Date: Wed, 18 Nov 2009 11:15:36 +0100
To: "rsgb_lf_group@blacksheep.org" <rsgb_lf_group@blacksheep.org>
From: Rik Strobbe <rik.strobbe@fys.kuleuven.be>
In-Reply-To: <02ac01ca6832$39e82890$0517aac0@jimdesk>
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Subject: RE: LF: Re: G7NKS sidebands
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Jim,

I lowered my antenna last night as gales up to 100km/h are predicted.
Regarding CW: let me know when you are ready and I will look out for 
you. I worked G's with only few mW ERP in the past.

73, Rik  ON7YD - OR7T


At 10:33 18/11/2009, you wrote:
>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.