Gervais,
Go to this eBay auction to view a picture:
Click on the third picture down - it's a MICOR VHF PA in a
station.
The BNC connector on the left is the RF input connection - the one
on the right is the RF output.? 12 - 16 Volt DC Power is connected
into the screw terminals in a obvious way.
The thin black wire connected under the input connection is the
switched A- (A minus) lead.? The wire could be any color - on this
station it's black.
For your application, that lead needs to be connected to ground
when the PA is intended to make power (during transmit).? It is
left open circuit when the transmitter is inactive.? A switched
ground can be accomplished many ways:
1 - A relay with its coil sourced from the PTT signal of the
controller.
2 - Directly from the repeater controllers PTT signal *.
3 - A NPN switching transistor with an inverter in front of it
sourced from the PTT feeding the base with sufficient current to
saturate it.
4 - Wire the switched A- lead to ground - and forego switching it.
#
* Not all repeater controllers can handle the current draw
necessary for the PA's switched A- connection.
# Not recommended - as the power amplifier could cause
interference when the exciter isn't making power.
Kevin
On 1/5/2025 5:35 PM, Gervais Fillion via groups.io wrote:
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Well,
great answers but i dont understand everything ,,i am not a tech
as you guys!
If i understand ,on the Micor PA i could connect some wires (on
the PA circuit) so at the ainstant 250 mw would be
applied,detected? it would ,,,transmit ??
on my Master 2 PA that i add it was like that,if i applied 300mw
it would amplified and bingo the repeater was On the air.
excuse me to be to ,,,simple in my explanation !
i may end by buying an rf amplier on Ebay? but they will never
be as HD as the true repeater PA.
73/s and Best 2025 to all!
Gef
Ve2ckn
Karl,
The information you provided to Gervais is NOT correct.
On a MICOR VHF power amplifier - you have to switch the A- (A
minus) during transmit.? This logic can be sourced from the
PTT of the repeater controller.? In other words A- needs
grounded during transmit.? A- is a connection on the side of
the PA - and usually has a wire attached that plugs onto the
station.? This can be easily accomplished using a relay or
transistor sourced from the PTT logic.? Some repeater
controllers can provide the logic directly as the current is
not excessive.
----
The drive power level between a GE MASTR II VHF PA and a
Motorola MICOR VHF PA is EXACTLY the same.?
GE Exciters put out 200mW and have nothing between the exciter
and power amplifier.? Therefore the power amplifier has an
input power level of 200mW.
Motorola MICOR VHF Exciters put out 400mW but an exciter
band-pass filter that has 1.5 to 3dB insertion loss exists in
between the exciter and PA.? As such - about 200mW is
delivered from the BP filer to the input of the power
amplifier.? Therefore, the Motorola MICOR VHF power amplifier
is properly driven with a GE MASTR II exciter with nothing in
between.
Kevin
On 1/5/2025 2:02 AM, Karl Shoemaker via groups.io wrote:
Gervais, ? The Motorola PA B- has to be switched in
order for the amplifier to work (unless you modify it like
I do). ?If you do have a "hot" PA be sure to protect it
with an isolator and cavity if you are at a populated
site.?
Also, RF power input standards are different between GE
and Motorola; +23 and +26 dbm, respectively.? Best way to
blow an amplifier is over driving it.
?
GE PA's can be repaired if you can find the parts and
properly troubleshoot it. The hardest part to find may be
the power control module. It's either blue or black on the
outside with many pins.
So, isolate if it's a (power) transistor(s) or an
IC-control problem. Also, the braid or strap between the
boards have a habit of opening up. That's near the filter
board. ?
?
Heat is not so much the big issue here, it's the
extreme hot and cold cycling that destroys semi-conductors
and other components
-
Regards, Karl Shoemaker
To contact me, please visit SRG's web site at?
for the current email address.
Kevin Custer