[TenTec] ant

[Rick - NJ0IP / DJ0IP]

With those coil stock you have to be careful.
B&W usually made two versions of coils, with the cheap one using plastic,
which melts when it is hot.
The more expensive ones used some kind of composite, which would take a lot
more heat before melting.

Maybe I'm being unfair, but I will assume the MFJ coils are the cheap
plastic versions.

73
Rick

-----Original Message-----
From: tentec-bounces at contesting.com [mailto:tentec-bounces at contesting.com]
On Behalf Of Dr. Gerald N. Johnson
Sent: Friday, January 14, 2011 11:28 AM
To: tentec at contesting.com
Subject: Re: [TenTec] ant

I do have a small Johnson Matchbox, but it doesn't have the versatility 
needed for my wire antennas, so I've built my own tuners. My big tuner 
(built long before I owned an E. F. Johnson tuner) is overbuilt with a 
huge coil that's too long with a link in the center. I use a fixed link 
with a variable capacitor, probably 300 pf maximum, in series with the 
link. I use a pair of similar capacitors for the output side equipped 
with alligator clips so I can pick turns on the coil and capacitor 
connections either series for low impedance or parallel for high 
impedance. The link and the output coil do the balancing, I don't force 
balance by grounding the center of the output coil, though that often works.

For 21 MHz and up, my tuners have been single band with a dual section 
capacitor that forces balance by grounding the frame of the capacitor. 
Then I tap the feed line to the turns where it matches. And use a 
variable link instead of the series capacitor on a fixed link.

These tuner circuits are discussed in my 2002 ARRL Handbook long about 
figure 19-10. Construction is illustrated in the 17th ARRL Antenna 
Handbook on page 25-7. For the loads described they all work, some 
better for some loads than others.

MFJ now makes coil stock, that we used to get from B&W. And variable 
capacitors. Mouser carries ceramic wafer rotary switches as does RF 
Parts. RF parts has them in PA sizes for good money. Not cheap.

These circuits have been working for 70 or 80 years.

Sometimes when a tuner doesn't have enough reactance or impedance range, 
we can adjust outside the tuner. Like adding more shunt C or a series 
coil on the LF end, changing the feed line length as much as an eighth 
of a wavelength, or for a very low impedance feed point using a ferrite 
core conventional transformer. These solutions will tend to be specific 
to one antenna on one band.

I'm no fan of tuning a balanced line through a balun. I lost faith in 
that long ago when I tuned up on 10m and didn't hear signals, and when I 
unhooked the antenna the match into the tuner didn't change. I'd 
resonated the balun, not the antenna. A concept that I like better, but 
haven't done it yet is to float the tuner and feed the tuner through a 
balun so the balun always sees 50 ohms or 200 ohms depending on the 
tuner design and without significant reactance. I'm thinking the MFJ 
remote tuner that gets its power through the coax might be good for 
that, but I've not yet tried it.

73, Jerry, K0CQ

On 1/14/2011 8:16 AM, Ed Purvis wrote:
>
> I need the definition and model number of a "good tuner".Hopefully,
something without a balun.  Maybe somethingalong the lines of the K1JJ
homebrew tuner also??
> tnx, Ed
>
> IF AT FIRST YOU DON'T SUCCEED, SKY DIVING'S NOT FOR YOU.
>
>
> --- On Thu, 1/13/11, Dr. Gerald N. Johnson<geraldj at weather.net>  wrote:
>
> From: Dr. Gerald N. Johnson<geraldj at weather.net>
> Subject: Re: [TenTec] ant
> To: tentec at contesting.com
> Date: Thursday, January 13, 2011, 4:41 PM
>
> And 6m and 2m quite well. And probably 160 with a good tuner.
>
> 73, Jerry, K0CQ
>
> On 1/13/2011 3:13 PM, ROD wrote:
>> If you don't work 160 then a good ant. is the double extended zepp  83 ft
on each side for a total 166 ft feed with 450 or 300 ohm ladder line. with a
good tuner you can work 80 40 20 15 12 17 10 meters.  the hams of yester
year use this antenna.   73 Rod Dewald  W3KRQ
>> _______________________________________________
>>
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