Topband: Hi Z 4 el. RX array LNA protection

Lee STRAHAN k7tjr at
Sat May 4 12:25:39 EDT 2019

   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. 


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


Mark, K1RX

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