Thanks so much Joe. I think your recommendation on filtering the output of
the UHF repeater seems to make good since to me. We will start there. The
duplexer is one of the smaller units as compared to the larger cans I have
seen for UHF. I guess it is different designs. I know I have seen some UHF
duplexers at Hamfest that where much smaller than our two meter stuff of
course, but still much larger than the unit we are using. I don't know the
difference, I assumed just different design technology, and not necessarily
bigger is better. If I am wrong on that part, please let me know, because I
have access to a UHF duplexer, the 4 can type (probably 4"X8" or 10" tall,
for a fairly small investment. I will first look into the exact filter you
suggested. It makes since to me it is better to clean up the signal
transmitted as much as possible anyway. Then we will follow your suggestions
on the link radio receiver next as you have suggested if the problem
persist. Thanks a billion to you and the group for all the help.
 

73 de  John Godfrey
KE5NZY BARC Pres.


 
 -----Original Message-----
From: Repeater-Builder@yahoogroups.com
[mailto:repeater-buil...@yahoogroups.com] On Behalf Of Joe Burkleo
Sent: Sunday, May 03, 2009 1:42 AM
To: Repeater-Builder@yahoogroups.com
Subject: [Repeater-Builder] Re: Linking and interference problem





John,
Thanks for the more in-depth explanation.

Link antenna and feedline is about as good as you can get.

About the only improvement you might make is to get the two UHF antennas
directly under each other. That creates a cone of silence and make for the
best null.

No need for the 7/8" other than a small improvement in signal loss. I would
think about replacing all of the jumpers with silver plated double shielded
coax.

The filter that comes to mind for your link receiver would be a very precise
crystal filter made for your link radio receive frequency. They are kinda
pricey, so they may be out of your price range, but they are only a few KC
wide. Since it sounds like the hub repeater is on a stable frequency and
will most likely be there for a long time, the crystal filter makes sense.
They are not re-tunable in the field since they are made for a very specific
receive frequency. They have a little loss in them, but since you can run
the squelch fully tight, you have enough headroom, and that should not be a
problem.

Other item I would recommend is to install a isolator on the UHF repeater
transmitter before it gets to the duplexer. I am not sure what you are using
for a duplexer, but I also might suggest locating a Telewave or similar 9"
diameter to 12" diameter bandpass filter (one that has two connectors) to go
between the UHF repeater transmitter and the duplexer. They use these large
diameter UHF cavities for transmit combiners, but I have seen them on Ebay
for reasonable prices from time to time. The larger diameter the cavity, the
steeper the skirts on each side of the transmit frequency will be.

I know this may sound backwards, but I would attack adding the isolator and
additional filtering on the UHF transmitter as the first step. Once you have
made the UHF repeater transmitter as clean as it can be, then you can move
on to adding any additional filtering to the link receiver, if it is still
needed.

Joe - WA7JAW

> Joe, Thanks for asking..
> 
> Question #1 link antenna is on top. 8 element yagi vertical pointed 210 SW
> 
> Question #2 No. They are on different legs and each is on the other side
of
> the tower, almost directly opposite each other.
> 
> Question #3 No preamp.
> 
> Question #4 1/2 inch Andrews Heliax (not superflex) on both UHF units
150FT
> on one 140Ft on the other. 3ft jumpers 9914 belden on each radio. same on
> the Yagi's. N type connectors. Wish we could afford 7/8, but we take what
> the club can afford and work with that. Our club has appox 50 members,
> sometimes more or less depending on when they pay there dues. Hi HI. I
know
> you didn't ask, but just in case you needed to know, 7/8 is not an option
> for us right now.
> 
> Agreed that even just a few extra db rejection would do the trick. It
> wouldn't take a lot I don't think based on the squelch test, but a few db
I
> would be highly thankful for, and I just don't have the knowledge to know
> how to get there from here. (-:
> 
> 73 de John Godfrey
> KE5NZY BARC Pres.
> 





Reply via email to