I think the point being missed here by one of the posters is that if the
feedline is really excellent....like the 1/2 inch Heliax, or perhaps 450 ohm
transmitting ladder line, or less radically, perhaps Times Microwave
LMR-400, the losses in the feedline are trivial, no matter the mis-match.
Then having the tuner in the shack is extremely handy, and results, as
indicated, in only trivial losses.
Of course, if one is using 20 year old RG-58, then most of the power will go
away in the feedline, if it doesn't melt first.
So lets be sure we compare apples to oranges.
73 de Gary, AA2IZ
----- Original Message -----
From: "Roger Borowski" <K9RB@bellsouth.net>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Sent: Thursday, January 19, 2006 9:37 AM
Subject: Re: [TenTec] What makes the 238 good or any other tuner good?
> That would be a good name for them, Rob. In essence, the place to use a
> matching network to avoid feedline losses is at the antenna feedpoint.
> Although using an antenna tuner at the transmitter end of the feedline is
> commonplace, it is not the best place to use it, just the most convenient.
> As I indicated in a previous post, if one was to measure the mismatch on
the
> antenna side of the tuner, you can then get an idea of your feedline loss.
> If in your case, your losses are as low as you say, you really don't need
> the tuner as it is just allowing you to apparently tune out a relatively
> minor reactance and feel better in doing so. In cases where the antenna
> tuner in the shack is being used to prevent an SWR foldback of the
> transceiver, allowing it to provide its full rated output power, much of
> that power is being used to warm the coaxial feedline and the matching
> network in the tuner instead of being transferred to the antenna to be
> radiated. 73, Rog-K9RB
>
> ----- Original Message -----
> From: "Rob Atkinson, K5UJ" <k5uj@hotmail.com>
> To: <tentec@contesting.com>
> Sent: Thursday, January 19, 2006 8:27 AM
> Subject: Re: [TenTec] What makes the 238 good or any other tuner good?
>
>
> Hi Roger,
>
> since you seem to proudly eschew the use of a tuner, I'd like to know what
> you call that matching network you have at the f/p of your inverted L--a
> feedpoint reactance remover maybe?
>
> I modelled the loss on my run of 1/2" heliax to my 160 m. inverted L for a
> matching network at the f/p v. if I tuned the line to 50 j0 in the shack.
I
> found that if I put 1 kw into the line in the shack and had the network
> tuning at the feedpoint, I'd gain a whopping 8 watts delivered to the
> antenna (well, actually 5 watts because the LC network I'm building would
> dissipate 3 watts), compared to if i put the network in the shack right
> after the tx. I decided 8 watts out of 1 kw wasn't worth going outside
to
> the feedpoint for every qsy, or constructing a motor drive and control box
> for this thing.
>
> I don't know how many antennas are actually 50 j0 at the feedpoint in a
ham
> band without any coils, stubs, tuners, baluns etc. at the feedoint, but
I'd
> prefer to not limit myself to them and the one or few frequencies where
they
> are 50 j0.
>
> 73,
>
> rob / k5uj
>
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