Yes... I'm the designer. I used Pcad software for schematic capture and
PCB layout.

Professor
Check out FlashAlert at www.telstar-electronics.com

On 17 Jul 2005 06:51:02 -0700, "Professor"
wrote:

Yes... I'm the designer. I used Pcad software for schematic capture and
PCB layout.

Professor
Check out FlashAlert at www.telstar-electronics.com

I've been looking at the design of several amps, and all amps are
definitely not created equal. The regulated bias supply is seldom
seen in the CB amp world.
I picked up a Palomar Elite 300 for study. It turned out to be a
study in what not to do.

Here is what I found so far;

1) The amp is zero bias. Sounds like Darth Vader with added distortion
on sideband.

Ok. I fixed that with a diode clamp. At least mine is in AB1 now.

2) The low and medium power setting is achieved by sending some of
the RF to ground via a single resistor. The input SWR goes through
the roof.

Ok. I replaced that with a 50 ohm impedance resistive t-pad.

3) The SWR delay is on all the time, and sometimes people responding
to my transmit get chopped off in my receive before the amp's relay
can un-key.

Ok. I put the delay capacitor for the relay on a switch.

4) Here is the weird one. The SWR without the amp on is 1.1, but
when I turn the amp on the SWR goes to 3.x:1 or higher, and I'm
talking about the SWR displayed on a meter AFTER the amp. Not the SWR
on the input side of the amp.

Hmm. This one stumped me, but some other smart fellows suggested the
amp has parasitic oscillations and the frequency (or frequencies) of
the oscillation(s) are outside the bandwidth of the antenna. I can
take another amp with two 3-500z tubes, and put it on the same antenna
with no substantial increase in SWR from the antenna. The Palomar
Elite 300 is only good for about 100 watts. The two 3-500s are good
for 1300 watts. The antenna is rated at 5000 watts.

I'm still working on the fix for this one. Tuned input and output
circuits would probably fix it, but there is not alot of space inside
the amp to work with.

5) The RF from the output transformer is not filtered from the DC
input to the collector on the finals.

Ok, I put an RF choke on the DC power cables to keep the RF from
running up the DC cables and tripping out my pwer supply.

On 17 Jul 2005 06:51:02 -0700, "Professor"
wrote:

Yes... I'm the designer. I used Pcad software for schematic capture and
PCB layout.

Professor
Check out FlashAlert at www.telstar-electronics.com

PCad 2004

-------------------
Retail price US Dollars
New P-CAD 2004 Full Suite License $9,995
Upgrades to P-CAD 2004 Full Suite Prices from $2,995
Other P-CAD New License Configurations
P-CAD 2004 (6L400C) $5,995
P-CAD 2004 Schematic $1,695
---------------------

Ouch!

On Sun, 17 Jul 2005 17:29:19 GMT, 800 Whiskeys
wrote in :

On 17 Jul 2005 06:51:02 -0700, "Professor"
wrote:

Yes... I'm the designer. I used Pcad software for schematic capture and
PCB layout.

Professor
Check out FlashAlert at www.telstar-electronics.com

I've been looking at the design of several amps, and all amps are
definitely not created equal. The regulated bias supply is seldom
seen in the CB amp world.
I picked up a Palomar Elite 300 for study. It turned out to be a
study in what not to do.

Here is what I found so far;

1) The amp is zero bias. Sounds like Darth Vader with added distortion
on sideband.

Ok. I fixed that with a diode clamp. At least mine is in AB1 now.


Check the idle current on the collector -- you might be suprised.


2) The low and medium power setting is achieved by sending some of
the RF to ground via a single resistor. The input SWR goes through
the roof.

Ok. I replaced that with a 50 ohm impedance resistive t-pad.


Fine if the resistors are non-inductive and can handle the power
dissipation.


3) The SWR delay is on all the time, and sometimes people responding
to my transmit get chopped off in my receive before the amp's relay
can un-key.

Ok. I put the delay capacitor for the relay on a switch.


Assuming you meant SSB delay, ok. A better way is to modify the radio
to superimpose a high-Z DC on the output when keyed (in AM -and- SSB),
then rig the amp relays to switch on that DC signal.


4) Here is the weird one. The SWR without the amp on is 1.1, but
when I turn the amp on the SWR goes to 3.x:1 or higher, and I'm
talking about the SWR displayed on a meter AFTER the amp. Not the SWR
on the input side of the amp.

Hmm. This one stumped me, but some other smart fellows suggested the
amp has parasitic oscillations and the frequency (or frequencies) of
the oscillation(s) are outside the bandwidth of the antenna. I can
take another amp with two 3-500z tubes, and put it on the same antenna
with no substantial increase in SWR from the antenna. The Palomar
Elite 300 is only good for about 100 watts. The two 3-500s are good
for 1300 watts. The antenna is rated at 5000 watts.

I'm still working on the fix for this one. Tuned input and output
circuits would probably fix it, but there is not alot of space inside
the amp to work with.


