[TowerTalk] 30/40/80 DIPOLE (balun/strain relief ideas needed)

[Al Williams]

A dissenting note-- I much prefer my knob-switched MFJ948 to my roller tuned
MFJ969.  The reason is that I change bands, frequencies, and wire antennas a
lot during a contest and the roller inductor is difficult and time-consuming
to crank
to predetermined points, whereas the knob-switched cant be simpler.
Further,
initially finding the match settings requires rocking the roller inductor a
lot

If I want (which I dont) to reduce the VSWR from say 1.3 to 1.1, then the
roller
inductor is more capable.

It would be helpful if manufacturers would calibrate there dials on tuners
such that
increasing the number readout corresponds to an increase in inductance and
capacitance.  Maybe  mfr's other than MFJ do!

k7puc


-----Original Message-----
From: Bill Coleman AA4LR <aa4lr@radio.org>
To: Mark . <n1lo@hotmail.com>; towertalk@contesting.com
<towertalk@contesting.com>; psoper@pjs.East.Sun.COM
<psoper@pjs.East.Sun.COM>
Date: Thursday, June 22, 2000 7:45 AM
Subject: Re: [TowerTalk] 30/40/80 DIPOLE (balun/strain relief ideas needed)


>
>On 6/22/00 10:04 AM, Mark . at n1lo@hotmail.com wrote:
>
>>Your absolute best bang for the buck is an 80 meter doublet (homebrew) ,
>>strung up in a flat-top configuration, and fed with parallel wire
feedline,
>>such as 300 ohm tv twinlead (very cheap and light) or 450 ohm 'ladder
line'
>>(much stronger and durable). This requires either:
>>1) A tuner in the shack having open wire outputs, or
>>2) A remote 4:1 balun, located at the entrance to the shack, such as the
>>Radio Works "remote balun", a coax jumper, and a tuner with coaxial
output.
>
>I generally agree here. And would add a few points:
>
>* Mount the doublet has high as you can. The higher the better. 50-150
>feet if you can.
>
>* Don't use TV twinlead. Use manufactured line with windowed slots (450
>ohm), or make open wire line yourself. Look up my Open Wire Spacers
>summaries in the May 2000 archives of TowerTalk. (See
><http://www.contesting.com>) TV twinlead has a lot of loss.
>
>* For the coax jumper with the remote balun, use RG-8 or RG-213 solid
>dielectric coax. Keep it as short as possible. Since this coax carries a
>complex impedance, high voltage points may appear on it, so using the
>larger, solid dielectric coax prevents potential arcing.
>
>* Overbuild your remote balun. Since it has to handle complex impedances,
>there's little difference of 1:1 or 4:1 or other transformations. Use a 1
>kW balun for a 100 watt transmitter.
>
>* Use a good tuner. Roller-inductor tuners are more expensive, but much
>easier to get a good match.
>
>
>Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr@radio.org
>Quote: "Boot, you transistorized tormentor! Boot!"
>            -- Archibald Asparagus, VeggieTales
>
>
>--
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>
>


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