10 KW CCS ON 6M...USING THE 3CX-6000A7... PART 15 The bypass SWR ended up
being aprx 2.5:1 Various fixed cap value combo's were tried, (including a
temp air variable) wired between the NC contact of one of the RJ2B's..and
chassis. The lowest bypass SWR was 1.8:1 The way the cap to ground trick
works is it amounts to a shunt C and a series L, (XL) is coming from
passing through the big RJ2B)... and transforms the Z down a bit. In most
cases the cap to ground will work on smaller relays, and relays like 3PDT
in a SB-220, when trying to flatten the bypass SWR on 10m, etc. Easier
explained on a smith chart. The XL of the RJ2B's is too high a value for
the cap to ground trick to work. Ok, plan B. 70 pf wired in SERIES with the
NC contact of the RJ2B (then coax from the other end of the 70 pf...to the
hot side of the smaller RG-400..and off to the NC of the smaller RJ1A input
relay. In this config, the 70 pf (44.58 ohms of XC) cancels out the XL of
the RJ2B, etc. The 70 pf consists of a 50 pf HT-58 doorknob (actually
measures 44.5 pf) in parallel with a 25 pf HT-58 doorknob (actually 24.5
pf). Ok, now bypass SWR is down to 1.2:1 With an exact, precise cap value,
the bypass SWR can be reduced to 1:1. Both these caps used are NP0 types,
don't drift, and handle a LOT of current on 50 mhz. They have to be able to
handle 1200 watts on 6M, on bypass mode, since the IPA is an Ameritron
AL-1306 SS amp. The SS amp's don't like high SWR, and the 1306 does not
have a built in auto tuner. So the issue was fixed right at the source. I
believe this is the 1st time a cap has been used in SERIES to cancel out
the relay XL. The drawback is.... the 70 pf ends up being a LOT higher XC
as freq decreases. Like 1263 ohms on 1.8 mhz. Happy Xmas everyone. Jim
VE7RF https://www.youtube.com/watch?v=hI3D_QvmkM8
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