At 12/22/2005 20:00, you wrote:
>On Thu, 22 Dec 2005, Reza PWW wrote:
> > Can anybody can advise me for tunning duplexer with minimum tools? For
> > example case: I have to change TX-RX frequensi in some place, where I
> > only have SWR and some HT and volt meter?
>
>A case of beer, an SWR meter, and a radio. Tune for minimum SWR. The case
>of beer is to insure accuracy -- largely because there isn't much. You're
>tuning for minimum insertion loss at that point (technically return loss).
>
>Really, you should find a friend with an IFR, communications analyzer, or
>spectrum analyzer with a tracking generator. To properly do the job, you
>need a dummy load on the unused port. Impedance mismatches can also do a
>job on cavity performance.
Seriously, you can tune the duplexer passes with a TX & wattmeter, but you
MUST also use an isolator between the test TX & duplexer so that the
duplexer sees 50 ohms in that direction. Also don't forget the 50 ohm
termination on the untested port of the duplexer.
This only gets you the passes. For the notches there's probably no getting
around needing some sort of well-shielded signal generator. If you try
transmitting into the duplexer at the notch frequency at say 10 watts (+40
dBm) & the duplexer notch depth is 80 dB, you'll get -40 dBm at the other
end. -40 dBm is too much signal to measure on an amateur transceiver (the
S-meters on my Yaesus max out around -90 dBm) yet not enough to drive a
wattmeter. Then there's the (lack of) shielding issues of HT & mobile radios.
If you're really intent on obtaining duplexer tuning capability for cheap,
invest in a old signal generator like the old dependable Singer FM-10 or
Wavetek 2407 or 2410. Don't forget the isolator & a good 10 dB pads for
the sig. gen. and test receiver to make darn sure all I/O looks like 50
ohms. Such a setup won't let you see everything that's going on like a
network analyzer or spectrum analyzer with tracking generator will (I've
done it both ways; both are accurate but the analyzer method is much faster
& more fun!).
Bob NO6B
Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/Repeater-Builder/
<*> To unsubscribe from this group, send an email to:
[EMAIL PROTECTED]
<*> Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/
