a good idea, then everyone would be using them. Well, at one time they were a good idea, and EVERYONE used them - when we had transistor pocket radios with analog tuning. The ferrite antenna was the king of antennas for the vast majority of radio owners. Before the transistor radio and ferrites, every table radio had a flat pancake loop antenna in the back of the radio behind all the glowing tubes. Oddly enough, no radios in this age have either of these antennas anymore, and they still seem to pick up stations. So, there you have a century of technical perspective on the topic. Perhaps the "Joe Carr's Loop Antenna Handbook" may be interesting, but it is quite expensive and an Amazon reviewer says it is not so interesting... What about the "Joe Carr's Receiving Antenna Handbook" ? He is a respected author. I always look at the bad Amazon reviews to see if something is terribly wrong with the product or terribly wrong with the customer. Quite often the customer is disappointed because that customer is stupid. If I encounter a smart customer that is disappointed, I can well imagine all the good comments are not very reliable. The thing about all these -um- books is that many of them serve up old wives' tales about low noise and other magical characteristics. Remember the lessons of a century worth of experience with loop antennas within an inch of the guts of any radio. That worked fine for a billion radios and radios were not bought if they were "noisy." The real science of low noise is found in the distance to the source. Quite often it is your neighbor's aquarium heater that is noisy (the most often complained of source of noise reported here). Your loop sits in your shack and that aquarium is 10 Meters away. You switch to your longwire that runs to the fence and the aquarium is 1 meter away. Do I have to work out the math on that? Is the loop quieter because of its magic design - or simply because it is 10 times further away (20dB) from the noise? We get writers here who pound the table because their magic loop in the shack is noisy and their long wire 10M away in the back yard is quiet. They have to be told to turn off the flourescent light in the shack if they want their magic loop to work. (Their magic loop low score on Amazon) = (stupid.) 73's Richard Clark, KB7QHC |
#2
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SWL for Newbies (was: Balcony Antenna for Shortwave Listening)
On Sun, 12 Dec 2010 12:25:59 -0800, Richard Clark wrote:
On 12 Dec 2010 13:59:06 GMT, SĂ©bastien MEDARD wrote: What you are talking about is common to DXing. Get yourself a globe of the world. Light it up with an artificial "sun." The edge of the dark/light should be half way between you and the transmitter you want to hear. So, during the late day, your best signals are probably from Eastern Europe, Turkey, and Asia. During the early-to-late night, your best signals are probably from the Americas. During the late afternoon to early evening you best signals are from the south or the north. I understand better what is the purpose of this kind of map (on SDR- Radio.com software for example). Where you can see an OM, you are pretty sure to see this kind of map. I need to know a little bit more about digital transmission modes... To be able to recognize digital patterns (on the waterfall display) to be able apply the good settings for decoding... Easy for CW... Easy for RTTY used by HAM... But what is the pattern for Meteo Faxes for example...? When I used to teach RTTY there were only two tones. The reason why they call you OM ? ) By the way... I searched for good free software to decode meteo faxes... But it seems not easy to find something free and easy to use... Do you know shere I could find something interesting? Nope. OK. I will try that later... For now I get some problems to use Linrad with the SDR-IQ... Painful to boot on windows every time I want to listen to shortwaves... And using a virtual system is not very efficient on my old computer... My next tries will be on a multiple turns loops. With or without matching loop inside. I will try with simple wire but connection ribbon cables could be a good alternative... (like old hard drive ribbon cable) This will reveal the "Law of Diminishing Returns" (the more you add, the less you get back). Interesting. What would be the best ratio? I was wondering... It seems loop antennas are a never ending story. So, there you have a century of technical perspective on the topic. ) Perhaps the "Joe Carr's Loop Antenna Handbook" may be interesting, but it is quite expensive and an Amazon reviewer says it is not so interesting... What about the "Joe Carr's Receiving Antenna Handbook" ? He is a respected author. I always look at the bad Amazon reviews to see if something is terribly wrong with the product or terribly wrong