[TenTec] Re: [TowerTalk] Re: Impact of Reflected Power

Del Seay seay@alaska.net
Thu, 30 Jul 1998 14:37:17 -0800

Okay Guys: No matter what the type of transline, if significant
vswr is present, the resulting nulls and peaks will radiate.
Granted, not much - but, it will distort the radiating pattern
due to in/out of phase addition/subtraction with the radiated
energy from the antenna.
And - no - it will not burn up the amplifier, as the rf returning
from the antenna is reflected back again towards the antenna.
(With or without a "tuner")
Solid state amps are adversely affected due to the inability
to transfer rf to the line and in that instance, damage can be done
to the pa.
Distorted antenna patterns sometimes are a plus, i.e.: contesting.
On the other hand, dx-ers go to great length to shape their
Good or bad is up to the individual!
de KL7HF

-----Original Message-----
From: DavidC <davidc@bit-net.com>
To: Jim Reid <jreid@aloha.net>; tentec@contesting.com
Date: Thursday, July 30, 1998 1:33 PM
Subject: [TenTec] Re: [TowerTalk] Re: Impact of Reflected Power

>Thank you for posting this.  This is the clear and simple explanation of
>all of this I have sought from someone who has considered all of the
>elements of the discussion and who is speaking from the practical
>application world of daily Amateur Radio operation.
>Is this summary correct?
>The TX ships out 100w, it travels out to the antenna (hopefully barring any
>significant mismatches or losses along the way), on occasion an antenna
>mismatch occurs (perhaps at the band edges of the antenna) and some power
>is reflected back where it is resolved before reaching the TX by a manual
>tuner or autotuner which then reflects it back to the antenna.
>The result is that a miniscule amount of the 100w of power is lost in the
>system and the rest is radiated by the antenna in the desired direction.
>And no one at the receiving station is any the wiser that any reflection
>has occured.
>Question:  If I run mostly 75 ohm low loss 3/4 inch CATV cable from my
>shack to my antennas (about 200 feet when all is said and done) but use
>flexible 50 ohm cable at the end points, have I injected loss and
>mismatches that cost me the loss saved by the use of the CATV cable?  Is
>the use of 50-75 ohm baluns then justified?  Is 200 feet not worth the
>hassle of using the CATV?  (It's free!)
>My operation is mostly 160-10m w/occasional 2 and 6m.  SSB, Amtor and
>Pactor.  I will be running 100w most of the time and full legal as
>73, DavidC  AA1FA

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