[Antennas] Buried ladder line?

2003年10月13日 22:32:07 -0700

The ideas that I have been tossing around as big capacitors of the same size are 
difficult to find and roller inductors have oxidation problems and link couplings is 
almost dead was:
build that trombone capacitor say 2 and then a variable inductor like that used on 
the screwdriver antennas, say 2 also. Then have the wires come to a central point 
where pug jumper or what could connect them in the correct mode for the antenna.
Just how do you build those things though for a person with 6 left thumbs on his 
right hand.
Chris opr VE7HCB
To: 	[email protected]
From: 	Dan Richardson <[email protected]>
Subject: 	Re: [Antennas] Buried ladder line?
Date sent: 	2003年10月13日 20:45:15 -0700
> At 07:05 PM 10/13/2003, you Bob Lay wrote:
> >[snip]
> >
> >Meanwhile, if you have the determination for it, the best plan for a
> >balanced tuner is the one by Dick Measures, published in the Feb 1990
> >QST. I have personally seen one built exactly to those plans. The
> >owner/builder was kind enough to let me examine it and operate it. It
> >is probably even better and more versatile than the Johnson Matchbox.
>> I have both and use both. Dick Measures design, built properly. will
> tune a much wider impedance (differential) range than the Matchbox,
> however, it does not handle high common mode conditions as well as the
> Johnson Matchbox. If your antenna and transmission line are well
> balanced it will work very well. But for antenna systems that are not
> well balanced - such as an off center fed dipole - Measure's tuner
> wouldn't necessarily work much better addressing the common mode
> problem than a conventional T type tuner with a balun. In other words
> Measure's design removes differential impedance stress from the balun,
> but falls remove the common mode impedance stress. (Common mode
> current's path is to ground and that path, in Measure's design, is
> through the balun)
>> I feel Measure's design is a step up from the T-tuner/balun combo
> (particularly for the QRO operator), but the link-type tuner, similar
> to the Johnson Matchbox design, is still the best for matching
> balanced transmission lines.
>>> >Meanwhile, I am hoping to find one of the smaller Johnson Matchboxes
> >that was designed for about 300 watts (AM service) - they are said to
> >be able to handle 1500 watts p.e.p. with no trouble.
>> The small tuner is said to have better efficiency
>>> >To build the Dick Measures design you will need one big variable cap
> >and two identical rotary inductors whose shafts will be ganged
> >together with a toothed belt and driven by a front panel crank with
> >counter. It's a serious project. You may want to look at some of the
> >other designs, as well, that have appeared in the ARRL Antenna Book.
>> What out for the big capacitor as it will also have a big minimum
> capacitance that can be a killer on 10-meters. I had better luck using
> a smaller capacitor and switching in addition parallel capacitors as
> needed for the lower frequencies.
>> Yes, you are quite right it does take some time to find parts and
> build.
>> 73,
> Danny, K6MHE
>>>> - - - 
>> Your moderator for this list is:
> Larry Wilson KE1HZ [email protected]
> _______________________________________________
> Antennas mailing list
> [email protected]
> http://mailman.qth.net/mailman/listinfo/antennas