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AM transmission - All the energy is in one of the sidebands

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GW8LJJ

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AM transmission

My homebrew transmitter (4-125 valve) is transmitting using plate and screen modulations and pushing out around 100 watts carrier. However, at the receive end It is noticed that only one sideband along with the main carrier is received. All the energy is in one of the sidebands only. Any suggestions at what could cause this?
 

Re: AM transmission

I would not believe this report unless the person has a spectrum analyzer. Great expense and effort was done in the 1950s to produce one sideband. I do not think that the gods are smiling on you.
 

AM transmission

Ha! Yes, but I can assure you that my transmitter is producing the carrier and the modulation is dominant in one of the sidebands. It cannot be seen on my spectrum analyser becaue, although it covers the band (80mtrs) it does not have the resolution to be able to see the sidebands! However, at the receiving end there are several that have the software defined radios that does have that resolution.
 

AM transmission

It may be the case, that you have an unusual high Q LC tank, or antenna matching filter. But simply tuning it to the carrier should remove any sideband unsymmetry.

As another explanation, the same buggy SDR may be utilized at the receiver sites.
 

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    GW8LJJ

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AM transmission

Try receiviing from some other receiver and then check. Coz it is practically not possible to produce single side band with a AM transmitter. Good luck.
VU3BEP
 

AM transmission

All noted.

FvM: That probably is the correct answer to the problem.

VU3BEP: This has been received on three different SDR receivers at different QTHs. It's not quite SSB as I am also radiating the carrier. It's just that the modulation energy is predominant in one sideband.

Flatulent: Perhaps I should patent it!
 

Re: AM transmission

With carrier and one sideband there will be a FM component. See if the receiver set to FM demodulation has an output.
 

AM transmission

Flatulent.
I am waiting for an SDR so that I can see the results for myself. I don't have FM demodulation on any of my HF receivers. To make adjustments without monitoring is just working blind of course. I am only guided by very well authorised personel at the receiving end. Although this is happening on my home-brew TX appaently this sort of problem has also been witnessed on a commercial TX.
 

AM transmission

If these are long-distance observations, can frequency selective fading give an explanation?
 

AM transmission

FvM: No, they are all from locals (all within 15miles straight line).

Pranam77: Something different. I also design and manufacture PCBs, double-sided for hobby small runs etc. I have a few questions. Can I contact you direct or would you prefer via forum? Thanks.
 

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