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#11
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FM radio reception at ~24MHz?
dave wrote:
Now you get to experience the joy of building a crude preselector. A 20 dB pad might work, try that first. A friend of mine made one with a coax stub, and a T connecter. I'll ask him the length and type of coax. Geoff. -- Geoffrey S. Mendelson, N3OWJ/4X1GM/KBUH7245/KBUW5379 |
#12
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FM radio reception at ~24MHz?
On Tue, 18 Mar 2014, Geoffrey S. Mendelson wrote:
dave wrote: Now you get to experience the joy of building a crude preselector. A 20 dB pad might work, try that first. A friend of mine made one with a coax stub, and a T connecter. I'll ask him the length and type of coax. Wouldn't that have been a notch filter, to get rid of a particularly strong and pesky specific signal? If it's just one station, then it is a solution, set and forget. But if there are multiple stations causing problems, then more is needed. I was going to say in the old days endless preselectors and tuners and preamps were built (and even sold as commercial products) in an attempt to boost the performance of a lot of those low end receivers. I remember one mod for the Hallicrafters S38 that was just one tube, no tuned circuits, the performance boosted because the tube meant the existing tuned circuit wasn't loaded down. There'd be low pass filters to get rid of FM and TV stations, high pass filters to get rid of AM broadcast stations, and just things to peak up specific frequencies to get rid of images. I don't think any of that would have helped my Hallicrafters S-120A (the transistor model), that thing didn't need an antenna to receive endless local broadcast stations. It would have needed a lot of work with shielding to make a filter between the antenna and receiver useful, it wsa just picking up the signals directly. Sometimes it is a too strong local signal, sometimes it is a badly designed receiver that will never be fixable. Michael |
#13
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FM radio reception at ~24MHz?
On Tue, 18 Mar 2014 14:00:53 -0400, Michael Black wrote:
I don't think any of that would have helped my Hallicrafters S-120A (the transistor model), that thing didn't need an antenna to receive endless local broadcast stations. It would have needed a lot of work with shielding to make a filter between the antenna and receiver useful, it wsa just picking up the signals directly. That was my first receiver, my Mother got it from Sears for about $70. That model was terrible, it looked cool, but it was a real dog. I finally got an older Hallicrafters, SX-40 I think, and it was much better. |
#14
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FM radio reception at ~24MHz?
On Tue, 18 Mar 2014, sctvguy1 wrote:
On Tue, 18 Mar 2014 14:00:53 -0400, Michael Black wrote: I don't think any of that would have helped my Hallicrafters S-120A (the transistor model), that thing didn't need an antenna to receive endless local broadcast stations. It would have needed a lot of work with shielding to make a filter between the antenna and receiver useful, it wsa just picking up the signals directly. That was my first receiver, my Mother got it from Sears for about $70. That model was terrible, it looked cool, but it was a real dog. I finally got an older Hallicrafters, SX-40 I think, and it was much better. I emptied out my bank account of accumulated birthday and Christmas money, and some other money was added. It was more like $90 Canadian, which was a lot for me at the time, but the cheapest receiver I could get locally, and probably the cheapest I could get generally. How many people were suckered in by those low end receivers? We had no experience, and as you say, it all looked so good. The dial was awful, but hey, it had all those places around the world stencilled, I could get Antarctica if I tuned to that spot there. I was still a beginner, so how would I know about seeking out a local ham club to see if I could at least find the same level of receiver for less money on the used market? It didn't even take that many months for me to get up to speed, but I spent the money then, rather than waiting. I was lucky, a year later when I got my ham license, someone lent me (for a decade) a Hammarlund SP-600, which wasn't perfect, but it was almost infinitely better than that S-120A. I probably could have kept the Super Pro, but at one point when I wasn't using it much, he asked if he could take it back to lend to someone else. A couple of years ago, a 1950s Hallicrafter ad was making the rounds on the internet, and that reminded me that Hallicrafter did seem to play up that aspect, the foreign countries, and the exotic world out there. Hallicrafters sold a record for some time as part of their advertising, only 25cents. WHen I remembered seeing those records in their ads, I did a search, and it's online, though I don't have a specific URL. I was 11 years old when I got that S-120A, all that exotic stuff and exotic countries I could hear with it was part of Hallicrafter's promotion, and certainly was a lure to me, when the reality was, those low end receivers werne't likely to get much more than the strongest of foreign broadcasters. At the same time, that past is gone. I think I'd rather have the illusion of it, the hope that it could happen, than being older and the world a lot smaller, and that exotic world completely gone. Michael |
#15
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FM radio reception at ~24MHz?
On 03/18/2014 05:39 AM, Joe from Kokomo wrote:
A great tutorial / construction article on how to use the dongle as a DC to daylight software defined radio (SDR): QST magazine, January 2013, pp 30-35. If you know a member of the ARRL, they can print a copy of this article. Interesting article, thanks for posting that, Joe. Jon |
#16
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FM radio reception at ~24MHz?