with the customer. Quite often the customer is disappointed because that customer is stupid. If I encounter a smart customer that is disappointed, I can well imagine all the good comments are not very reliable. I will try to find one when they are cheaper. The thing about all these -um- books is that many of them serve up old wives' tales about low noise and other magical characteristics. Remember the lessons of a century worth of experience with loop antennas within an inch of the guts of any radio. That worked fine for a billion radios and radios were not bought if they were "noisy." OK. But today we probably ask more to radios than yesterday, no? The real science of low noise is found in the distance to the source. Lapalisse would have said exactly the same thing. He would have said that the real science of good reception is found in the distance to the source too ) Is the loop quieter because of its magic design - or simply because it is 10 times further away (20dB) from the noise? OK for that. We get writers here who pound the table because their magic loop in the shack is noisy and their long wire 10M away in the back yard is quiet. They have to be told to turn off the flourescent light in the shack if they want their magic loop to work. (Their magic loop low score on Amazon) = (stupid.) Lesson one = learned. Thanks. Sebastien. |
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SWL for Newbies (was: Balcony Antenna for Shortwave Listening)
On Dec 13, 3:01*pm, Sébastien MEDARD wrote:
We get writers here who pound the table because their magic loop in the shack is noisy and their long wire 10M away in the back yard is quiet. They have to be told to turn off the flourescent light in the shack if they want their magic loop to work. * *(Their magic loop low score on Amazon) = (stupid.) Lesson one = learned. Thanks. Sebastien. One thing handy about a small loop is you can turn it to null out the offending noise. Like Richard says, there is no magical quality which provides lower noise vs any other antenna. The real benefit is being about to turn it, usually while in the listening position. If the loop is well balanced, the nulls are quite sharp and deep and in many cases you could make that nasty noise source vanish. You can also turn it to receive multiple stations that are on the same frequency. You null the one you want to get rid of. But these type of loops are best suited for the low bands. LW, MW are where they are best suited. You get much better nulls off a ground wave signal, than you do one that is propagated via skywave. So they tend to work better at nulls in the daytime vs at night. At night, you get a mix of ground and sky wave, and the nulls are not as deep. In the day, I can make most ground wave signals totally vanish by nulling them out. These can be used in the SW bands, but don't expect the deep nulls, being as most all SW will come via sky wave. For general SWL, you are usually better off with the various wire antennas. Random wires, dipoles, etc.. But I recommend a small loop for MW if you want the ability to null noise or undesired stations. Most of mine, I build from PVC tubing for the frames. I have one in this room that is a diamond, 42 inches per side. It's on a stand which allows it to rotate, and it stands almost as tall as the ceiling. But they don't have to be that big. I've got another round one that is about 16 inches across, and it works very well too. Just a tad less signal than the big one. But the s/n ratio is much the same for the majority of the stations listened to. http://home.comcast.net/~nm5k/loop5.jpg This is my usual favored method for building a low cost MW loop. The hardest part to come by these days is the variable cap. I dig them out of old radios, and old analog tuning stereo receivers. Those are some of the best ones to use, as they often have several gangs which can be wired in parallel for more capacitance, or deleted for less. For the upper tuning ranges of the loop, it's best to delete most of the gangs, and use one of the very small ones by itself. That way you get a smaller value, and will increase the upper tuning range, vs just turning all the gangs in parallel to the minimum setting. So I use switches to do this quickly. But if you can't find any old radios to acquire the variable caps, you can buy them online from a few places. I wouldn't use one any less than a dual 365pf BC cap. You can wire the two gangs together for 730 pf. With careful loop turn design, you can usually cover the whole MW BC band with one of those. But I prefer the ones out of old stereo receivers. They are even better, and can give a wider tuning range. I think the one on my big loop has four or five gangs, some being small and useful for upper end tuning, if the other larger gangs are switched out. |
#4
