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#1
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Chances are it is an image signal beacause RHC is broadcasting then.
The combination of a modestly priced but very sensitive receiver and big antenna means you are probably getting repeat signals all over the dial. Because the 350 is an analog receiver with a digital display my guess is that the receiver is actually tuned to 1700 +- 10. Try listening to these RHC frequencies to see if the signal is the same. 6000, 6060, 9550, 11760 It's a nice radio in many respects, but it has limitations that are a fuction of it's price. More than one review I have read complain about multiple images, poor dynamic range, etc. Get rid of that long antenna and use the RF gain to control signal strength. Honus wrote: It's Sunday here in Seattle, 0530 UTC and I'm picking up Radio Havana Cuba on a Grundig S350 with a 70' random wire antenna tuned to ~1697 KHz. (The signal drifts a tiny bit, between 1696 to 1698.) I've tried to do my own research and see if perhaps they broadcast on MW as well as SW, but I can't find any indications that they do. They're also frequently mentioning that it's a shortwave broadcast...so through what bit of electronic inadequacies on the part of Grundig am I hearing this on MW? I understand images to a degree, thanks to r.r.s. Is this a related issue? Thanks in advance. |
#2
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#3
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Honus wrote:
And now I'm hearing a memorial to Gene Scott on 1615 (MW, of course) at 0555 UTC. It's identical to the broadcast that I'm receiving clearly on 5755 (KAIJ, TX) You're receiving the 5755 transmission on 1615 because of the third harmonic of the radio's local oscillator. (i.e. they are NOT actually transmitting on 1615) When you tune to 1615, the radio tunes an internal oscillator to 2070KHz. This 2070KHz signal is mixed with the 1615KHz signal (if there was one). You get four outputs: 1615, 2070, 2070+1615=3685KHz, and 2070-1615=455KHz. The selective circuits in the intermediate frequency amplifier only pass the last signal at 455KHz, and that's what you hear. But the internal oscillator is not perfect. It generates "harmonics" on multiples of the frequency to which it's tuned. 2070KHz, 2070x2=4140KHz, 2070x3=6210KHz, 2070x4=8280KHz, etc... (they get weaker as the multiplier increases) If any of these multiples can mix with a signal to generate 455, then that signal will be heard as well. And in this case, it can. 6210-5755=455. The KAIJ signal will mix with the 3rd harmonic and will be heard. Your reception of Cuba on 1697 is probably from the same phenomonon. I note that when tuned to 1697KHz, the local oscillator is on 2152KHz. 2152x3=6456, and 6456-6001=455. So if Radio Havana was broadcasting on 6001KHz, you'd hear it on 1697. Monitoring Times does list Radio Havana as being on 6000KHz at 0530z. -- Doug Smith W9WI Pleasant View (Nashville), TN EM66 http://www.w9wi.com |
#4
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That's the preselector I believe. Yes, it could help, although in my
experience just reducing the antenna size will help too. Those little radios usually work pretty well on the whip alone. |
#5
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![]() wrote in message ups.com... Chances are it is an image signal beacause RHC is broadcasting then. The combination of a modestly priced but very sensitive receiver and big antenna means you are probably getting repeat signals all over the dial. Because the 350 is an analog receiver with a digital display my guess is that the receiver is actually tuned to 1700 +- 10. Try listening to these RHC frequencies to see if the signal is the same. 6000, 6060, 9550, 11760 It's a nice radio in many respects, but it has limitations that are a fuction of it's price. More than one review I have read complain about multiple images, poor dynamic range, etc. Get rid of that long antenna and use the RF gain to control signal strength. I've heard the same reviews. Now I actually know what they mean. g The long antenna really helps, though; I'm loathe to give it up. |
#6
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![]() "David" wrote in message ... An MFJ-956 between the radio and the antenna may help. I'm going to have to look into that. I'll dig through google as well, and see what the other denizens of r.r.s. have had to say about it. Thanks. |
#7
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![]() "Doug Smith W9WI" wrote in message ... Honus wrote: And now I'm hearing a memorial to Gene Scott on 1615 (MW, of course) at 0555 UTC. It's identical to the broadcast that I'm receiving clearly on 5755 (KAIJ, TX) You're receiving the 5755 transmission on 1615 because of the third harmonic of the radio's local oscillator. (i.e. they are NOT actually transmitting on 1615) I suspected as much, but the coincidence of the harmonic coming in so close to one of their other broadcast freq's made me wonder a bit. That and the fact that I've never picked up harmonics from SW in the MW end of my dial. I usually come across them 910 KHz away from the true frequency. Thanks for all of your help explaining this to me. I snipped it in this reply, but I've saved in my mailbox and I'll be sure to study it in more depth. |
#8
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Are you actually hearing more stations with the longer antenna? If so
make sure you are not dxing images (I've done it!). If the signals are just louder I would disconnect the antenna and increase the volume. The MFJ preselector could also help, although it might cost as much as the radio. |
#9
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Honus wrote:
It's Sunday here in Seattle, 0530 UTC and I'm picking up Radio Havana Cuba on a Grundig S350 with a 70' random wire antenna tuned to ~1697 KHz. (The signal drifts a tiny bit, between 1696 to 1698.) I've tried to do my own research and see if perhaps they broadcast on MW as well as SW, but I can't find any indications that they do. They're also frequently mentioning that it's a shortwave broadcast...so through what bit of electronic inadequacies on the part of Grundig am I hearing this on MW? I understand images to a degree, thanks to r.r.s. Is this a related issue? Thanks in advance. When your S350 is tuned to 1697.666666666..., the local oscilator is running at 2151.66666666.... RHC on 6000 kHz is mixing with the 2nd harmonic of the local oscillator (which is at 4303.3333333...) 6000 - 4303.333333... = 1696.6666666... It's a common problem with cheap portables. -- Mike Westfall, N6KUY, WDX6O Los Alamos, NM (DM65uv) Online logbooks at http://dxlogbook.gentoo.net Remove the Reptile to Reply |
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