[Milsurplus] TCS-9 Output matching?

[Roger Basford]

Hi Thomas,

I think the mod I heard about was a link winding over one of the coils 
in the output circuit, so quite like the balun suggested by another 
poster. Using a Windom is a possibility here too, so I may give that a 
try. I'd be interested to know what the military did when they wanted to 
use the TCS with a bigger antenna than the supposedly standard 20ft whip.

The mod to move the RF ammeter to the antenna lead was apparently 
because under certain (unspecified) circumstances the meter in the 
ground lead could show a reading when the in fact little power was going 
out to the antenna. I have a second, junker, TCS TX here and that has 
either had the mod done or was built that way.

I've had an experience, back in the '60s, of seeing a lightning strike 
near a pair of 600 Ohm feeders connected to an RCA ET4332 TX, which had 
an RF ammeter mounted outboard in each feeder leg. The guts of the 
meters exploded and popped out like a pair of eyeballs. Scary stuff if 
you were close to the set at the time!

Thanks for the suggestions,

Roger/G3VKM



On 05/05/2011 20:10, Thomas Adams wrote:
> At 11:33 05-05-11, Roger Basford wrote:
>> Hi All,
>>
>> I'm putting together a TCS-9/TCS-12 station and I read a mention of a
>> simple mod to allow the TX to use coax-fed antennas. Has anyone got a
>> copy of this? I'm getting  about 1.5 amps RF into a BC-375 dummy load
>> but not had much success with an end-fed 66ft inverted L on 80 metres.
>
> */Too low an impedance, obviously.
>
> What worked here on 160 meters was a half wave wire, fed Windom style
> (a single random length wire feeding it 14% off center, driven against
> ground).  Worked beautifully; according to the books, that's about 300
> ohms feed point impedance.
>
>
> /*
>> Also, the handbook I downloaded has an addendum showing a mod to the
>> antenna current meter, moving it from a ground lead to the feed to the
>> antenna terminal, which seems more logical to me. Any thoughts on this?
>> With an external RF ammeter in the feed to the dummy  load I get the
>> same reading as the panel-mounted meter.
>
> */Moving from the antenna terminal to the ground lead SHOULD produce
> an identical reading; all you're doing is rearranging the circuit 
> components
> slightly.
>
> If nothing else...  moving the RF ammeter to the ground lead clearly and
> effectively proves to Newbies that the ground system IS a necessary 
> part of
> an antenna system.
>
> The ground lead arrangement DOES have a slight advantage.
>
> In AM broadcasting antenna arrays, RF ammeters are normally jumpered
> with shorting straps when not being used to protect them from destruction
> by a lightning strike on the antenna. While that's not as critical a 
> factor here,
> the addition of a simple switch to short the hot terminal of the meter to
> ground is very easy to do.
>
> Also...  it's my feeling that the readings of an RF ammeter in the 
> ground lead
> are slightly more accurate than those in the antenna lead. In the 
> antenna lead
> configuration, part of the RF to the meter is SHUNTED AROUND it by 
> capacitance
> between the meter movement and the panel it's mounted in!
>
> Again, a broadcasting / higher power analogy... in bigger rigs than 
> the TCS you'll
> frequently see RF ammeters mounted on insulated subpanels. If this 
> isn't done,
> there's danger that the shunted around current can become so large 
> that the
> voltages between the meter movement and a metal panel can build to the 
> point
> where the case of the meter will literally BREAK DOWN and flash to 
> ground!
>
> Just a few rambling thoughts on RF ammeters and their applications.
>
> 73's,
>
> Tom, W9LBB
>
>
> /*