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Why do some AM stations sound OK on SSB and others (mine) do not? You technical experts don’t be shy, lay on the theory. I assume it is an issue of signal quality?
Why do some AM stations sound OK on SSB and others (mine) do not? You technical experts don’t be shy, lay on the theory. I assume it is an issue of signal quality?
I was listening to my Talking House transmitter with my communication receiver. Normally I listen to MW BCB in AM of course, but switching to USB or LSB on my station it sounds terrible. Well to be expected I thought, then I listen to commercial BCB MW stations on SSB and they sound OK; the quality of the audio went down to be sure, but it was semi-listenable. With my signal USB/LSB sounds very garble.
Total posts : 45366Mine is the same way and here’s why.
The Commercial Stations are farther away,
allowing the carrier to weaken some.
Your transmitter is so close that the carrier is really strong.
Thus garbling the audio in SSB, usually with a high pitch or low pitch squeal, pending how close you are to the carrier frequency.
Total posts : 45366You can simulate station distance by adding attenuation on the communications receiver, or padding the input with external attenuators if there is none on the receiver.
SSB, upper or lower, is a form of AM transmission without the carrier. Only the side bands are transmitted. It is the receiver that “replaces” the carrier locally.
RFB
Total posts : 45366I get this too when I switch my sony 7600gr to SSB.
It sounds like crap, but I am about 2 feet away from the antenna.
Was it just me, or did everyone’s station sound really good today?
I drove out to get groceries and my signal was really getting out there.
Geoff
Total posts : 45366Hi Geoff:
What were the conditions during the excellent reception. Snow still on ground? Ice? Moisture? Sunny? Time of day?
The snow and ice did wonders here in Missouri, and now the ground is skwishy wet and also seems to propagate very well.
Total posts : 45366A wet ground will make them flea power signals reach double if not triple the normal distance. This is why its good to always keep your ground system on your Part 15 antenna system watered good like a field of carrots. 😀
Seriously the water increases the ground conductivity and since LW/MW/SW are ground hugging signals…it stands to reason why those distant stations come in like a wild herd of bison….making a stampede over anything in its way!
RFB
Total posts : 45366Mostly just Sunny and beautiful here on the east coast. A lot of snow must have been melting, making the soil and ground wet as well, went up to 72 degrees here in Baltimore!
Total posts : 45366Various models of the Talking House (mainly older ones) suffer from frequency instability. That is to say, the audio “pulls” the carrier frequency, resulting in simultaneous FM and AM of the carrier. If the FM component isn’t excessive, you’ll hardly notice this on a regular envelope detector AM receiver, but it sounds horrible on SSB because the audio will change pitch with modulation.
I’m sure there’s a power supply related fix for this, but my TH doesn’t do it so I can’t say where the problem might be occurring. But if you’re an engineer, I would look at the supply line to the synthesizer and VCO and see if the voltage changes with modulation.
Total posts : 45366Might have something to do with it,.
Total posts : 45366I agree with WEAK on this one except that they all do it,even the 5.0 !!! Even without modulation ! That is why the TH sounds so bad when there is any heterodyne in the background whatsoever,it warbles. The carrier warbles all by itself, I suspect due to poor PLL design. It has nothing to do with signal strength or power supply.
I even tried to add some internal filtering to the supply rails,didnt help at all. You can change the frequency by pushing on the top of the chassis,a definate sign of a poor design.My SSTran is rock solid,no warble and is perfectly copyable on any SSB reciever and is very listenable with slight heterodyne interference.
Hmmm,maybe I could marry the two and have the best of both…..nah.
Total posts : 45366Well, the faults I was having with mine went away when I switched to a Hewlitt-Packard printer PS. The signal has been basically the same, the things that affect it are relatively predictable. With daily variances, of course, it gets noise at less distance out when there are T-storms within 60 miles, and of course skywave interference after dark, plus when pulling into a space in front of a store, transformers and boosters on above ground power lines, rain, the amount of auto traffic downtown, etc.
I can tell, often just by looking at the sky, what I can expect. Otherwise, the signal has been extremely stable for me. ‘Course I spent what many might consider an inordinate amount of time going for perfect peak over a period of three days, and in variable conditions. In the end there was almost no tolerance … only one spot got max resonance in all conditions.
I think TH transmitters are not all the same, regardless of model. I believe the place where they are manufactured is not particular about components, they go for the least expense and delivery timeliness, meaning that quality can vary from batch to batch. I got a good one that I’m using, but another one exactly the same model is just flat different, doesn’t sound the same, doesn’t tune quite the same.
