[CQ-Contest] RE:What RF voltage OK at Rx in SO2R?

PETER BARRON ve3pn at igs.net
Tue Sep 25 06:33:56 EDT 2001

Hi Jerry

Suggest running tests in two sections

A 	At 1 W (+30dBm) into one antenna measure the levels at fundamental and
the harmonics on another receiver or preferably a RF Voltmeter. E.G. Fire up
into the 80M antenna and measure on the 40/20/15/10M antennas AND BEVERAGES
Repeat for each TX antenna as source.
A calibrated or known S meter helps here i.e. one of mine gives
S9=34microvolts or -73dBm (or 103 dB down from 1W)

B	Fire up the rig into a (shielded) dummy load at maximum power level and
repeat A.

Levels in B for fundamental and harmonics should be at least 90 dB below A ,
S9 +20 or higher (especially on harmonics)  is a potential problem and
cables and connectors should be checked. Aim to get all this below S9.

With test A tabulated slowly increase TX power and keep measuring the
fundamental and harmonics and keep looking for any non linear effect such as
harmonic jumps or steps,  Keep increasing power until the fundamental on
measuring RX reads S9+40 on fundamental.
Sharp jumps in harmonics indicate problems somewhere start looking at
connectors and soldering and tower sections and connections to any metal
object near the antennas.

Make sure the feed lines don't couple or touch grounding them every 100 ft
or so helps in may other areas as well.

This will give a good baseline to asses stubs and filter needs especially
for harmonics.

A good accurate low power meter can be made using an Analog Devices AD8309.

Peter A Barron
ve3pn at igs.net

Date:	Sun, 23 Sep 2001 10:43:25 -0400
From:	Jerry Flanders <jflanders2 at home.com>
Subject:	[CQ-Contest] What RF voltage OK at Rx in SO2R?

I am trying to set up for RTTY SO2R and have two questions:
1.	What voltage levels can solid state rigs safely tolerate from nearby TX?
2.	I read about guys using stubs as well as filters in SO2R. How much of
this is just to protect the Rx hardware, and how much is there to improve
normal Rx on band A while TX on band B is underway?

I would like to avoid smoke testing the Rx front ends on my FT-1000D and
IC-756PRO if possible. I intend to measure actual voltage present on my
(well separated) Rx antennas while transmitting and determine from that if I
actually need protection, and to what degree. This is aside from the
question of Rx overload, which I can see for myself once I get it all in
actual operation. My immediate goal is to see if I can safely TX w/o smoke
before I start working with stubs or filters.
Jerry Flanders  W4UK

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