From: "James Cowburn" <james.cowburn@virgin.net>
To: <rsgb_lf_group@blacksheep.org>
References: <017801ca66fb$0bf91c60$0517aac0@jimdesk> <CDD52DF1F4BE4A6197305E939E2F7572@JimPC> <20091118085815.7282031E703@smtps01.kuleuven.be>
Date: Wed, 18 Nov 2009 09:33:45 -0000
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Subject: RE: LF: Re: G7NKS sidebands
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Hi Rik

That's exactly what mine are.  I think it's a mixture of stretching the Pa
on the IC735 so its at the edge of its envelope (the radio equivalent of a
stick shaker or stall horn on a plane!) and also RF leakage and mains
leakage into the soundcard system on the Dell lappy.  It's only apparent on
Rx and Tx of strong/local signals where the fundamental is so high (>0db)
that the first side lobes at -30dB are still within WSPR capture range.

It's mainly an issue with reports from M0FMT (his fault for living so close
to me...hi hi ) and from M0BMU (his fault for having such a good 500 set up
and helping me to get on the band in the first case!  Just joking Jim)

I can cure it by winding back the power a chunk but then I am limiting
myself Dx wise.

Last night I received my first transatlantic stations W1xxx and AA1A.  I
think my antenna mods and good condx really helped.

My next challenge is to get >1000km and then T/A as well as doing some more
CW QSO's.   I will try and get a QSO with Mal perhaps

Actually my first challenge is to keep my antennas up in the 30kt wind that
is blowing around here today!!


With best regards
 
 
Jim G7NKS
 
 
Dr. James Cowburn
E james.cowburn@virgin.net
 

 

-----Original Message-----
From: owner-rsgb_lf_group@blacksheep.org
[mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of Rik Strobbe
Sent: 18 November 2009 08:58
To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: Re: G7NKS sidebands

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" <james.cowburn@virgin.net>
>To: <rsgb_lf_group@blacksheep.org>
>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.