Hi all,
the AM sidebands on my signal were in average 33dB down on the
"real" signal, meaning that the sideband ERP was about
0.1mW.
Having a look at the WSPRnet database showed sideband WSPR spots from
GM4SLV: 1102km with 0.1mW ERP !!!
73, Rik ON7YD
At 10:42 18/11/2009, you wrote:
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.
|
