Hello,
The question: What is the maximum voltage I can put into the antenna
bias connection?
The possible mod or configuration jumper:
I have a WR-LNA-3500 preamplifier that can be powered by coax or a
coaxial power connector. There is a diode to prevent backfeeding power
through the receiver port if the coaxial power connector is used. There
is no shunt resistor to prevent diode leakage current from building up a
voltage on the receiver port. I measure 13.2 volts on my high impedance
DVM at the receiver port with the preamplifier powered.
In looking at the schematic of the DBSRX I noticed there is no real DC
path to ground when DC Bias is not used. Would there be any problem to
either jumper the DC Bias connector when not used or to add a high value
shunt resistor across the DC Bias connector to keep any DC levels down?
I assume the choke will keep most of the RF on the proper side.
73 Eric
In looking at the schematic of the DBSRX I noticed there is no real DC path to ground when DC Bias is not used. Would there be any problem to either jumper the DC Bias connector when not used or to add a high value shunt resistor across the DC Bias connector to keep any DC levels down? I assume the choke will keep most of the RF on the proper side.
Shorting J101 puts 5 Volts (up to 500 mA I believe) on the antenna line.
Applying voltage to J100 pin 1 allows you to send bias other than 5V.
The DC-blocking cap to the LNA should be good to 50V, but I wouldn’t
push it.
Shorting across J100 would give a DC short to your amplifier, which
seems ok from the DBSRX side, but make sure your amp won’t send
significant current down that line.
Matt
----- Start Original Message -----
Sent: Wed, 11 Jul 2007 15:58:09 -0700
From: Matt E. [email protected]
To: Eric C. [email protected]
Subject: Re: [Discuss-gnuradio] DBSRX Modification and Antenna Bias
Question
Shorting across J100 would give a DC short to your amplifier, which
seems ok from the DBSRX side, but make sure your amp won’t send
significant current down that line.
Matt
----- End Original Message -----
Hello,
Thanks. Maybe it would be safer to put a 10k or 100k resistor across
there. I can just picture the damage if the diode in the preamplifier
ever failed.
I managed to change the DBSRX LNA chip on my second attempt. I managed
to lift the pad on the input side so I had to jumper from the capacitor
to Pin 3. Actually the second attempt was quicker and easier. So I got
8 LNA spares that will be lost the next time I need them. I just need
to test the board when I get home. Hopefully the board will get a
second life but I doubt it will get a third.
After this experience changing that huge surface mount GAs MESFET in the
AR5000 will be a piece of cake.
73 Eric