[Repeater-Builder] Bandpass Duplexer Tuning Help

[Rich Garcia]

I have searched the RB home page and also the web for tuning help but am not
coming up with what I need. I am trying to make a 4 can bandpass duplexer
out of a couple of Waycom  WP-436's (Double Can packages). I have a Tracking
generator and am trying to come up with images of what it should look like
since this is the first time I have had access to the fancy stuff. I have
tuned up a set of them for the RX side but since this is my first time I am
a bit unsure.

I have a 3mb photo of the screen if anyone has some expirence using tracking
generators and can take a look at the image for me for suggestions. I may be
able to bump the resolution down a bit but I don't want the markers to get
fuzzy. If anyone has a moment to take a peek let me know and I will e-mail
it to you directly.

Thanks,
Rich






 
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Re: [Repeater-Builder] Bandpass Duplexer Tuning Help

[Eric Lemmon]

Rich,

I looked in my WACOM full-line catalog, and found no listing for a
WP-436; the list jumps from WP-430-3 to WP-438-1.  Both of these
Bandpass Cavities are for the 144-174 MHz band.  If you're certain about
the model number, please provide the dimensions of the cavity itself,
exclusive of the connectors and plunger hardware.  Also, does each
cavity have one or two connectors?

Bandpass cavities, by themselves, seldom provide enough isolation for
duplex operation.  At crowded sites, a bandpass duplexer is usually used
with separate antennas for TX and RX.  Otherwise, two or more notch
cavities are needed to take out the TX carrier while the bandpass
cavities reduce the sideband noise.

I must assume that you intend to use this duplexer on a repeater pair
that has either a 5.0 MHz or 5.26 MHz split, true?

Since you have a spectrum analyzer with a tracking generator, simply
adjust the center plunger rod for a peak at the frequency of interest. 
Be careful to verify that the frequency calibration of the analyzer is
right on the money. Now, adjust the loops for about 0.8 dB of insertion
loss per cavity.  Reverse the source and return connections several
times to ensure that the cavity tuning is symmetrical.  Once you have
two cavities tuned individually, connect them in series and verify that
the combined insertion loss is no more than about 1.7 dB.  If the
combined loss is significantly more than the summ of the individual
losses, the length of the jumper cable must be changed until the VSWR is
matched between the cavities.

This matching of cavity VSWR is made much easier with a return loss
bridge or a network analyzer, since you can achieve a match in a few
seconds.  Although a good RLB costs a few hundred bucks, it is worth its
weight in gold!

73, Eric Lemmon WB6FLY

Rich Garcia wrote:
 
... I am trying to make a 4 can bandpass duplexer out of a couple of
Wacom  WP-436's (Double Can packages). I have a Tracking generator and
am trying to come up with images of what it should look like...




 
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