[ARC5] TCS 50-Ohm Matching Configurations.

[J Mcvey]

 Why is everyone loathe to use a 4:1 or 9:1 unun autotransformer to match these radios?If your antenna is in the 30 to 90 ohm area, it's a home run every time.These radios were desined for very short antennas and have resistance range of 5 to 12 ohms and can tune against a reactance  of zero up to 800 ohms or so.

The series cap method depends a lot  on the cable length and what impedance is being presented due to that length.The shunt  variable cap on the output will ( hopefully) produce an L section with the internal inductor that will tune the appropriate range.Of coarse, the other variable with any of this stuff is characteristics of your local antenna...

    On Friday, May 11, 2018, 10:59:19 AM EDT, DSP3 <jeepp at comcast.net> wrote:  
 
  
Dave,
 
Very good info.  I tried them out bhut the one that falls into place for me is using Tap 5.  I can't get power out using Tap 4 or 6?  The R-24 Q-5er crapped out yesterday but found a bad cap buried in the rear area, the audio primary bypass was bad.  That's a new one?  Back on the air.  I run about 600v and tuned indicating 165ma for 38 watts output.  Scope looks quite good.  I will archive your data in my ARC-2 manual.  Who knows who will need it in 30 years????
 
Jeep - K3HVG
 
 
 On 5/11/2018 7:50 AM, David Stinson wrote:
  
 Yesterday, I took a few minutes to test three of 
the suggested capacitive matching methods which 
adapt a 50-Ohm non-reactive load to the output 
of TCS and similar transmitters.  The ARC-2 is 
on the bench and it has an output circuit similar
to the TCS, so used that for the test.  
Can get some time to do this on the TCS 
if anyone is interested.  This wattmeter has not
been calibrated in some time, so take these 
Power readings as relative.

ARC-2 Primary 27V. Dynamotor B+ 
All tests at 3890 KC, tuned for max out.

100 pFd capacitor in series to load.
40 W out.
130 mA PA current.
ARC-2 Ant Tuning 472

1000 pFd ANT to ground.
40 W out.
145 mA PA current.
ARC-2 Ant Tuning 652

Capacitive Divider (TCS tuning box)
270 pFd ANT to Load,
1370 pFd, Load to Ground.
44 W out.
190 mA PA Current.
ARC-2 Ant Tuning 576

"Each to their own," of course.
My preference is to trade 10% of power out
for a 30% reduction in PA current, which is
not only easier on the PA, but makes fully
modulating the rig that much easier as well.

GL OM ES 73 DE Dave AB5S




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