[Elecraft] Re: SSB Audio Problems

[Paul Wilton]

Confession time - the raspy noise did turn out to be a AC magnetic field 
problem.  I have a 2 foot long fluorescent tube above my desk, about 4 
foot away from my K2.  That is what was causing the raspy audio.

That leaves just one question- when a constant signal is injected into 
the audio input in SSB mode, surely the output should also be a constant 
level RF carrier.  What I when looking at the RF with a scope, the peak 
level jumps around by about 10-20% of the average peak level with a 
random jump a few times a second.  On CW the level is rock solid.  Is 
this expected or am I worrying about nothing in particular?   It was 
this behaviour that made me look at pin 6 of U2 on the SSB board since 
this also seems to jump around once it has slowly reached its final value.

73

Paul
M1CNK

Paul Wilton wrote:

> Thanks for all the advice received so far from everyone on the list.
>
> A couple of clarifications
> a)   I do not believe I have an A-C field problem.  I will double 
> check everything but I didn't have anything within close range.
>
> b)  I don't also believe I have an RF induced problem since I am using 
> a well shielded dummy load
>
> c)  Re the power control, the behaviour I am seeing is occurring AFTER 
> I hit the PTT.  The output of pin 6, U2 (PWR CTRL) on the SSB board 
> seems to drift upwards from 1 to 5 volts pretty slowly.  However, if I 
> turn the power control down, it drops very quickly.  Perhaps this is 
> the intended behaviour.
>
> d)  Annoyingly the raspy CW seems to be intermittent - it has now has 
> stop misbehaving now that I have time to look at it.  I intend to 
> listen to the BFO/VFO on another receiver next time it happens.
>
> Thanks again for all the advice.
>
> Paul
> M1CNK
>
> Message: 19
> Date: Sat, 12 Nov 2005 12:59:58 -0800
> From: "Ron D'Eau Claire" <rondec at easystreet.com>
> Subject: RE: [Elecraft] Problems with SSB Audio
> To: "'Elecraft Discussion List'" <elecraft at mailman.qth.net>
> Message-ID: <000101c5e7cc$0addcd60$c5ddfea9 at RONPORTABLE>
> Content-Type: text/plain;    charset="us-ascii"
>
> "Raspy" is often the description given a signal from a K2 that is sitting
> too close to a transformer so the a-c magnetic field modulates the 
> VCO. If
> you have a power supply, desk lamp with a transformer built in, or any 
> other
> transformer operated device nearby, try turning it off and see if your
> signal clears up.
> If so, there's a mod for the K2 that will dramatically improve its
> resistance to magnetic field effects. See www.elecraft.com for details.
>
> About the power control, are you expecting it to go to work before your
> transmit? It won't! The power control sets the "requested" output. The
> actual output doesn't change until you transmit again, and transmit long
> enough for the power monitor to note the actual output and adjust the
> circuit to match the "requested" level you set with the POWER control. 
> It's
> not uncommon for ops to turn on a rig and notice that even though it's 
> been
> in receive for half an hour, when the hit the key the power stays at zero
> for the first dash or several dits, depending upon the keying speed. 
> That's
> because the power control circuits are only then getting some RF to work
> with to set the actual power output correctly.
> Ron AC7AC
>
>
>