|
|
High power T/R switch - RF Cafe Forums
|
JimB
|
Post subject: High power T/R switch
Posted: Mon Apr 10, 2006 12:23 pm
|
|
Joined: Mon Apr 10, 2006
12:07 pm Posts: 2 Location: Harrod, OH
|
Hello, I am currently working a job which
requires characterizing a high power transmit /
receive switch for the HF band (1MHz to 30 MHz).
It is all solid state with a blocking voltage of
greater than 500 V on the diodes (power exceeds
1KW) when the receive path is off. Because of this
high voltage, I am hesitant to connect my VNA to
the ports for measurement in the off chance that
a bump of the cable or connectors may cause a transient
which will damage the VNA. Does anyone have
experience with this type of measurement? Is a DC
block sufficient? Where do I get one rated that
high? Most are rated 50VDC. All comments and questions
are appreciated. I do plan on testing for
line transients using a scope probe to make sure
I don't get spikes when switching from transmit
to receive. By the way, my background is
in cellular and cable. Five watts is a lot of power!
_________________ Jim Beckford RF Engineer
|
|
|
|
|
nubbage |
Post subject:
Posted: Thu Apr 13, 2006 9:58 am
|
|
|
General |
|
Joined: Fri Feb 17, 2006
12:07 pm Posts: 268 Location: London UK
|
My experience, with 80KW radar T/R switches, was
no matter how effective the PIN diodes were (and
the spec was excellent, cutting edge) the greatest
risk was leakage energy around the switches through
ground loops. There was enough leakage energy for
the pico-seconds of switch time, and enough pulse
circulating current, to blow enough 2350 Schottky
mixer diodes to boost HP's share price. Somehow,
I recommend you break up the ground paths to ensure
that the ground loop leakage paths between input
(Tx) and output (Rx) have as high a resistance as
possible. Using a scope probe can be misleading
for the same reason: where do you clip the ground
of the probe? In one place you get a great reading,
in another you could break down crying when you
see the trace. There just doesn't seem to be a true
ground zero anywhere on the circuit.
|
|
|
|
|
JimB |
Post subject:
Posted: Thu Apr 13, 2006 10:39 am
|
|
Joined: Mon Apr 10, 2006
12:07 pm Posts: 2 Location: Harrod, OH
|
Thank you. I hadn't thought of the high power RF
leakage, but looking at the driving logic, I see
the client has a delay between switching out the
PA and switching in the receiver. I'll pass along
the idea about separating the ground loops as he
is in the middle of a new board turn. I have
talked to him concerning the high DC voltage. The
new layout will allow the bias to be set down to
50V for s-parameter extraction. The purpose of the
s-parameter sweep is to verify that there are no
resonant responses (unlikely) or connector, core,
PCB losses in the basic design. Certainly, at high
power, things may change but the idea is to get
the basic design correct. This, of course, assumes
that the diodes have little change from 50V to >500V
reverse bias. Thanks again.
_________________ Jim Beckford RF Engineer
|
|
Posted 11/12/2012
|
|
|