[Amps] placement of RF choke bypass cap.

[David J Windisch]

I wrote the original post on 3/15 because the Ten-Tec Titan 425 is laid out as described.  There is also a 20-ohm 25W wirewound series resistor making up part of the 11-inch lead-length from the cold end of the choke to the bypass capacitors on the back panel adjacent to the HV connector.

Turns out that the choke by itself has a series-resonance near 12M.  If the bypass is moved right up to the cold end of the choke, the suckout can be seen looking in the output connector with, eg, a '259 antenna analyzer.  Set the bandswitch to 10M and tune and load capacitors to min.

Replacing the choke with p/n RFC-3 from rfparts.com, and putting the bypass right at the cold end, made several differences in circuit operation.  The tank setting for max-power-out, Ip-min, and Ig-max on 15M and up coincide, and there is more power out on 12M.  My guess is that the choke and resistor were dissipating significant r-f power.

I'm intending to see if changing to this choke will work in an Alpha 89.  It has a relay kluge, which shorts out turns at the hot end of the choke.

Brgds,
Dave Windisch, N3HE