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AM Frequency Of The Week - 620 kHz
- Thread starter W7PAT
- Start date
620 in south central Colorado: Grand Junction makes it in weakly daytime. At night the frequency is dominated by KMKI/Plano, TX, and used to be dominated by its predecessor, KWFT Wichita Falls. Also heard: Regina, KMNS/Sioux City, and KTAR/Phoenix.
Here in Altamonte Springs it's wdae day and night. I get spanish at night as well. Another question. I can hear 540 wflf blasting away on 620. Any ideas? I'll have to try and see if it happens away from my house.
How far away are you from WFLF's tower site? You're probably getting a harmonic of some sort.
I could get WTMJ in Genesee County even when it was 5000 watts nondirectional daytime. WATE/WETE/WRJZ was a frequently heard nighttime signal. WTMJ was sometimes heard at night, but not always.
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rbrucecarter5
Guest
I was going to guess a radio with the front end badly out of alignment.
Hello. I'm in Altamonte Springs FL. I have no idea how far that is from wflf's transmitter sight. I just bought a cc 2e radio and that radio has no 540 harmonics on 620.
Looks like you're about 20 miles from WFLF's site, which would likely be a little far for a harmonic....although it is 50kw on the low end of the dial, pretty much aimed right at you. Still, Bruce is more knowledgeable about this stuff than me, so you're probably better off with his diagnosis of the issue.
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rbrucecarter5
Guest
The thing that leads me to think of an alignment issue is the difficulty of producing an 80 kHz offset any other way. Assuming the radio has a tuned RF stage, either the antenna stage or the RF stage, or both could be off. Just a guess. It is really easy to miss, because some radios use pretty broad stages in the front end - you think the radio works properly because a lot of things come in, but in reality it isn't tracking.
I had the problem in an SRF-59. For some reason it went deaf as a stump. Even though it wasn't subjected to shock, dropped, got wet, or anything - one of those slug tuned transformers slipped a notch. I don't know when, I don't know how. I thought it had been zapped! But one turn of the transformer and the radio came right back.
Anything nearby around 700 or 1160 kHz?
Please let's keep the technical terms correct....a Harmonic is the primary signal multiplied....2x, 3x, 4x ,etc.....A signal on another channel that is not harmonically related is either a spurious emissions from the main signal source or due to a mix of other signals (intermodulation mixing distortion...or IMD or just plain intermod)
Could also be due to front end overload......a spectrum analyzer would show if 540 is clean or not....
Good luck with me on that.
I freely admit that I'm a doofus who leaves the technical stuff to guys who actually know what they're talking about. I'm just a guy who likes playing around with radios, and spent a decade in the industry (1970s) before getting into other media on a multinational basis.
. When I spent a year of high school in Honolulu, I lived two blocks from K-POI's studio and 5kw xmtr. In addition to their assigned frequency, 1380, I heard them all over the dial including several low shortwave bands on my Hallicrafters S-120. Harmonics or not, it all sounded the same to me. So with all due respect and apologies, I'll limit myself to what I hear and describe it or express my thoughts as best as I can, leaving the physics to you and guys like Schroedingers, Bruce, David, and the others here who are all smarter than me.
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rbrucecarter5
Guest
I am trying to figure out what combination of local stations could also mix with the LO and somehow produce an image of 540 on the dial at 620. The LO of the radio should be operating at 995 kHz. It might potentially have a second harmonic at 1440. But 1440 is also a local station. If it interacts with 1520, you would have 80 kHz. That would give the offset, but how it might be mixing it - I don't know. The point is - antenna and RF stages are not brick walls, anything down the slope in the stop bands will mix with the LO in the radio. And the LO might not be a perfect sine wave, if it has a second harmonic then you will get images of locals at strange places.
Which leads me to a potential solution to an issue of my own. My $31 Radio Shack wonder LW, SW, AM, FM radio I recently got on clearance has an interesting issue. There is no 540 here, but there is a 1520 that pumps out 25kW just a few miles up the road. I get an image of them right on 620 - so - 1520 minus 900 kHz and you get 620! That station is leaking into the LO of my radio and acting like a second LO frequency! I suspect your issue is similar. The slightest touch of alignment might get rid of it, or perhaps shield the LO better. My Radio Shack is pretty open layout inside: http://earmark.net/gesr/2000629.htm - see step 13. That is more space than I would like to the oscillator section. But I don't use it for AM, its strong point is FM.
I'm a couple miles away from the array of towers that broadcast both 970 WFLA and 1250 WHNZ.
During the day (but not at night) on my Sangean PR-D5, on most of the empty frequencies at the upper part of the dial I get splatter from WHNZ.