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SWL for Newbies (was: Balcony Antenna for Shortwave Listening)
On Mon, 13 Dec 2010 15:38:20 -0800, nm5k wrote:
On Dec 13, 3:01Â*pm, SĂ©bastien MEDARD wrote: One thing handy about a small loop is you can turn it to null out the offending noise. I should try small loops too. You get much better nulls off a ground wave signal, than you do one that is propagated via skywave. So they tend to work better at nulls in the daytime vs at night. At night, you get a mix of ground and sky wave, and the nulls are not as deep. In the day, I can make most ground wave signals totally vanish by nulling them out. That's an interesting concept. The difference between ground and sky waves and the way to use loops. And small loops are easier to make... Most of mine, I build from PVC tubing for the frames. A simple, but good idea. PVC tubing is inexpensive and quite rigid... I have one in this room that is a diamond, 42 inches per side. One meter... It is approximatively what I wanted to do at the beginning. It's on a stand which allows it to rotate, and it stands almost as tall as the ceiling. Do you tune it, or not? Is there a small loop inside or not? But they don't have to be that big. I've got another round one that is about 16 inches across, and it works very well too. Just a tad less signal than the big one. But the s/n ratio is much the same for the majority of the stations listened to. I definitively need to test them. http://home.comcast.net/~nm5k/loop5.jpg This is my usual favored method for building a low cost MW loop. The hardest part to come by these days is the variable cap. I got one and I am searching for others. It seems that variable caps are one of the center of a lot of things in radio reception ) I can see on the loop5.jpg image that you connected one wire to the ground and one wire to both other connections (double gang capacitor) so that you add the result of both capacitors. Is that correct? That way you get a smaller value, and will increase the upper tuning range, vs just turning all the gangs in parallel to the minimum setting. So I use switches to do this quickly. Exact. That sounds good. But if you can't find any old radios to acquire the variable caps, you can buy them online from a few places. I wouldn't use one any less than a dual 365pf BC cap. You can wire the two gangs together for 730 pf. That's the kind I get. With careful loop turn design, you can usually cover the whole MW BC band with one of those. But I prefer the ones out of old stereo receivers. They are even better, and can give a wider tuning range. I think the one on my big loop has four or five gangs, some being small and useful for upper end tuning, if the other larger gangs are switched out. I found a 500pF + 500pF one too, with a slow motion drive. Another way to drive them slowly is to get a 20cm (10 inches) piece of wood, perforate it on one side to put the capacitor axis into the hole (put some glue, but a smaller hole is better, and push it hard so that the axis enters inside the hole), and you get something that can be tune very precisely with one finger... About the piece of wood, the longer, the higher in precision tuning. Sebastien. |
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SWL for Newbies (was: Balcony Antenna for Shortwave Listening)
On Dec 15, 2:17*pm, Sébastien MEDARD wrote:
Do you tune it, or not? Is there a small loop inside or not? Yes for both. The cap is down at the bottom corner, and I use a separate coupling loop because I'm feeding coax to the radio. The 42 inch per side loop uses 5 turns on the main loop. The coupling loop is on the inside, and maybe 36 or so inches out from center. Sounds like you are in good shape for caps. That 500-500 would be good. I'd put a small mini switch between the two gangs to be able to cut or add the second gang. That's what I do on mine anyway. I solder the switches right to the tabs on the cap. I also have a handful of fixed caps to add if I want to drop further down into longwave. I don't use them that often so I just clip them on if needed. I think my 16 inch round loop has about 12 turns if I remember right.. It also uses a inner coupling loop. For me, those loops are mainly for AM-BC, but I do wander down and listen to the air beacons from time to time. And the big one covers 160 meters, so I use it for that sometimes. |
#6
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SWL for Newbies (was: Balcony Antenna for Shortwave Listening)
Hello,
