Hello Mark,
Yes I do read most postings on this reflector. It is a great group.
I think there is likely over 1000 of the Hi-Z amps around the world. I have no
direct knowledge of any amp damaged from locally transmitted RF with one
exception. We tried it with a lot of power really close. One fellow in EU tried
to make a combination Hi-Z array and 30 meter transmit array all in one
footprint? Poof! Yes, the amps have unique circuit design internally to protect
themselves. That is one of the reasons there is 4 to 5 Volts DC on the antenna
elements during normal operation. There is also an internal relay that grounds
the antenna through a 1/4 watt resistor when the power is removed. This is
there for lightning protection where one turns the array power off when not in
use. It is not necessary to remove power during your transmitting or normal
use. Yes, we have had units come back or be repaired in the field that have
that resistor burned out when the rest of the circuitry remained calibrated and
fully operational. Cheap insurance.
There is a 75 ohm post combining preamplifier that can also handle your TX
voltages during transmit. The only caveat with it is you cannot short the
output of the arrays during transmit as that preamp will try to put all that RF
from your transmitter into a short circuit. It will blow the 2N3866 transistor
used in that preamp.
Lastly you should be aware that with your TX array this close to the RX
array you will have interaction likely causing pattern distortion during RX.
One way to deal with that is to detune the TX elements during RX. I suggest you
contact Gary KD9SV about detuning towers. He also makes front end protectors
always a good idea.
Lee K7TJR
Hi-Z Antennas
Subject: Topband: Hi Z 4 el. RX array LNA protection
Don’t recall if the owner of Hi Z monitors this site.
Question
Is there any protection for the individual LNA’s for strong signals? Am
planning to add a RX protector where it connects to the RX antenna port and of
course that that does not protect the LNA’s.
As much as I would love to put the array many hundreds of feet from the TX
antenna, it’s just not possible. Please advise! Thanks
Regards,
Mark, K1RX
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