----- Original Message -----
From: "Scott Neader KA9FOX" <ka9fox@qth.com>
>I have a 160m inverted vee fed with 75 ohm CATV. Minimum SWR is 1.9:1
> which isn't too far from expected given the 75 ohm cable. I've decided to
> just use a tuner for now, to get me QRV on top band (for the first time in
> my life). I will maybe improve this situation later by feeding the vee
> with 50 ohm cable or explore transformers or other solutions.
>
> Unfortunately, with only about 1kw, my Dentron "Super Super Tuner" starts
> to arc at times. Any recommendations for a tuner that can handle 1.5kw on
> 160m, given my relatively high SWR? Please no home brew projects, as I am
> a QCAO.
>
> Thanks in advance!
>
> - Scott KA9FOX
Hi Scott,
I have a Super-Super Tuner here which I use frequently on 160
meters. It will handle > 1.3 KW (the output of my Drake L-7)
depending on the load impedance. Take the cover off and note
the dial positions corresponding to maximum and minimum
capacitance on the variable capacitors (I use paper overlays
on the front panel to mark tuning presets and the capacitors
min/max positions). When you tune-up the Super-Super
Tuner try using a different tapped inductor setting (I have always
had less arcing using with the next to highest L value instead of the
highest L value). You are looking for a tuning solution that maximizes
the variable capacitor values (maximum capacitance corresponds
to minimum RF voltage across the plates of two series variable
capacitors). If that doesn't work, try adding some 50 ohm coax
between the tuner and the hardline. This will move the phase of the
load impedance which may result in more favorable tuner
settings (you may have to experiment with the length). Assuming
there is nothing wrong with the tuner, the arcing is occuring because
one of the two variable capacitors is set at or near its minimum
capacitance value.
BTW, if you are using a tube amplifier with a PI-network, you
should be able to absorb a 1.9:1 mismatch by adjusting the
amplifier tuning a little and just skip the tuner completely. And
finally, if you decide you must use a tuner and you can't get
the Dentron to work, try the Ameritron ATR-30. I recently
picked up one on the used market. I really like it.
Have fun!
Mike, W4EF..............................................................
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|