The reason for this problem is obvious -- the output impedance of the
amp is not even close to 50 ohms. It's that simple.


5) The RF from the output transformer is not filtered from the DC
input to the collector on the finals.

Ok, I put an RF choke on the DC power cables to keep the RF from
running up the DC cables and tripping out my pwer supply.


A warning about chokes -- almost all of them are self-resonant at some
frequency; and with stray capacitance in the circuit (including the
power leads) they can set up resonance on even more frequencies.






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On Sun, 17 Jul 2005 13:08:44 -0700, Frank Gilliland
wrote:

Here is what I found so far;

1) The amp is zero bias. Sounds like Darth Vader with added distortion
on sideband.

Ok. I fixed that with a diode clamp. At least mine is in AB1 now.


Check the idle current on the collector -- you might be suprised.



The collector had no connection of any kind back to the B+. It only
had a ferrite bead going to ground. It was entirely up to in the rf
input signal from the radio to turn on the transistor.


4) Here is the weird one. The SWR without the amp on is 1.1, but
when I turn the amp on the SWR goes to 3.x:1 or higher, and I'm
talking about the SWR displayed on a meter AFTER the amp. Not the SWR
on the input side of the amp.

Hmm. This one stumped me, but some other smart fellows suggested the
amp has parasitic oscillations and the frequency (or frequencies) of
the oscillation(s) are outside the bandwidth of the antenna. I can
take another amp with two 3-500z tubes, and put it on the same antenna
with no substantial increase in SWR from the antenna. The Palomar
Elite 300 is only good for about 100 watts. The two 3-500s are good
for 1300 watts. The antenna is rated at 5000 watts.

I'm still working on the fix for this one. Tuned input and output
circuits would probably fix it, but there is not alot of space inside
the amp to work with.


The reason for this problem is obvious -- the output impedance of the
amp is not even close to 50 ohms. It's that simple.


Just in case you were right, I tried changing the number of windings
on the broad band output transformer, but it still did not get rid of
the SWR after the amp. There were some number windings that the meter
showed more output on than others, but the reflected power back from
the antenna varied proportionally with it. I think the other guys are
right in suggestion the amp is generating frequencies outside of the
bandwidth of the antenna, and those out of band frequencies are
generating the reflected power back from the antenna.
An SWR meter hooked up after the amp should be measuring the
reflected power back from the antenna verses the forward RF coming
from the amp. I don't see how the amp could cause reflected power
back from the antenna due to an impedance mismatch inside the amp when
the SWR meter is hooked up between the amp and the antenna. The coax
is 50 ohms even of the amp is not, and the reflected power back from
the antenna is caused by an impedance mismatch between the coax and
the antenna.
If you can logicaly explain how an impedance mismatch in the amp can
cause reflected power back form the antenna I am more than willing to
listen. On the truth with fix this amp, but I really don't see how an
impedance mismatch before the SWR meter can cause reflected power back
from the antenna.


5) The RF from the output transformer is not filtered from the DC
input to the collector on the finals.

Ok, I put an RF choke on the DC power cables to keep the RF from
running up the DC cables and tripping out my pwer supply.


A warning about chokes -- almost all of them are self-resonant at some
frequency; and with stray capacitance in the circuit (including the
power leads) they can set up resonance on even more frequencies.






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On Sun, 17 Jul 2005 22:58:35 GMT, 800 Whiskeys
wrote:

On Sun, 17 Jul 2005 13:08:44 -0700, Frank Gilliland
wrote:


The collector had no connection of any kind back to the B+. It only
had a ferrite bead going to ground. It was entirely up to in the rf
input signal from the radio to turn on the transistor.

I'm sorry. I made a mistake. The above should have read;

The base had no connection of any kind back to the B+. It only
had a ferrite bead going to ground. It was entirely up to in the rf
input signal from the radio to turn on the transistor.

Yes... that package is not cheap. There are certainly others out there
that might suit your needs. You might try this... free software... and
I have purchased many PCBs from this company. http://www.pcb123.com/

Professor
Check out FlashAlert at www.telstar-electronics.com

On Sun, 17 Jul 2005 22:58:35 GMT, 800 Whiskeys
wrote in :

On Sun, 17 Jul 2005 13:08:44 -0700, Frank Gilliland
wrote:

Here is what I found so far;

1) The amp is zero bias. Sounds like Darth Vader with added distortion
on sideband.

Ok. I fixed that with a diode clamp. At least mine is in AB1 now.


Check the idle current on the collector -- you might be suprised.



The collector had no connection of any kind back to the B+. It only
had a ferrite bead going to ground. It was entirely up to in the rf
input signal from the radio to turn on the transistor.


Correction in follow up post noted, but you should still check your
idle collector current.


4) Here is the weird one. The SWR without the amp on is 1.1, but
when I turn the amp on the SWR goes to 3.x:1 or higher, and I'm
talking about the SWR displayed on a meter AFTER the amp. Not the SWR
on the input side of the amp.

