[TowerTalk] FW: In Shack Tuner Vs. Remote Tuner for Multi-Band Antennas

[Jim Lux]

On 5/7/14, 1:34 AM, Chuck Smallhouse wrote:
> This interesting subject has so far has been educational !
>
> But the original subject , I thought, would be discussed about shack
> versus remote antenna tuners, which is a design project that I am
> interested in.
>
> My feeling is that most, if not all, antenna variable compensating units
> (tuners), would be better served by installing them as close as physical
> and mechanical possible to the antenna feed point, They could then
> "Match" the antenna to 50R and allow VSWR free, and almost lossless,
> coax to transport the signals to and from the antenna,  Of course this
> technique/concept works best when used with multi band/frequency antennas,
>
> At present I'm loath to find a QRO or better yet a QRO++, tuner suitable
> for remote weather resistant mounting, other than the MFJ 998RT, and
> it's only single ended.  I'd prefer one that also made the conversion
> from balanced input to 50R output.


I wouldn't worry about the balanced to unbalanced.  Your typical system 
will be Antenna:matching circuit:RF choke on feedline.  The choke solves 
the "unbalanced feedline" issue. You don't really care if the case of 
the electronics is connected to one side of your dipole and the antenna 
terminal is connected to the other side.  It makes your dipole slightly 
asymmetrical, and probably changes the feedpoint impedance a bit, but 
that's what the autotuner is for.

If you were feeding a long boom yagi for EME, and were going to obsess 
about side/back lobes for keeping the system noise temperature down, 
sure, you'd not want that big box munging up the pattern, but I can't 
imagine it having a very big effect on any HF antenna.


SGC's biggest antenna coupler (their term) is 500W, and is probably 
conservative at that.

Given that "power rating" practices of the various manufacturers are not 
consistent, it might well be that MFJ's 1500W tuner is comparable to 
SGC's 500W device.

To a first order, I'd look at physical size, and then look at the 
internal design: how big is the wire on the inductors, what kind of 
capacitors are they using and what's their loss tangent at HF.

If you have an idea of your typical load impedances, then you can use 
one of the matching network loss calculators (W9CF has one on line at 
hhttp://fermi.la.asu.edu/w9cf/tuner/tuner.html)




>
>
> Q.: In keeping with the true subject of this O.T., will this be an
> advantage over, only using the auto tuner in my PW-1 PA ?    And why
> aren't there more remoteable, QRO, WX proof, auto tuners, on the market ?
>

Hams don't buy them.   SGC sells/sold far more autotuners to non-ham 
customers than to hams. Ditto for all the other vendors, except possibly 
MFJ.

Hams like things with knobs they can turn.
Hams like equipment that they can take the lid off of and admire the 
inside components.  That's hard to do when the box is weatherproof and 
at the top of a tower.<grin>