Of course midband AM ground wave is improved by an increase in ground conductivity, so the wetter-the-better. If you have a small yard, the signal should be improved not only by shallow buried ground radials, but also by the quality of the soil. IOW, if you take good care of your yard, it should help.
Total posts : 45366When I originally critiqued the TH some time ago, I mentioned the “warble” that was obvious when another weak station was on the same frequency. I decided it was most likely instability in the PLL.
I installed a trimmer capacitor across the PLL oscillator crystal to NET it on frequency. The transmit frequency was about 800 Hz off frequency and now I can hold it to within a couple cycles.
Since I have done this, the “warble” seems to have disappeared. I’m not sure if one is connected to the other but it sounds fine now.
There were already a couple through holes on the PCB and they go to either side of the crystal so the mod was easy to do. It’s almost as though they planned for it and didn’t put it in.
The cap I used is an air-variable PC mount, 10 to 160 pf.
Total posts : 45366Usually the cause to PLL warble is the inadequate filtering in the PLL loop circuit causing the PLL to bleed in enough to frequency shift or modulate the carrier. This can be observed on a spectrum analyzer or even an o-scope capable of direct measurement of the carrier in question.
I call it PLL PING. Basically that is what its doing..pinging the carrier to heavy thus causing the “warble”.
RFB
Total posts : 45366Thanks Carl and RFB – I did not realize ground conditions had such an affect. That might explain the fact my range varies from 140-160 feet. My antenna hangs from 2nd floor window on the back of my vinyl sided house. From my back yard I can walk straight east, all over grass, into the adjacent green space which ends at the street about 160 feet away from the antenna. The strong reception ends about 160 feet where the grass/dirt ends and street and shrubs meet. From what you say that makes sense. Some times I only get about 140 feet, and now to think of it, that jives with dry ground.
Mighty1650 and RFB – I tried attenuation, switching my communication receiver to a crippled antenna. No big difference, but walking away from my house with my portable MW/SW/FM Degen DE1103, both commercial and my station sound cruddy on SSB, with the portable. The difference is not that great, but the edge still goes to the commercial station. The PLL warble mentioned is heard on the portable MW/SW radio. That is the function of the DE1103. The communication receiver I have is a TenTec RX320D with excellent SSB.
WEAK-AM & Ken Norris – I think some TH vary from one to another, even with in the same model. I bought four TH 5.0’s last year used (new) on iPay. I sold three, kept one. They were all the same. I found they were all the same at the time. I did not know enough to test them as much as I wish I would have before selling them. One of the guys who bought a TH unit from me has more output than mine, measured on the scope with 50 ohm load. Mine is not shabby power wise. Lets say it makes a full 100 mw at 1700 Khz. ; ) I am not sure how much they vary, but it seems credible folks say so. I think there is some truth to it.
Power supplies: I tried the TH on the laptop power supply, and it made no difference. I did not have a lot of time so I have to check it again. When I first got my TH (actually four of them) I tried one switching power supply and three linear power supplies. I did this to track down a hum issue. The one I use now is the small switching wall wart I bought as a replacement from Talking House. TH sells switching power supplies for their TH radios now, at least as replacements. The original linear TH power supplies are big wall warts with grounded three prong plugs. I suspected it was a ground loop “hum” maker. The switching power supply was an improvement! I sold the linear power supplies with the extra TH units I bought, so I don’t have a TH linear power supply to test. I put the TH switching power supply on the scope. It runs at about ~570 Hz and has about ~40 mV saw tooth ripple (unloaded). My laptop power supply has 20 mV of pure hash. Not sure which is worse? I read some one mounted a high quality switching supply inside the unit and got rid of their hum issue. It may help the PLL by just having more power available?
WEAK-AM and RFB – with the portable MW/SW SSB radio I can hear the PLL warble. You can’t hear the warble on the TenTec RX320D (which is a better receiver). WEAK-AM do you have any pictures or detailed description of the mod you made. It sounds simple a variable air cap across the PLL crystal, which I assume is the small tin can near the antenna tuning mechanism. What you are saying is the displayed Freq is not longer accurate or shifted from indicated with this mod? If you can give any details about how to “tune it” and installation that would be great. Will this mod make a difference to “normal” AM reception. I am satisfied with the sound for now.
Total posts : 45366Well,I already have a trimmer added there,and it does net better-to a point. You can change the pll loop by waving your hand around anywhere near the circuit,it warbles a lot more…or less!!! When I place my hand just right and hold it perfectly still,it stops and sounds clean even on SSb. Put the cover back on and it all goes to hell. Maybe it needs a grounded shield around key components to stabilize them better….again I must say its a poor design. I also noted any movement of the antenna,say like in a windstorm,also makes the PLL move around. It’s no wonder they were blowing these out at $99 !
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