[AMRadio] Classic Link Coupled Tuner


John Coleman jc at pctechref.com
Mon Aug 17 09:52:36 EDT 2009


Hi Brian:
	Next time we come up there I will be sure to give you some notice.  But I had already taken a side trip to Don's, K4KYV, to get rid of some stuff.  I was needing to spend some time with the kids there in Searcy.  
	If you are getting a good match and there is no heating then the energy from the XMTR must be getting to the antenna.  I would worry too much about it all.  But it sounds like you have the same brain disease that I have, CAN'T STAND TO NOT KNOW WHY.  I must have spent weeks studying and experimenting with this matching stuff and neutralizing circuits, don't even get me started. HIHI  One thing I have found is that the breadboard design is the best for changing and learning and the shot glass can be used for an insulator or to ease the frustration, which comes often for me.
	While on the subject, I must tell you of an experiment I did some time back (25 years ago).  I put a 6AL5 tube in the top box of a Heath Cantenna and lit it up with a 6V lantern battery.  Using only one diode, I connected the plate directly to the dummy load and the cathode was by passed to ground with a .01uf ceramic capacitor and then connected to the little RCA jack on the top box.  Now I had a decent peak reading RF detector.  I just measure the DC on the RCA jack to indicated the peak of the RF voltage (very accurate by the way, but that's another story).  I took 60 ft of open wire  balanced line made of #12 wire with Phenolic spacers about every foot and stretched it out across the back yard suspended by wood chairs and such.  The dummy load RF detector was then attached to the far end.  I had the balanced antenna tuner connected to the feed end and a SWR meter between the tuner and the XMTR.  I adjusted the tuner so that running 800 watts and with the SWR meter sensitivity all the way up it showed nothing on the reflective meter.  I then took my Simpson meter out to the dummy load and measured the voltage at the output of the 6AL5 RF detector.  I of course don't remember the exact voltage but let's say about 250V DC.  Then I connected 100 Ft of RG8 to the dummy load and the other end to the SWR meter.  The SWR meter still show flat but the RF detector meter showed less voltage, not much less but something like 240V.  I thought maybe I have made a slipup somewhere so I when through all the procedures again making sure that I disconnected the battery from the 6AL5 when not measuring so as not to have the filament voltage going down in between measuring.  I got the same results each time.  So I was finally convinced that the losses in a good tuner are negligible and the looses of coax far exceed the losses of open wire line.
 
John, WA5BXO


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