On Thu, 16 Dec 2010 05:33:58 -0800, nm5k wrote: Yes for both. The cap is down at the bottom corner, and I use a separate coupling loop because I'm feeding coax to the radio. I saw a lot of photos where I saw the cap on the top and the coax feeded to the coupling loop on the bottom. Is doing the other way OK? The 42 inch per side loop uses 5 turns on the main loop. The coupling loop is on the inside, and maybe 36 or so inches out from center. Sounds like you are in good shape for caps. That 500-500 would be good. Great. I'd put a small mini switch between the two gangs to be able to cut or add the second gang. Definitively a good idea. That's what I do on mine anyway. I solder the switches right to the tabs on the cap. Good advice. I also have a handful of fixed caps to add if I want to drop further down into longwave. I don't use them that often so I just clip them on if needed. Planned. The thing that can be done is to use the same base board on the different loops to be used. Tell me your thoughts.... I was planning to put everything on a wood board... I think my 16 inch round loop has about 12 turns if I remember right.. It also uses a inner coupling loop. For me, those loops are mainly for AM-BC, It seems the size of the loop (I didn't play with loop software yet) is not critical, but is it possible to say that the lower band you want to listen, the taller loop you should use? but I do wander down and listen to the air beacons from time to time. And the big one covers 160 meters, so I use it for that sometimes. Well... Sorry for the newbie question.... But what do you mean by beacons? Sebastien. |
#7
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SWL for Newbies (was: Balcony Antenna for Shortwave Listening)
On 13 Dec 2010 21:01:30 GMT, Sébastien MEDARD wrote:
I understand better what is the purpose of this kind of map (on SDR- Radio.com software for example). Where you can see an OM, you are pretty sure to see this kind of map. Hi Sébastien, If you mean the "gray line" map - yes. When I used to teach RTTY there were only two tones. The reason why they call you OM ? ) Touché This will reveal the "Law of Diminishing Returns" (the more you add, the less you get back). Interesting. What would be the best ratio? You mean the best number of turns? Depending upon band, maybe as many as 6 to 10. One is good enough. There are many options to balance. One correspondent here, years ago (silent key), wrote extensively on this subject - google this group (or the internet) for Reg Edwards, G4FGQ. For instance, google the keywords in: RJELOOP1 * Performance of Transceiving, single-turn, magloop antennas of various regular shapes. RJELOOP2 * Performance of Transceiving, single-turn, magloop antennas of rectangular shape. RJELOOP3 * Analysis of receiving, multi-turn, square, loop (or frame) antennas, ELF to HF. I will try to find one when they are cheaper. Try: http://www.bookfinder.com/search/?au...ic&st=sr&ac=qr OK. But today we probably ask more to radios than yesterday, no? No, probably less. Being an OM, (40 years ago) I also taught classes for repair and maintenance of Collins' famous receiver, the R-390. EVEN NOW (40 years later), this is probably the best receiver for its price (and even two to three times its price). The real science of low noise is found in the distance to the source. Lapalisse would have said exactly the same thing. He would have said that the real science of good reception is found in the distance to the source too ) So, my comment was a lapalissade? Certainly. 73's Richard Clark, KB7QHC |
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SWL for Newbies (was: Balcony Antenna for Shortwave Listening)
On Mon, 13 Dec 2010 16:06:51 -0800, Richard Clark wrote:
On 13 Dec 2010 21:01:30 GMT, SĂ©bastien MEDARD wrote: I understand better what is the purpose of this kind of map (on SDR- Radio.com software for example). Where you can see an OM, you are pretty sure to see this kind of map. Hi SĂ©bastien, If you mean the "gray line" map - yes. There should free software displaying this gray line with UTC time, no? This will reveal the "Law of Diminishing Returns" (the more you add, the less you get back). Interesting. What would be the best ratio? You mean the best number of turns? Economics is interesting too RJELOOP3 * Analysis of receiving, multi-turn, square, loop (or frame) antennas, ELF to HF. Can be find here : http://www.zerobeat.net/G4FGQ/page3.html#S301 I will try to find one when they are cheaper. Try: http://www.bookfinder.com/search/?au...%27s+Receiving +Antenna+Handbook&lang=en&isbn=&submit=Begin +search&new_used=*&destination=us¤cy=USD&mod e=basic&st=sr&ac=qr I found the "Receiving Antenna Handbook" quite cheap, but the "Loop Antenna Handbook" is still expensive. Between $60 to $257... I will try the cheapest. OK. But today we probably ask more to radios than yesterday, no? No, probably less. Being an OM, (40 years ago) I also taught classes for repair and maintenance of Collins' famous receiver, the R-390. EVEN NOW (40 years later), this is probably the best receiver for its price (and even two to three times its price). Do you calculate that in constant dollar from the 50's? I can imagine the teaching class. Everybody with a Collin's in front of him/her... A one year project to restore completely one of this legendary radio. I would like that! With a good DSP outside (Audio DSP only), can beat every other ones? It seems not easy to get one, especially in Europe... The real science of low noise is found in the distance to the source. Lapalisse would have said exactly the same thing. He would have said that the real science of good reception is found in the distance to the source too ) So, my comment was a lapalissade? Certainly. You got the picture Sebastien. |
