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Message-ID: <572081.7375.qm@web28101.mail.ukl.yahoo.com>
Date: Wed, 18 Nov 2009 09:26:48 +0000 (GMT)
From: M0FMT <m0fmt@yahoo.co.uk>
To: rsgb_lf_group@blacksheep.org
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Subject: Re: LF: Re: G7NKS sidebands
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Hi LF
=A0
I think the issue is intermodulation products caused by over driving the=
 the linear RF stages of the TX into distortion=A0because when Jim reduces=
 drive the sidebands petty well disappear at this range. These observation=
 is based upon test carried out yesterday. There is another issue Jim seem=
s to have which is that his PA grossly over heats (I think I am right) whe=
n he reduces drive and that shouldn't happen. For modulation to take place=
 the output=A0of the modulator has to be mixed (hetrodyned) with the RF si=
gnal. In this case I am guessing that the carrier is modulated by noise (5=
0c/s say) in the non linear (over driven linear RF stages) in the TX drive=
r or output.
The fact the PA over heats on reduced drive suggests to me the bias on the=
 PA transistors is being altered by changes to the drive anther indication=
 that the TX output may not be entirely linear

--- On Wed, 18/11/09, James Moritz <james.moritz@btopenworld.com> wrote:


From: James Moritz <james.moritz@btopenworld.com>
Subject: LF: Re: G7NKS sidebands
To: rsgb_lf_group@blacksheep.org
Date: Wednesday, 18 November, 2009, 1:13


Dear Jim LF Group,

Looking at the sidebands on the G7NKS WSPR signals, mains hum or other noi=
se by itself is not a sufficient explanation of what is seen. Simply addin=
g 50Hz, 150Hz, etc. noise into the PC audio channel, then feeding the resu=
lt into an SSB TX would give unwanted CW at frequencies offset from the SS=
B carrier frequency by +/-50Hz, 150Hz and so on, i.e. with the carrier "di=
al 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 signa=
l frequency by +/- 50Hz, 150Hz, with identical modulation to the wanted si=
gnal. This requires some sort of non-linear process to cause the intermodu=
lation 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 descriptio=
n 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 fer=
rite components due to the low operating frequency. But this wouldn't expl=
ain 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 no=
ise 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 PL=
L synthesiser, which would certainly be prone to this type of spurious sig=
nal, since any kind of mains noise getting in would modulate the VCO frequ=
encies, and would probably be the same on transmit and receive. This could=
 be checked by receiving a clean carrier somewhere around 500kHz, and exam=
ining the audio output using Spec Lab or Argo or similar to see if 50Hz an=
d 150Hz sidebands are present on the received audio tone.

Cheers, Jim Moritz
73 de M0BMU


----- Original Message ----- From: "James Cowburn" <james.cowburn@virgin.n=
et>
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
>=20
>=20
>=20
> Sidebands are back!=A0 I think its caused by my TX getting hot and bothe=
red by
> struggling at 500.=A0 From cold it txs 50 watts but this soon drops back=
 to
> around 35, and the sidebands appear.=A0 My sigs are better so having the=
 txfr
> outside the shack and at the antenna is a vast improvement, but I now ne=
ed
> to work on the cooling.





     =20

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<table cellspacing=3D"0" cellpadding=3D"0" border=3D"0" ><tr><td valign=3D=
"top" style=3D"font: inherit;"><DIV id=3Dyiv704142894>
<DIV>Hi LF</DIV>
<DIV>&nbsp;</DIV>
<DIV>I think the issue is intermodulation products caused by over driving=
 the the linear RF stages of the TX into distortion&nbsp;because when Jim=
 reduces drive the sidebands petty well disappear at this range. These obs=
ervation is based upon test carried out yesterday. There is another issue=
 Jim seems to have which is that his PA grossly over heats (I think I am=
 right) when he reduces drive and that shouldn't happen. For modulation to=
 take place the output&nbsp;of the modulator has to be mixed (hetrodyned)=
 with the RF signal. In this case I am guessing that the carrier is modula=
ted by noise (50c/s say) in the non linear (over driven linear RF stages)=
 in the TX driver or output.</DIV>
<DIV>The fact the PA over heats on reduced drive suggests to me the bias=
 on the PA transistors is being altered by changes to the drive anther ind=
ication that the TX output may not be entirely linear<BR><BR>--- On <B>Wed=
, 18/11/09, James Moritz <I>&lt;james.moritz@btopenworld.com&gt;</I></B>=
 wrote:<BR></DIV>
<BLOCKQUOTE style=3D"BORDER-LEFT: rgb(16,16,255) 2px solid; PADDING-LEFT:=
 5px; MARGIN-LEFT: 5px"><BR>From: James Moritz &lt;james.moritz@btopenworl=
d.com&gt;<BR>Subject: LF: Re: G7NKS sidebands<BR>To: rsgb_lf_group@blacksh=
eep.org<BR>Date: Wednesday, 18 November, 2009, 1:13<BR><BR>
<DIV class=3DplainMail>Dear Jim LF Group,<BR><BR>Looking at the sidebands=
 on the G7NKS WSPR signals, mains hum or other noise by itself is not a su=
fficient explanation of what is seen. Simply adding 50Hz, 150Hz, etc. nois=
e 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 502.4=
kHz, 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 +/- 50=
Hz, 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.<BR><B=
R>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 thi=
s frequency, the PA linearity may well be poor due to the impedance matchi=
ng, 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 ge=
ts multiple received signals from a strong station with a clean signal, wh=
ich 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.<BR><BR>A possibility that would explain the unwanted sideban=
ds 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, si=
nce this is just a simple crystal oscillator. I see the IC735 has some sor=
t 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 modula=
te the VCO frequencies, and would probably be the same on transmit and rec=
eive. 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=
.<BR><BR>Cheers, Jim Moritz<BR>73 de M0BMU<BR><BR><BR>----- Original Messa=
ge ----- From: "James Cowburn" &lt;<A href=3D"http://uk.mc281.mail.yahoo.c=
om/mc/compose?to=3Djames.cowburn@virgin.net" rel=3Dnofollow target=3D_blan=
k>james.cowburn@virgin.net</A>&gt;<BR>To: &lt;<A href=3D"http://uk.mc281.m=
ail.yahoo.com/mc/compose?to=3Drsgb_lf_group@blacksheep.org" rel=3Dnofollow=
 target=3D_blank>rsgb_lf_group@blacksheep.org</A>&gt;<BR>Sent: Monday, Nov=
ember 16, 2009 8:26 PM<BR>Subject: LF: rule #2 - assumption is the brother=
 of all foul
 ups<BR><BR><BR>&gt; LF<BR>&gt; <BR>&gt; <BR>&gt; <BR>&gt; Sidebands are=
 back!&nbsp; I think its caused by my TX getting hot and bothered by<BR>&g=
t; struggling at 500.&nbsp; From cold it txs 50 watts but this soon drops=
 back to<BR>&gt; around 35, and the sidebands appear.&nbsp; My sigs are be=
tter so having the txfr<BR>&gt; outside the shack and at the antenna is a=
 vast improvement, but I now need<BR>&gt; to work on the cooling.<BR><BR><=
BR></DIV></BLOCKQUOTE></DIV></td></tr></table><br>



     =20

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