[ARC5] "Curing Chirp in Command Transmitters"

[Ronnie Hull]

I like my chirpy command set tx's!

Sent from Ronnie's IPhone

> On Oct 4, 2014, at 18:38, Dave Merrill <r390a.urr at gmail.com> wrote:
> 
> One of my 'finds' at Shelby last month was a 1947 edition of "Hints and
> Kinks for the Radio Amateur."  In the 20 page "Converting War Surplus"
> section, I found the following:
> 
> <begin quotation>
> 
> Curing Chirp in Command Transmitters
> Alfred Scott Cline, W6LGU
> 
> My BC-459-A chirped and from what I've heard on the air, most everybody
> else's does too.  I tried various methods of keying, and extremes of
> voltage stabilization, but the chirp persisted.
> 
> Checking with a good v.t.v.m. showed 12.6 volts on the filaments with the
> key up, but from 18 to 22 volts when the key was closed!  The added voltage
> was r.f.
> 
> To remedy this situation, shielded filament wire was substituted in the
> rig, with by-passes at each end of the wire.  Old microphone cable (with
> high r.f. losses) seemed best.  A heavy copper strip was run across the
> chassis and the "cold" ends of the 1625 filaments and the cathodes were
> connected to it to get a good ground.  This change resulted in chirpless
> keying for me and has done the same for all the others to whom I have
> passes this hint.
> 
> <end of quotation>
> 
> Okay, I know Command Set keying chirp has been beat to death but perhaps
> this is still worth discussing.
> 
> W6LGU does not mention how he is keying the BC-459-A which might be helpful.
> 
> Even without this information, my suspicion is the unwanted r.f. is coming
> from unshielded filament leads OUTSIDE the transmitter.
> 
> Thoughts?
> 
> 73,
> Dave
> N9ZC
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