#9
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SWL for Newbies (was: Balcony Antenna for Shortwave Listening)
On 15 Dec 2010 20:52:22 GMT, Sébastien MEDARD wrote:
There should free software displaying this gray line with UTC time, no? Hi Sébastien, I'm sure there is - somewhere. GoogleEarth would be an elaborate tool to accomplish this. I found the "Receiving Antenna Handbook" quite cheap, but the "Loop Antenna Handbook" is still expensive. Between $60 to $257... I will try the cheapest. Myself, I would not advise spending more than $20. Professional antenna books barely give more than one section of the first chapter to its discussion. OK. But today we probably ask more to radios than yesterday, no? No, probably less. Being an OM, (40 years ago) I also taught classes for repair and maintenance of Collins' famous receiver, the R-390. EVEN NOW (40 years later), this is probably the best receiver for its price (and even two to three times its price). Do you calculate that in constant dollar from the 50's? Today's cost matched with the price of equivalent performance from an available vendor. I can imagine the teaching class. Everybody with a Collin's in front of him/her... A one year project to restore completely one of this legendary radio. I would like that! There were two to a radio. 40 to 30 hours learning the schematic theory of operation; and troubleshooting and tuning procedures and 30 to 40 hours in front of the radio. The class was 2 weeks long. Complete restore unnessecary, of course, as the last class had fixed any problem. No, we had a data bank of known problems, known solutions, and the time to debug them averaged over at least 100 students for each problem. With a good DSP outside (Audio DSP only), can beat every other ones? Good for filtering, probably tighter than the mechanical filters (theoretically), but there are many, many other considerations. It seems not easy to get one, especially in Europe... That seems like a very real impediment. And with it weighing in at 85 pounds (40 kilograms), the cost to deliver would add considerably. So, my comment was a lapalissade? Certainly. You got the picture In technicolor and 3D. 73's Richard Clark, KB7QHC |
#10
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SWL for Newbies (was: Balcony Antenna for Shortwave Listening)
Hello,
On Wed, 15 Dec 2010 15:40:31 -0800, Richard Clark wrote: On 15 Dec 2010 20:52:22 GMT, SĂ©bastien MEDARD wrote: There should free software displaying this gray line with UTC time, no? I'm sure there is - somewhere. GoogleEarth would be an elaborate tool to accomplish this. Well... In French we say that it is like using backhoes to move a bucket of sand... I found some software here : http://www.ac6v.com/software.htm#GEO Need to be tested... I found the "Receiving Antenna Handbook" quite cheap, but the "Loop Antenna Handbook" is still expensive. Between $60 to $257... I will try the cheapest. Myself, I would not advise spending more than $20. Professional antenna books barely give more than one section of the first chapter to its discussion. I totally agree, I will see what the seller proposes. I can imagine the teaching class. Everybody with a Collin's in front of him/her... A one year project to restore completely one of this legendary radio. I would like that! There were two to a radio. 40 to 30 hours learning the schematic theory of operation; and troubleshooting and tuning procedures and 30 to 40 hours in front of the radio. The class was 2 weeks long. Complete restore unnecessary, of course, as the last class had fixed any problem. No, we had a data bank of known problems, known solutions, and the time to debug them averaged over at least 100 students for each problem. With a good DSP outside (Audio DSP only), can beat every other ones? Good for filtering, probably tighter than the mechanical filters (theoretically), but there are many, many other considerations. I should try to see if there are any OM near the place I live. Could be interesting to see those old boxes. Well, many thanks for the basic information you gave me. Now, I need to use it. SĂ©bastien. |
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