Thanks for all your help guys. I think you've hit the nail on the
head. Now it is time for me to do some more reading, and fix this
puppy.

J

I have not seen much description on the solid state amp except that it has
MRF455 transistors. Because these devices were a favorite in the manufacture
of CB amplifiers, I am suspicious that the only output filtering is a HPF
set to cutoff around 30MHz.
So, running this amp on the lower HF bands would allow a lot of harmonic
energy to appear at the output.

Dale W4OP

RADIO-----2 TRANSISTOR AMP-----SWR METER------ ANTENNA

Ok, when I check the SWR on my antenna it shows 1.1. When I turn the
amp on it shows over 3.x SWR. The antenna is rated at 5 KW. The amp
only puts out about 100 watts.

When I had this it was caused by arcing at the antenna. VSWR perfect with
low power, but it even made an audible noise when you screwed the power up.

1 - Try this using a band-pass filter:
RADIO--2 TRANSISTOR AMP--SWR METER--FILTER--DUMMY
If amp churns out **** then the filter will reflect it. If VSWR is good,
then:

2 - Eliminate your feeder (could be breaking down):
RADIO--2 TRANSISTOR AMP--SWR METER--FEEDER--DUMMY
When you do this you may even see a duff contact/joint.
If the feeder insulation is breaking down then VSWR rises again. If not
then:

3 - Check out the antenna / balun / feed points for strands of wire, smoke,
etc.

To think in terms of SWR readings is a waste of time and effort.

You are all confusing yourselves. Furiously digging yourselves even
further into the mire.

Go back to square one and begin again from Ohm's Law.
----
Reg

"Roy Lewallen" wrote in message
...
Joeseph wrote:
, , ,
Assuming you are correct my next problem will stopping the extra
frequencies from getting out of the amp in the first place.

No, your problem should be figuring out how to prevent them from getting
generated in the first place. If the harmonic or spurious content is that
high, there's something seriously wrong.

Nice answer, Roy. That was my knee-jerk, too.

Joseph, remember, the problem isn't only "stopping them from getting out of
the amp...". Those other frequencies are some sort of parasitic in the
amplifier. Besides being stuff you don't want going to the antenna, they
are robbing your amp of the ability to amplify the frequencies you DO want
amplified, and they are unnecessarily heating up your transistors and
sapping their life.

So first, keep them from being generated, then stiffen up that low pass
filter so anything that does get created is way, way down. Far lower than
what will show up as an apparent SWR problem.

...

On Fri, 15 Jul 2005 19:12:06 +0000 (UTC), "Reg Edwards"
wrote:

To think in terms of SWR readings is a waste of time and effort.

You are all confusing yourselves. Furiously digging yourselves even
further into the mire.

Go back to square one and begin again from Ohm's Law.
----
Reg


Actually they are correct. I ran an experiment using a Barker and
Williamson low pass filter with a 32 MHz cutoff.

With the set-up below the SWR went high when the amp was turned on.

RADIO===AMP===SWR METER====ANTENNA

With the set-up below the SWR stayed at 1.1:1 with and without the amp
on.

RADIO===AMP===LOW PASS FILTER===SWR METER===ANTENNA

Also the output of the amp showed about 110 watts without the low pass
filter, but with the low pass filter the watt meter installed after
the low pass filter showed about 75 watts. That means about 30 watts
was being transmitted above 30 MHz even through the fundamental was at
28 MHz.

I doubled the value of the capacitors going form the collector to
ground, and the SWR dropped to 1.5:1 with the amp on and 1.1:1 with
the amp off. Then I add 470 pf capacitors from the trasnsitor base to
ground and the SWR with the amp dropped to 1.3:1 with the amp on.
With the TVI filter in-line the SWR is 1.1:1 with and without the amp
on.

A lack of working space inside the amp case made it difficult to
install a pi-network on the input and output side of the transistor
finals.

Thanks for everyone's help. The SWR increased was caused by harmonics
above the fundamental frequency, and they were outside the bandwidth
of the antenna.

Thanks for sharing your results with the rest of us. That's a good
experiment you described. The only "final clincher" would be if you had a
receiver that covered the spectrum where you might find out what the
spurious signal was that was being generated. Most power transistor
circuits I've seen have all kinds of weird bypassing, ferrite beads on
power-carrying lines, funny adjustable variable capacitors in funny places
in the circuit. Good luck otherwise.

===== no change to below, included for reference and context =====

On Mon, 25 Jul 2005, Joeseph wrote:

On Fri, 15 Jul 2005 19:12:06 +0000 (UTC), "Reg Edwards"
wrote:

To think in terms of SWR readings is a waste of time and effort.

You are all confusing yourselves. Furiously digging yourselves even
further into the mire.

Go back to square one and begin again from Ohm's Law.
----
Reg


Actually they are correct. I ran an experiment using a Barker and
Williamson low pass filter with a 32 MHz cutoff.

With the set-up below the SWR went high when the amp was turned on.

RADIO===AMP===SWR METER====ANTENNA

With the set-up below the SWR stayed at 1.1:1 with and without the amp
on.

RADIO===AMP===LOW PASS FILTER===SWR METER===ANTENNA

Also the output of the amp showed about 110 watts without the low pass
filter, but with the low pass filter the watt meter installed after
the low pass filter showed about 75 watts. That means about 30 watts
was being transmitted above 30 MHz even through the fundamental was at
28 MHz.

I doubled the value of the capacitors going form the collector to
ground, and the SWR dropped to 1.5:1 with the amp on and 1.1:1 with
the amp off. Then I add 470 pf capacitors from the trasnsitor base to
ground and the SWR with the amp dropped to 1.3:1 with the amp on.
With the TVI filter in-line the SWR is 1.1:1 with and without the amp
on.

A lack of working space inside the amp case made it difficult to
install a pi-network on the input and output side of the transistor
finals.

Thanks for everyone's help. The SWR increased was caused by harmonics
above the fundamental frequency, and they were outside the bandwidth
of the antenna.