The reason CBers are trimming their coax is to try and provide a
better load for the transmitter when there is a mismatched antenna.

The feed line in this case acts as an impedance transformer. You know
about them don't you Larry? You remember, a quarter wave line will
transform a short to a high impedance, a half wave line will transform
a given impedance on one end to the same impedance on the other end
regardless what the impedance of the cable is.

Some times trimming the length of the cable can make the feed point at
the transmitter closer to 50 ohms than it was. But the SWR on the
cable will always be the same regardless of the length. That is
determined by the match between the cable and the antenna.

Regards
Gary


On Fri, 21 Nov 2003 03:52:31 GMT, (Larry W4CSC) wrote:

On Thu, 20 Nov 2003 19:08:37 -0500, "Doug Dotson"
wrote:

Wouldn't phase be a problem? Hard to believe that a signal can
be reflected back from the antenna and then reflected back from the
transmitter to the antenna and will be in phase well enough to actually
do any good.

Doug, k3qt
s/v Callista

Isn't that why these CBers are trimming the length of the
coax?.....(c;


Larry W4CSC

NNNN

I feel like the Aflack duck running out of Yogi Berra's barber shop
shaking his head....(c;

Larry W4CSC

NNNN

Agreed!

"Larry W4CSC" wrote in message
...
I feel like the Aflack duck running out of Yogi Berra's barber shop
shaking his head....(c;

Larry W4CSC

NNNN

Next time Lionheart goes to sea, I'm gonna just hook the M802 to the
frame of the porthole above it. SWR will be 50:1. Listen out for me!
Should be 40 over S9, worldwide, with that much SWR reflecting back
and forth!

Wanna buy our useless tuner? We won't need it any more.....

(cue Aflack duck shaking head and running for the hills)

On Mon, 24 Nov 2003 18:23:57 -0500, "Doug Dotson"
wrote:

Agreed!

"Larry W4CSC" wrote in message
...
I feel like the Aflack duck running out of Yogi Berra's barber shop
shaking his head....(c;

Larry W4CSC

NNNN




Larry W4CSC

NNNN

Geeze, read the book Larry. Don't take my word for it.

I even quoted you chapter and verse from the ARRL Bible and the Bird
watt meter manual.

Unless you don't understand what it says, then that's another matter.

This stuff ain't that complicated once you put the old wives tales on
the shelf.

Do the experiment with the tuner and the two watt meters. Then tell me
how much reflected power is going back to your transmitter.

Regards
Gary


On Tue, 25 Nov 2003 00:10:44 GMT, (Larry W4CSC) wrote:

Next time Lionheart goes to sea, I'm gonna just hook the M802 to the
frame of the porthole above it. SWR will be 50:1. Listen out for me!
Should be 40 over S9, worldwide, with that much SWR reflecting back
and forth!

Wanna buy our useless tuner? We won't need it any more.....

(cue Aflack duck shaking head and running for the hills)

On Mon, 24 Nov 2003 18:23:57 -0500, "Doug Dotson"
wrote:

Agreed!

"Larry W4CSC" wrote in message
...
I feel like the Aflack duck running out of Yogi Berra's barber shop
shaking his head....(c;

Larry W4CSC

NNNN




Larry W4CSC

NNNN

Back when we used tubes I remember that the plates would glow red
then white hot depending on a few factors one of which was how the
output pi filter was tuned, For them that don't remember the output pi
filter tuned the output of the plate circuits (usually about 50k) to
the 50 ohms that the coax liked, hopefully the antenna was 50 ohms
also. So the finals were affected a lot by the swr they saw and we
could see it also just by the color of the glow, white meant better
shutdown and retune or just retune without shutting done.






How do you know that you have a better signal when you tune your
antenna for lowest SWR?

An SWR meter is good for telling you when your transmitter is seeing a
flat 50 ohm load. It is useful as a tuning device. Not much more.

Solid state finals don't like complex impedance's. It causes them to
draw excessive currents. High SWR goes along with reflected complex
impedance's. Also the output circuit is usually fixed at 50 ohms. If
you don't match that you will not get maximum power transfer from the
transmitter.

Your solid state transmitter usually has a power reduction circuit
that reduces power out when it sees a high SWR. So having the proper
match at the transmitter will ensure full power out.

On tube transmitters you will usually not find any high SWR protection
circuits. Tubes are very tolerant on complex impedance loads.

As explained in the ARRL HANDBOOK, reflected power does not reach the
finals in your transmitter. See below again.

Regards
Gary

On 24 Nov 2003 18:09:12 -0800, (Gw) wrote:

Back when we used tubes I remember that the plates would glow red
then white hot depending on a few factors one of which was how the
output pi filter was tuned, For them that don't remember the output pi
filter tuned the output of the plate circuits (usually about 50k) to
the 50 ohms that the coax liked, hopefully the antenna was 50 ohms
also. So the finals were affected a lot by the swr they saw and we
could see it also just by the color of the glow, white meant better
shutdown and retune or just retune without shutting done.


You should hear the effect of SWR on a 4-cavity UHF TV transmitter
klystron running 20KV at 5A of collector current.....Most
exciting...(c;

Of course, it's not as near as exciting if the FOCUS magnet or its
power supply have a problem...and the stray electron beam eats a hole
in the side of the 7' tube.

Makes one want to get more involved in high energy physics......(c;

POWER is our FRIEND....




Larry W4CSC

NNNN