Tim, a couple of questions come to mind.
1.) Are you trying to tune a T-band Duplexer down to
440? Not reccomended.
2.) Are you running a circulator between the duplexer
and the antenna?
3.) Are you using the same cables out of the repeater
to connect to the duplexer (either one) and seeing a
change?
Barry
--- "Tim S." <[EMAIL PROTECTED]> wrote:
> 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
>
>
> [EMAIL PROTECTED]
>
>
>
>
_______________________________
Do you Yahoo!?
Declare Yourself - Register online to vote today!
http://vote.yahoo.com
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/
