----- Original Message -----
From: "Jim Thomson" <jim.thom@telus.net>
To: <amps@contesting.com>
Sent: Saturday, May 05, 2012 9:12 AM
Subject: [Amps] Antenna tuner loss
> Date: Fri, 4 May 2012 09:22:54 -0400
> From: "Carl" <km1h@jeremy.mv.com>
> Subject: Re: [Amps] Antenna tuner loss
>
>
> Tuners with 250pf max on 160 will always be inefficient, a High C tuner with
> 500pf will be very efficient and require proportionally less L. The higher Q
> results in less bandwidth so there is no free lunch.
>
> Its so much easier to modify an amp to be able to do the matching and toss
> the tuner in the dumpster.
>
> Those with autotune amps are left swinging in the wind and need autotune
> tuners (-;
>
> Carl
> KM1H
>
> ## Im afraid you have the the T network info backwards Carl. On
> a T network Tuner, with high C and low L, you end up with LOW
> Q ! The T network is 100% opposite a PI net. With any PI net,
> High C1 + C2 and low L = high Q. On a PI net, low C1 + C2
> and high L = low Q.
>
> ## A T net with low C1 and C2 and high L = high Q. That’s why
> the damn coils in the tuners all burn up in the 1st place. The T net
> in 99% of cases is a hi pass filter.... but who really cares. Any harmonic
> redux should have been done at the output of the amp anyway.
>
> ## Look at Alphas latest T tuner creation. It uses a pair of 7.5 kv
> vac caps + huge edge wound roller coil. They rate it at 4 kw... but
> that’s only for high Z loads. For real low Z loads like say 8-12 ohms,
> its only good for 600W CCS ! With low Z loads, the current is sky high
> through the coil, which limits the PO the tuner can handle.
>
> ## For real low Z loads, the best answer with a T tuner is to just pad
> one or both caps, and use less L. Then you have a low Q network=
> less current through the coils.
>
> ## I agree though, just fix the ant in the 1st place. At a friends place, we
> used a motor driven ceramic vac cap on his 160m vertical. The vert
> is 100 ft tall, with T loading at the top. Its then aprx .375 wave long...
> and R = 50 ohms. The XL is simply tuned out by an equal amount of
> XC provided by the vac cap. SWR is dead flat from 1800-2000
> We stuffed +73 dbm into it, and it doesn’t break a sweat.
>
> ## On my 40M yagi DE, I installed one tiny coil, made from .375 inch
> OD CU tubing into each leg, right at the feedpoint in a box.
> Each coil is shorted out with its own ceramic vac relay. Coils are in the
> circuit on CW... and shorted out on SSB. Real low swr from
> 7000-7300. And no, it cant be blown up with YC-156 power levels.
>
> ## On my 80m rotary dipole, I use a pair of motor driven, compressible
> tubing coils, made from .25 inch OD plastic coated CU tubing. Comes
> with 10 x pre-sets, plus full manual tuning + digital readout. Flat swr
> from 3200-4100 khz. You cant blow this one up either.
>
> ## 20-17-15-12-10m yagis are a non issue for swr these days, so
> no mods done to them, except for bigger OD AL tubing used for the
> hairpins. On the OWA designs, no hairpin is used.
>
> later... Jim VE7RF
It would be easier to refer you to
http://www.arrl.org/files/file/Technology/tis/info/pdf/9501046.pdf
Or you could go to JI's site where he copied a lot of it (-;
MFJ also has a High C tuner which reportedly works very well
There was also a QST review in the 80's or 90's which included a high C tuner
by a small manufacturer that did very well.
Carl
KM1H
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