Hmm. This one stumped me, but some other smart fellows suggested the
amp has parasitic oscillations and the frequency (or frequencies) of
the oscillation(s) are outside the bandwidth of the antenna. I can
take another amp with two 3-500z tubes, and put it on the same antenna
with no substantial increase in SWR from the antenna. The Palomar
Elite 300 is only good for about 100 watts. The two 3-500s are good
for 1300 watts. The antenna is rated at 5000 watts.

I'm still working on the fix for this one. Tuned input and output
circuits would probably fix it, but there is not alot of space inside
the amp to work with.


The reason for this problem is obvious -- the output impedance of the
amp is not even close to 50 ohms. It's that simple.


Just in case you were right, I tried changing the number of windings
on the broad band output transformer, but it still did not get rid of
the SWR after the amp. There were some number windings that the meter
showed more output on than others, but the reflected power back from
the antenna varied proportionally with it.


You are forgetting that impedance = resistance + reactance. Your
transformer may have the right number of turns, but the collectors of
the transistors are very reactive and that reactance is reflected to
the amp's output through your transformer. You need to cancel out that
reactance. That's why SS amps have a large capacitance on the output
end of the transformer (no, those caps aren't there to make a tuned
output tank).


I think the other guys are
right in suggestion the amp is generating frequencies outside of the
bandwidth of the antenna, and those out of band frequencies are
generating the reflected power back from the antenna.


If the amp was oscillating you would have probably smoked your
transistors by now.


An SWR meter hooked up after the amp should be measuring the
reflected power back from the antenna verses the forward RF coming
from the amp. I don't see how the amp could cause reflected power
back from the antenna due to an impedance mismatch inside the amp when
the SWR meter is hooked up between the amp and the antenna. The coax
is 50 ohms even of the amp is not, and the reflected power back from
the antenna is caused by an impedance mismatch between the coax and
the antenna.
If you can logicaly explain how an impedance mismatch in the amp can
cause reflected power back form the antenna I am more than willing to
listen. On the truth with fix this amp, but I really don't see how an
impedance mismatch before the SWR meter can cause reflected power back
from the antenna.


Forget the coax for a moment: If your forward power is highly reactive
(as I suspect) and it's feeding an essentially non-reactive load, the
result is an impedance mismatch, and therefore you will have reflected
power. What you do is hook your amp to the directional coupler and a
non-reactive dummy load (using SHORT cables), then adjust the amp's
output capacitance (as stated earlier) for a 1:1 SWR.









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On Sun, 17 Jul 2005 13:08:44 -0700, Frank Gilliland
wrote:


4) Here is the weird one. The SWR without the amp on is 1.1, but
when I turn the amp on the SWR goes to 3.x:1 or higher, and I'm
talking about the SWR displayed on a meter AFTER the amp. Not the SWR
on the input side of the amp.

Hmm. This one stumped me, but some other smart fellows suggested the
amp has parasitic oscillations and the frequency (or frequencies) of
the oscillation(s) are outside the bandwidth of the antenna. I can
take another amp with two 3-500z tubes, and put it on the same antenna
with no substantial increase in SWR from the antenna. The Palomar
Elite 300 is only good for about 100 watts. The two 3-500s are good
for 1300 watts. The antenna is rated at 5000 watts.

I'm still working on the fix for this one. Tuned input and output
circuits would probably fix it, but there is not alot of space inside
the amp to work with.


The reason for this problem is obvious -- the output impedance of the
amp is not even close to 50 ohms. It's that simple.


Actually the other guys were 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 installed, but with the low pass filter installed and the watt
meter connected after the low pass filter the output 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 transistor
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
transistor base to ground and the SWR with the amp dropped to 1.3:1
with the amp on.

Re-inserting the low pass filter in between the amp and the SWR meter
showed 1.1:1 with and without the amp on, so some harminoc content was
still be transmitted but to a lesser extent.

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.

RESOLUTION: The SWR increased was caused by harmonics above the
fundamental frequency, and they were outside the bandwidth of the
antenna.

Lessons learned....

1) Just because your amp shows 100 watts output does not mean that 100
watts is being transmitted on the frequency you are on. It may be
less, and if the amp is poorly designed it could be alot less.

2) If your SWR goes up when you turn an amp on it could be because
your amp has increased the harmonic output of your transmitted in a
non-linear fashion.

3) If installing a low pass filter between your amp and the watt meter
causes the wattage displayed on the watt meter to drop it is probably
because you amp is wasting power on frequencies far above your main
fundamental frequency.


4) If you go to the trouble of re-designing the Palomar Elite 300 amp
and clean up all the dirty output your real output power on the
frequency you are listening to will only be about 70 watts RMS tops,
and even then you are over driving the amp.

...and lastly...

The Palomar Elite 300 is a poorly designed piece of crap. Don't buy
one.

Your right 800Whiskey... harmonic content is important. Most of the
amps out there are very dirty... even if they have some biasing
(although 95% have no DC bias at all). This is done because proper
biasing methods add cost... and the potential market of buyers for
these products don't demand good harmonic performance.

Professor
www.telstar-electronics.com