On 03/18/2014 11:00 AM, Michael Black wrote:
On Tue, 18 Mar 2014, Geoffrey S. Mendelson wrote: dave wrote: Now you get to experience the joy of building a crude preselector. A 20 dB pad might work, try that first. A friend of mine made one with a coax stub, and a T connecter. I'll ask him the length and type of coax. Wouldn't that have been a notch filter, to get rid of a particularly strong and pesky specific signal? If it's just one station, then it is a solution, set and forget. But if there are multiple stations causing problems, then more is needed. I was going to say in the old days endless preselectors and tuners and preamps were built (and even sold as commercial products) in an attempt to boost the performance of a lot of those low end receivers. I remember one mod for the Hallicrafters S38 that was just one tube, no tuned circuits, the performance boosted because the tube meant the existing tuned circuit wasn't loaded down. There'd be low pass filters to get rid of FM and TV stations, high pass filters to get rid of AM broadcast stations, and just things to peak up specific frequencies to get rid of images. I don't think any of that would have helped my Hallicrafters S-120A (the transistor model), that thing didn't need an antenna to receive endless local broadcast stations. It would have needed a lot of work with shielding to make a filter between the antenna and receiver useful, it wsa just picking up the signals directly. Sometimes it is a too strong local signal, sometimes it is a badly designed receiver that will never be fixable. Michael The MFJ-956 passive pre-selector is in my tool kit. They also make several actives. They all cover HF, which includes 24 MHz. |
#17
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FM radio reception at ~24MHz?
dave wrote:
The MFJ-956 passive pre-selector is in my tool kit. They also make several actives. They all cover HF, which includes 24 MHz. In the opposite direction, you can google or search on eBay for an FM TRAP. Geoff. -- Geoffrey S. Mendelson, N3OWJ/4X1GM/KBUH7245/KBUW5379 |
#18
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FM radio reception at ~24MHz?
On 03/19/2014 07:19 AM, Geoffrey S. Mendelson wrote:
dave wrote: The MFJ-956 passive pre-selector is in my tool kit. They also make several actives. They all cover HF, which includes 24 MHz. In the opposite direction, you can google or search on eBay for an FM TRAP. Geoff. I probably have a bunch somewhere from my UHF TV years. I'm on the back side of Mt. Wilson and RF levels are weak enough that I can get away with scanner antennas and everything. I'd try the Pads first; get the dingus into its linear operation range. |
#19
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FM radio reception at ~24MHz?
On Tue, 18 Mar 2014 22:36:00 -0400, Michael Black wrote:
snip At the same time, that past is gone. I think I'd rather have the illusion of it, the hope that it could happen, than being older and the world a lot smaller, and that exotic world completely gone. Michael You are so right, Michael. The illusion, the sitting up all night on Friday and Saturday night, with headphones on, being about 12-17 years old, hoping for that illusive foreign station, the dial light glowing, my pencil and pad waiting for something to copy and to send off for a QSL! Now, my wireless radio will pick up all the stations I want, all over the world, just like a local. I still have my restored Lafayette SWL receiver, a big brother look a like of the S-38. I turn it on every once in a while, hook up a wire antenna, and relive the past. There is not much there anymore, but still can MW DX a lot! Here in Texas, it will pick up both coasts pretty well. I had an old ham repairman wire it to accept a Heathkit Q- Multiplier that I also have. With that, and the bandspread, and the IF/ RF amplifier, it works very well! |
#20
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FM radio reception at ~24MHz?
sctvguy1 wrote:
You are so right, Michael. The illusion, the sitting up all night on Friday and Saturday night, with headphones on, being about 12-17 years old, hoping for that illusive foreign station, the dial light glowing, my pencil and pad waiting for something to copy and to send off for a QSL! Now, my wireless radio will pick up all the stations I want, all over the world, just like a local. I remember that well too. When I was a teenager someone had a Normande (probably spelled wrong) AM/FM/Shortwave radio they dropped and it broke in half. I was able to get it working, and using various things such as my bed frame, the telephone line, etc, I was able to receive SW signals in a "garden" (basement) apartment. Before that I had something, but I don't remember what, maybe a 5 or 6 tube "all american special" with some SW coverage. I used that until around the time I turned 18, and was given an S-38B. Unfortuantely I gave that away in my 30's when I started buying "real" shortwave radios. I bought one of the first ICF-2010's in the US, brought in a few months early from Japan. When I got married in 1989, my wife had one too, and we kept hers, being a few years newer. My current shortwave radio is a Drake SPR-4, although I have a TR-7 "in the works". I still have my restored Lafayette SWL receiver, a big brother look a like of the S-38. I turn it on every once in a while, hook up a wire antenna, and relive the past. There is not much there anymore, but still can MW DX a lot! Here in Texas, it will pick up both coasts pretty well. I had an old ham repairman wire it to accept a Heathkit Q- Multiplier that I also have. With that, and the bandspread, and the IF/ RF amplifier, it works very well! I sure miss mine. MW DXing here is worthless because of the high noise. Although in a previous apartment I was on the edge of a nature preserve, and with a sheilded MW loop on the fence and the SPR-4, was able to receive the BBC station on 648kHz, about 3,000 miles away. Geoff. -- Geoffrey S. Mendelson, N3OWJ/4X1GM/KBUH7245/KBUW5379 |
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