[SBE] Question about an FM translator cavity filter --

[Ron Castro]

The first thing to do is sweep the filter and make sure it's aligned.  It's 
possible that the BR might be a bit too close to the transmit frequency.  BP 
filters can be adjusted to give narrower bandwidth, but at the expense of 
greater loss, and given the proximity of the channels involved, 6 to 7 dB 
may be within specifications.  That means that you need 4-5 times TPO to 
make your licensed ERP than if you didn't have the filter, and if there is 
any way to eliminate the filter by moving the receive antenna farther away 
from the transmit antenna, or to explore an alternative feed method, you'll 
be much better off.  Filters that narrow can cause significant phase shift 
across the bandpass, resulting in what is generally called phase-induced 
multi-path.  It's not actually multi-path, but sounds like it.

What kind of front-end filtering is on the receiver?

         Ron Castro
 Chief Technical Officer
    Results Radio, LLC
               N6IE
      www.N6IE.com


----- Original Message ----- 
From: "Mike Langner" <mlangner at swcp.com>
To: <sbe at sbe.org>
Sent: Monday, June 02, 2008 6:57 PM
Subject: [SBE] Question about an FM translator cavity filter --



> Hello all !

>

> I am working on improving the performance of an FM Broadcast Translator 

> that

> is using a Remec Wacom BPBR filter in its output.

>

> The three cavity filter is model WP-715D-3, it is serial number 4515.  It 

> is

> set to pass 95.8 - 96.0, and to reject 95.4 - 95.6.

>

> The translator receives on 95.5; it transmits on 95.9.  (Ouch !  Close

> spacing!)

>

> The filter exhibits about 6 to 7 dB loss on-channel.

>

> Would anyone have catalogue info or a data sheet on this item?  I sent an

> email to the manufacturer (sales at txrx.com) which was the only email 

> address

> I could find, and have received no answer after a week or so.  I 

> understand

> that TXRX is the successor-in-interest to Wacom, but perhaps I am mistaken

> and someone can correct me.

>

> Could some kind person please tell me if what I'm experiencing (waaaaay 

> more

> on-channel loss than I'd like) is what I should expect from this unit?

>

> Thanks very, very much !

>

> Mike Langner, CPBE

> Albuquerque, NM

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