[ARC5] BC-459 Frequency Jump

[Mark K3MSB]

Hi Dick

For antenna matching,  I'm using the UNUN you so generously supplied in
series with a modified HT-37 air variable tuning capacitor.

All the caps in the transmitter were replaced.

Mark K3MSB

On Sat, Jan 2, 2016 at 3:33 PM, David Stinson <arc5 at ix.netcom.com> wrote:

> There are a many things that can cause this.
> This is an MOPA transmitter; in addition to power
> supply issues, anything which changes the loading
> on either stage can cause the problem.
>
> What I hear in the .mp3 files is a drift, not a "jump."
> Jumps are usually caused by, as others have pointed-out,
> intermittent connections, dirty output tuning parts, corroded grounds etc.
>
> While leaky bypass caps and gassy 1625s have
> exhibited this kind of drift, it sounds thermal and I'm very accquanted
> with that issue.  How are you tuning the output to match an antenna?
> If using an external cap and that cap isn't well RF rated, it will heat
> up, change value and that will pull the MO frequency as the loading on the
> PA changes.  You don't see it during a QSO because
> the part heats and cools as you key, averaging the change.   If you had an
> "instant reading" audio freq counter,  you'd likely see
> the changes our ears "average out."
>
> One can spend as much money as one wants on good RF caps.  Seen them for
> $75 and for $5.
> I've found the ones from Eastern Europe
> and Russia to be excellent and cheap.  I use these in series with the
> antenna lead for 80 Mtrs with good results:
> http://www.ebay.com/itm/271738088165
> It will also work on 40 meters but 50 pF is better.
> For 40 meters, I like to use some little green doorknobs from Bulgaria.  I
> don't see them listed right now but they show-up fairly often.  I've had no
> thermal drift issues with these caps.
> 73 DE Dave AB5S
>
>
>
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