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

[Mike Langner]

These are great ideas !

But. . .

While I could put a receiver somewhere else on the small electronic site on
the mountain, there's no way to get very far from the very short-tower 25 kW
FM station just 1.2 MHz away!

And the FM station does not have a cleanup cavity in its output. To meet FCC
spec, it doesn't have to -- but a signal that strong "strobes" every poor
connection, dissimilar metal joints, and bores its way into receiver front
ends with enough signal to put the current "loaner" translator's front end
out of linearity -- a classic case of fundamental overload. So, I've
filtered everything I can -- but not being able to control what's made in
adjacent sites in the very small area is a real headache!

I sent the local translator association a small helical notch filter that
will get rid of a bunch of the high-power FM station, and hopefully getting
the front end of the receiver back into its linear region will "fix" many of
the problems.

As for the transmit side, I think one clean-up cavity out to be enough.
Whoever spent way too much money on a three-cavity notch-pass was, I think,
sold something they really don't need.

The temporary transmitter (while I re-cap the permanent one) has "electronic
tuning" in its front end.  That it's frequency-agile is really handy -- but
nothing beats real cavities and real helical filters.  The older "permanent"
translator can withstand the "electronic fog" at the site much better -- it
has real physical/mechanical tuned circuits, not varicaps across inductors.

So, I think the end is in sight.

Still, it would be interesting to know what the performance characteristics
of the filter somebody put in the line are supposed to be!  It would also be
interesting to know who put it there !!

Thanks again !!

Mike/
________________________


-----Original Message-----
From: sbe-bounces at sbe.org [mailto:sbe-bounces at sbe.org]On Behalf Of Bill
Whitt
Sent: Tuesday, June 03, 2008 6:20 PM
To: 'sbe member discussion mail list'
Subject: Re: [SBE] Question about an FM translator cavity filter --


Not that I know a huge amount about FM, but I wanted to relate to this issue
via the TV side. I had this problem when I lost my original channel number
to another company. I had to receive on 22 and transmit on 23. The original
unit I had on the mountain was a translator. I was having a heck of a time
setting up filters, adjusting my down convertor, and constantly adjusting my
forward power. One day, while I was lighting the match to burn down the
transmitter site ... I had an idea. I soon converted the turkey from a
translator to a transmitter ... using alternate devices to receive and break
apart my video and audio components. My figuring was if I was able to get it
from RF to its individual components ... I could clean them up and feed it
back into my transmitter stronger and tightened up. The result was better
than I could have imagined, plus I was able to eeekkk out more forward
power. Later on, I gained permission to relocate my receive antenna away
from the directional forward power of my transmit antenna. This improved my
situation that much more. I still have to watch my forward power ... but man
what a difference.

Hope this helps .. :-)

Bill Whitt

-----Original Message-----
From: sbe-bounces at sbe.org [mailto:sbe-bounces at sbe.org] On Behalf Of Mike
Langner
Sent: Monday, June 02, 2008 6:57 PM
To: sbe at sbe.org
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
_______________________________________________
SBE mailing list
To unsubscribe, go to http://seven.pairlist.net/mailman/options/sbe
_______________________________________________
SBE at sbe.org
http://seven.pairlist.net/mailman/listinfo/sbe

_______________________________________________
SBE mailing list
To unsubscribe, go to http://seven.pairlist.net/mailman/options/sbe
_______________________________________________
SBE at sbe.org
http://seven.pairlist.net/mailman/listinfo/sbe