On the lower part of the dial, many empty frequencies have splatter from WFLA. In between 970 and 1250, it's WFLA splatter.
On my little Sony SRF-M37, it's the splatter of WFLA on some empty frequencies below 970 but above 970, I actually hear WFLA. On the dial above 1250, I can hear WHNZ but with the splatter of WFLA.
On my car radio, I don't get any of that.
During the day (but not at night) on my Sangean PR-D5, on most of the empty frequencies at the upper part of the dial I get splatter from WHNZ.
On the lower part of the dial, many empty frequencies have splatter from WFLA. In between 970 and 1250, it's WFLA splatter.
On my little Sony SRF-M37, it's the splatter of WFLA on some empty frequencies below 970 but above 970, I actually hear WFLA. On the dial above 1250, I can hear WHNZ but with the splatter of WFLA.
On my car radio, I don't get any of that.
There is a certain limitation to selectivity in terms of "dB down" from the radiated frequency. If you have a 1 V/m signal, the blanketing contour, and this limit is 60 dB down, you essentially have a 1 mV/m apparent signal at the frequency you are hearing it on. If it is 66 dB down, you have an apparent 0.5 mV/m signal. I notice this on many newer radios, but few old radios. The harmonics, images, and RITOIE (yes this can happen on AM too, but with fewer stations oddly spaced, you hear it less) tend to be on discrete frequencies.
The radio's an updated ATS505, schematic is available online for the original (they use a different AF chip on the Radio Shack World Receiver than they did on earlier 505's -- maybe new ATS505's have them also).
As you probably figured out (I just looked at your tech page) the SW goes through a separate RF amp transistor, but the MW section runs into the IF chip similarly to your average boombox or clock radio.
Mine has great selectivity on MW, for some reason (maybe the ceramic filter is a good one). I have no overload issues on MW on mine, but I'm in a low signal area. Works well with an external loop. I was able to DX some weak adjacents with the 20-629 I couldn't with some of my other radios (Superadios, TRF, DX-375, etc.).
PS -- on your tech page you mention the MW performance might be impaired because of the short loopstick. I'm wondering if it isn't something else. I have other Sangean / RS radios with similar sized loopsticks that are hotter on MW (sensitivity wise) -- including the DX-350's, which circuitry wise aren't much different from a boombox / clock radio on MW -- just the antenna going into the IF chip through the standard coils & stuff (i.e., no external RF amp).
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rbrucecarter5
Guest
I patched in a 200 mm loop antenna and AM was as good as any non-tuned RF radio I own. But there isn't really room in the case for a bigger ferrite bar, and the LW coil is a problem. So I left it stock. It's strong point is FM - with the narrow ceramic filters it is better than any other portable I own.
If you have a link to the schematic of the other radio, I would be grateful.
If you're still into DXing try it with an external loop, yours might have the same selectivity mine does. Narrow skirts, cuts out a lot of the splatter. The only two radios I have that seem to match or out do it in reducing splatter is a DX-370 and the PR-D5.
I'll look and see if I can find the link, or possibly could PM it to you. It's the ATS-505 service manual. You might be able to find it using google, which is what I did. I think it was a Russian radio enthusiasts site.
I doubt they changed the circuitry from that on the schematic, so you'd probably find it helpful.
What I noticed was that the AF chips are different. Also the radio tunes differently than I see it described on EHam. Mine doesn't chuff. You can hear the stations cut in when tuning up the band, but no chuffing. When I tune across empty portions of the SW band, it sounds just like analog. They may have updated the firmware.
EDITED TO ADD:
I think it may be this link. It seems to match the one on my computer. It says diagram, but it's actually the service manual.
http://www.radioscanner.ru/files/sangean/file188/
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Would thickness of a loopstick also affect gain? My World Receiver 20-629's loopstick measures as 120mm long, 7mm thick. On my DX-350, which is hotter on AM barefoot, the loopstick is also 120mm long, but the loopstick is flattened on the sides, and it's 8mm thick instead of 7mm. I'm wondering if that's enough to make a difference.
The radios have different IF chips, of course. The 350's CXA1019 has a built in "AM front end" -- maybe that makes the difference. I'm not sure if the 20-629's IF chip (TA2057) has an RF amp or front end, although from the pin diagrams on the datasheet, it looks like it has one.
The radios have different IF chips, of course. The 350's CXA1019 has a built in "AM front end" -- maybe that makes the difference. I'm not sure if the 20-629's IF chip (TA2057) has an RF amp or front end, although from the pin diagrams on the datasheet, it looks like it has one.
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