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.

After reading all the other replies up to this moment, let me ask if you:
1. remove the radio (i.e. run the amp without the radio connected at all)
what do you get (if any reading of forward and/or reflected power), and
2. leave the radio connected to the amp, but run the amp without drive
power at all, then what do you get?
3. Can you vary the drive level (say down to lower levels) and still see
the SWR go up.
From what was written below, its not clear for sure if you are implying
that the amp did have a proper level of RF drive or not. But, I'd still be
interested in knowing if you get forward power and/or reflected power with
the amp turned on but without drive. I've actually had amplifiers where
the application of power and certain tuning conditions cause extra
frequencies to come out in addition to what was supposed to come out. And,
sometimes I got self-oscillation if the amplifier was NOT being driven
with input drive.

------------- No change to below, included for reference and context---

On Thu, 14 Jul 2005, Joeseph wrote:

Date: Thu, 14 Jul 2005 10:31:05 -0400
From: Joeseph
Newsgroups: rec.radio.amateur.homebrew, rec.radio.amateur.equipment
Subject: What would cause the SWR to go up drastically when I turn my amp on?




This is a very screwy problem. First lets get the set-up of my
radio equipment;

The amp puts out about 100 watts on HF.

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

Note the SWR meter comes AFTER the 2 transistor amp.

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.

Hmmm.....Ok lets see what happens when I use my 1 KW oil filled dummy
load.


RADIO----- 2 TRANSISTOR AMP----SWR METER-------1 KW DUMMY LOAD

Same thing. The SWR is about 1.5 in to the dummy load, but as soon as
I turn the amp on the SWR meter shows 3.x plus.

Ok, Maybe my SWR meter is screwy, so lets use my Dentron MT3000
tuner with a built in 200 watt dry dummy load and built in SWR meter.


RADIO ----2 TRANSISTOR AMP----DENTRON MT3000

Same thing. The SWR is low without the amp on and goes high when the
amp gets turned on.


Ok, Lets see what happens when I use my Drake L-4B amp instead of the
2 transistor amp.


RADIO-----Drake L-4B-----SWR METER-------Dummy load

Now the SWR stays low when I turn on the Drake L-4B for both the 1 KW
dummy load and the external antenna.

The transistor uses MRF455 transistors. Why would the SWR meter go up
significantly when I turn on the 2 transisor amp, but stay low when I
turn on a Drake L-4B.

I've duplicated this scenario with three different SWR meters, and
different patch cables. Lets me say for the record the SWR meter
comes after the amp, so I'm not looking at a high SWR on the input
side of the amp. This is on the output side of the amp.

?????

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.