[AMRadio] Classic Link Coupled Tuner


james.liles james.liles at comcast.net
Mon Aug 17 10:39:22 EDT 2009


Hi John:
Love the story John --- an inquiring mind is a treasure.  Kindest regards 
Jim K9AXN


----- Original Message ----- 
From: "John Coleman" <jc at pctechref.com>
To: "Discussion of AM Radio in the Amateur Service" 
<amradio at mailman.qth.net>
Sent: Monday, August 17, 2009 8:52 AM
Subject: Re: [AMRadio] Classic Link Coupled Tuner


> 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 sensit
> ivity 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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