[ARC5] "Curing Chirp in Command Transmitters"

[WA5CAB--- via ARC5]

My thoughts are that the filament voltage in a BC-459 is 24-28 VDC. As his 
isn't, there is no telling what other probably unnecessary mods had been 
done to the transmitter. As has been demonstrated numerous times, Command Sets 
(and many other military sets) work quite well in the unmodified state when 
operated as designed. The H&K is worthless as he gives no information about 
what else had been done to the transmitter to screw it up. Ignore it.

Robert D.

In a message dated 10/4/2014 6:38:13 PM Central Daylight Time, 
r390a.urr at gmail.com writes: 
> 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
> 


Robert & Susan Downs - Houston
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MVPA 9480