[TenTec] SLIGHTLY OT

[Art Trampler]

Thanks Jerry.
 
Interesting that there is perhaps some mythology then about the benefit of "true ladder line." this is about 4.5" or 5" spacing, with machined spacers made my a ham-owned machine shop.
 
I'll not rush into changing the feed line, as it took a little while to make it in the first place!
 
Art

--- On Fri, 4/8/11, Dr. Gerald N. Johnson <geraldj at weather.net> wrote:


From: Dr. Gerald N. Johnson <geraldj at weather.net>
Subject: Re: [TenTec] SLIGHTLY OT
To: tentec at contesting.com
Date: Friday, April 8, 2011, 1:29 PM


A quarter wave center fed wire has low radiation resistance and is very 
capacitive. Bad phase angle. You run that through a 600 ohm line about a 
quarter wave long, converts low R to high R and C to L. So your balun 
sees high impedance that may be causing core saturation (for sure in a 
voltage balun) and you see high Z at the tuner.

More wire at the antenna will shift the results, a quarter wave more 
feed line would shift the results, but the easiest change is to lower 
the characteristic impedance of the feeder by going to fatter wires or 
closer spacing. I take you are using 6" spacers. For 300 ohms you need 
only 1/2" spacers. A quarter wave of 600 ohm transforms a 20 ohm load to 
18,000 ohms. A quarter wave of 300 ohm transforms that 20 ohm load to 
4500 ohms which is somewhat easier to match. That 110 feet of feed line 
is close to a half wave or multiple of a half wave on higher bands, so 
the characteristic impedance has much less effect on the impedance seen 
at the tuner.

73, Jerry, K0CQ

On 4/8/2011 12:13 PM, Art Trampler wrote:
> It's on-topic, as I am using a 238B...
>
>
> New antenna, 140' sloping dipole...apex about 50 to 55 feet, ends about 30 feet, so not quite an inverted vee,
>
> Feedline: 600 ohm (or thereabouts) 14 gauge stranded, insulated wire using 73CNC spreaders, Guesstimated length: 110 feet. Feedline and antenna are continuous pieces.
>
> Tuner: 238B, followed by 10 feet of LMR600 to a 1:1 current balun from Balun Designs (to get out of the shack).
>
> On 160 meters, I wound up in Hi-Z "5" position to get a 1.8:1 match. Am I looking at Hi-Z because the antenna length is about 1/4 wave? If so, would it help so add 20 feet to each end, even if it went at nearly a right angle to the antenna? Or is this really unimportant/not an issue as long as I get a match?
>
> Also, what recommendations do other owners have for additional capacitance if necessary? I have not replaced the internal capacitors with the Russian doorknobs but might at some point.
>
> Interested in your thoughts. If the Pegasus S-Meter is at all accurate, I was hearing Russians a full S-unit better on 20 meters last night with this antenna than with my AV640 vertical. Japan is off the end, so the vertical is better in that direction.
>
> 73,
> Art
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