Say Tim;
If you have all of that rust it seems like besides high
resistance for proper contact wouldn't it cause some sort of leakage for
that desense problem, as well radiate some percentage of interference ?
even though you turned the power down, I was wondering how much work it
would be to replace that connector, I am guessing it was riveted in during
production.
MH
----- Original Message -----
From: "Tim S." <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Thursday, September 30, 2004 2:16 AM
Subject: [Repeater-Builder] The duplexer story...
> As I stated a few times here I have a duplexer that has been giving me
> desense. To get rid of the desense I turned down the TX power until it
went
> away because the duplexer is rusty and hasn't been messed with in 20+
years.
>
> I came across another duplexer in a base station cabinet we had and pulled
> the duplexer out. Here are the specs of it:
>
> TPRD-14744 (470-512 MHz)
>
> Type: 4 cavity pass-reject
>
> Minimum freq. spacing 3 MHz
> Insertion loss 1.0 dB
> Max. continuous power 250 watts
> TX noise supp. at Rx freq. 90 dB
> Rx isolation at TX freq. 90 dB
> Temperature range -30 to +70C
>
>
> I used the tracking generator and tuned and notched it on frequency.
>
> My plan was to use this duplexer as a backup if the original one would not
> tune.
>
> When I checked desense on the original again it was around 10db. I pulled
> the duplexer and found the reject was only about -75db on both sides.
>
> I adjusted the notches and got it down under -90db but noticed it jumped
> around -95db then -90db, etc... I did use double shielded cables for
> tuning.
>
> I checked the passes and they seemed ok, so I did not touch them.
>
> Put it back in place and turned the power back up from 15 watts out of the
> PA to 42 watts out of the PA.
>
> The desense jumped big time to around 20db.
>
> So I pulled the old duplexer and put in the spare.
>
> Now I have no measurable desense. So that's a plus.
>
> However, I put the service monitor on the PA output and read 42 watts.
> Hooked the cabling up to the duplexer and then checked the output of the
> duplexer and only read 22 watts. That's like a -2.8db loss.
>
> I didn't think at the time to check the interconnect cable from the PA to
> the duplexer, but I can't imagine that having a -1.8db loss. Since the
> duplexer should only have -1.0 db insertion loss.
>
> When I tuned the replacement I double checked all the peaks locked them
down
> then did the rejects. So I am pretty confident the duplexer is set right.
>
> So, in the end the repeater went from 15 watts out of the duplexer with
10db
> desense to 22 watts out with no desense.
>
> 1. Can something in the original duplexer go bad internally to cause the
> desense? Or must my tuning be suspect?
>
> 2. Think I need to worry about the -2.8 db power loss? All I can think
of
> doing is checking the interconnect cable from the PA to the duplexer
input.
> Another note: When I retuned the base station duplexer, I kept the low
side
> low and the high side high, meaning I am now transmitting on what was
> originally the RX port since it went from a base station use to repeater.
> Could this be a problem if I really have -2.8db insertion loss?
>
> -Tim
>
>
>
>
>
>
>
>
>
> Yahoo! Groups Links
>
>
>
>
>
>
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