On Thu, 14 Jul 2005 10:31:05 -0400, Joeseph
wrote:


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

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

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

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.