Hi Rik and LF
 
In Jim's case he has two sidebands indicative of AM modulation and you are right they are about 30 odd dBs down on the carrier. Not too bad suppression by 1950's standards.... hee hee. Where only one side band is reported on the data base is probably becuase the reporting station is having the  (say) lower side band clipped by having a slightly high dial frequency offset.
 
I have some JPEG files for the test we did yesterday if you would like to see them I will send off reflector. You may see something that could help Jim solve this issue.
 
73 petefmt

--- On Wed, 18/11/09, Rik Strobbe <[email protected]> wrote:

From: Rik Strobbe <[email protected]>

Subject: Re: LF: Re: G7NKS sidebands

To: "[email protected]" <[email protected]>

Date: Wednesday, 18 November, 2009, 8:58

Hello Jim, LF group,

I have noticed "double receptions" of my WSPR signal from a number of

stations. When it occurred the ghost signal was always 100Hz higher

and was 33-36dB weaker.

As the frequency shift and signal strength difference was the same at

the different RX stations I conclude that the cause was with me.

I think that it is just some AM modulation in the PA caused by the

100Hz ripple of the PSU.

73, Rik  ON7YD - OR7T

At 02:13 18/11/2009, you wrote:

>Dear Jim LF Group,

>

>Looking at the sidebands on the G7NKS WSPR signals, mains hum or other noise

>by itself is not a sufficient explanation of what is seen. Simply adding

>50Hz, 150Hz, etc. noise into the PC audio channel, then feeding the result

>into an SSB TX would give unwanted CW at frequencies offset from the SSB

>carrier frequency by +/-50Hz, 150Hz and so on, i.e. with the carrier "dial

>frequency" at 502.4kHz, unmodulated carriers would appear at 502.45kHz,

>502.55kHz and so on, in addition to the WSPR signal at around 503.9kHz.

>However, these would probably largely be removed by the SSB filter in the

>rig. Instead, we see unwanted sidebands offset from the wanted WSPR signal

>frequency by +/- 50Hz, 150Hz, with identical modulation to the wanted

>signal. This requires some sort of non-linear process to cause the

>intermodulation between the presumed mains noise and the WSPR signal

>somewhere in the TX chain.

>

>One possibility is that intermodulation occurs in the PA. Jim's description

>suggests that he is persuading the HF PA in the IC735 to produce output at

>500k. At this frequency, the PA linearity may well be poor due to the

>impedance matching, coupling, decoupling and feedback components in the PA

>being wrong for the frequency, and high flux densities occuring in ferrite

>components due to the low operating frequency. But this wouldn't explain why

>Jim also gets multiple received signals from a strong station with a clean

>signal, which implies some identical noise source and distortion in the

>receive path. It would also mean the mains noise getting through the

>filtering in the rig somehow.

>

>A possibility that would explain the unwanted sidebands appearing on both TX

>and RX signals is if one of the oscillators in the system has mains noise

>sidebands. The sound card clock seems unlikely, since this is just a simple

>crystal oscillator. I see the IC735 has some sort of multi-loop PLL

>synthesiser, which would certainly be prone to this type of spurious signal,

>since any kind of mains noise getting in would modulate the VCO frequencies,

>and would probably be the same on transmit and receive. This could be

>checked by receiving a clean carrier somewhere around 500kHz, and examining

>the audio output using Spec Lab or Argo or similar to see if 50Hz and 150Hz

>sidebands are present on the received audio tone.

>

>Cheers, Jim Moritz

>73 de M0BMU

>

>

>----- Original Message -----

>From: "James Cowburn" < [email protected]>

>To: < [email protected]>

>Sent: Monday, November 16, 2009 8:26 PM

>Subject: LF: rule #2 - assumption is the brother of all foul ups

>

>

> > LF

> >

> >

> >

> > Sidebands are back!  I think its caused by my TX getting hot and bothered

> > by

> > struggling at 500.  From cold it txs 50 watts but this soon drops back to

> > around 35, and the sidebands appear.  My sigs are better so having the

> > txfr

> > outside the shack and at the antenna is a vast improvement, but I now need

> > to work on the cooling.