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[TowerTalk] Re: [losses]

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Subject: [TowerTalk] Re: [losses]
From: (John Langdon)
Date: Tue, 16 Nov 1999 17:02:35 -0600
If you test the internal automatic antenna tuners in many new transceivers
you will find, even on a relatively small mismatch, that you can get 100W to
the load with no tuner and only 80 or so with the tuner engaged.  The tuner
will get you more output in many cases only when the SWR protection is
cutting the input power back.  A good quality external tuner will have
significantly less loss in many cases.  Those little inductors squeezed into
the case are not as good as full sized ones in a larger enclosure, among
other things.  Dick Weber pointed out in his presentation at the W5 DX BASH
recently that some guys will spend a kilobuck to double their boom length to
get 1.5 dB, when they could get that much improvement with a $300 external
antenna tuner, or some better coax.  And before you flame me, the tuner and
coax improvement will work on receive too, unless reciprocity has been
repealed since I finished school.

Also, the loss inherent in a long coax run will fool you into thinking you
have a better SWR than you do, since the return power is doubly attenuated.
Have you ever measured your SWR on ten meters at the antenna and again at
the shack and compare them.  Many are in for a surprise.

73 John N5CQ

-----Original Message-----
[]On Behalf Of George T. Daughters
Sent: Tuesday, November 16, 1999 4:03 AM
Subject: [TowerTalk] Re: [losses]

In the discussion of line and tuner losses, Ward wrote...

> 30% sounds like a lot, but it's only 1.55 dB.  Not to be ignored, by any
> means, but not a brutal signal reduction.  0.5 dB is about 10% signal
> loss.

It seems we often get fooled by such things.  I remember acquiring a
bunch of old but apparently good RG8 coax.  Before I ran it "up the
tower" I decided to test it at 29MHz.  I put a dummy load on one end,
and my Bird 43 and transceiver on the other end.  I sent 100W down
the line (I couldn't measure any Watts coming back).  Then I moved
the Bird to the dummy load end, and keyed up.  Only 85 watts were
making it down there! "That's a fifteen percent loss!  This stuff is
junk!"  I then checked the manufacturer's specifications... the coax
was in spec. for NEW cable!

Fifteen percent = about 0.7 db loss for however many feet I had.
Gee, 0.7 db doesn't sound like as much as 15%!


George T. Daughters, K6GT

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