[Antennas] Buried ladder line?

[Les Severson]

Thanks for the comparison data between the Measures design and the 
Johnson M'box Dan...  I had thought of building the Measures tuner but
I think I'll just be happy with my Johnson box..   Incidentally,  I use 
the 300w (AM)  model  which doesn't complain a bit at the output of my
TL-922A amp.    The Johnson box can be found ocassionally on ebay and 
usually run a bit over $100.   A bargain compared to some of the junk on 
the
market nowdays.
I just wish some manufacturer would design and build a good link coupled 
tuner again...  I think there is a resurging  interest in balanced 
feeding antennas for
many reasons.
73,    Les,  W�OJH   

Dan Richardson wrote:

> 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
>
>
>
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