Let's not forget that most PAs are powered continuously, and it is the
exciter that is keyed on and off. Any signal that mixes in the PA will
likely be amplified at full power, regardless of whether the transmitter
is on or not. In order to prevent this from happening, it is
sometimes necessary
At 5/5/2004 05:34 PM, you wrote:
Let's not forget that most PAs are powered continuously, and it is the
exciter that is keyed on and off. Any signal that mixes in the PA will
likely be amplified at full power, regardless of whether the transmitter
is on or not.
If the (class C) PA isn't being
ranging from -110dBm to -90dBm.
Good Luck, and I would start looking at the tower...
Charles Miller
- Original Message -
From: Richard Sharp, KQ4KX [EMAIL PROTECTED]
To: Repeater-Builder@yahoogroups.com
Sent: Wednesday, May 05, 2004 9:35 AM
Subject: RE: [Repeater-Builder] 2m repeater IMD
Several years ago, I had a similar problem with AM stations 1510 and 910
that were 600 khz apart. They were both about 5 miles away from our
repeater. Our 146.94 repeater when it keyed up was hearing the audio
combination of both AM transmitters that were on during the day. The
problem went away
John Lloyd wrote:
Several years ago, I had a similar problem with AM stations 1510 and 910
that were 600 khz apart. They were both about 5 miles away from our
repeater. Our 146.94 repeater when it keyed up was hearing the audio
combination of both AM transmitters that were on during the day.
Hi
gang,
Our club was allowed
space (no cost) on top of a 400' tower using an existing 7/8" line. The
existing UHF antenna was replaced (by the club) with a PD220-2 (142~150 range)
antenna. The coverage is very good. However, on occasion when users
with HTs or during a squelch tail the
Richard,
That's exactly what I would do: Lower the antenna, out of the intense
RF field.
73, Eric Lemmon WB6FLY
Richard Sharp, KQ4KX wrote:
Our club was allowed space (no cost) on top of a 400' tower using an
existing 7/8 line... At the top of this tower is also six other
transmit antennas
It would be nice to run an intermod program to see if any combination of
800 channels produced a 'hit' near the 2M input.
Ssb
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of the
preamp.
73,
Bryan
-Original Message-From: Richard Sharp, KQ4KX
[mailto:[EMAIL PROTECTED]Sent: Tuesday, May 04, 2004 8:04
PMTo: Repeater-Builder@yahoogroups.com;
[EMAIL PROTECTED]Subject: [Repeater-Builder] 2m repeater
IMD issue
Hi
gang,
Our club was
allowed
Bryan,
No, I
don't have a preamp in the circuit - it would only make things WORSE.
Well, when I add additional cavities it doesn't get rid of the IMD because it's
being generated somewhere else. When I'm not using a cavity the IMD is all
over the VHF band at about -90dBm. However, when
Richard,
You said that the IMD is only there when YOUR TX in on. If this is the case
you may need an Isolator for your TX. I had a site that was getting eat
alive with IMD at 150 MHz only when the TX was on. Found out that the IMD
was being generated in the transmitter. Put an isolator on the
I am suprised 800 will show passing thru in highband cavities, I would
think moving down one rack is the smartest thing to try, as you noted it
will be a low cost trial.
Richard Sharp, KQ4KX wrote:
Hi gang,
Our club was allowed space (no cost) on top of a 400' tower using an
existing 7/8
Richard,
Have you tried installing a low pass filter between your 2 Mtr duplexer
and the antenna feed line?
I am talking about the large low pass filters that were found in the old
VHF Motorola base stations that were about 1 inch in diameter and about
14 inches long.
I have a similar situation
Well, I considered that too. However, after further study of isolators (and
discussing my situation with a manufacturer of isolators) I discovered that
a VHF isolator will not stop signals in the 800MHz range from passing
through it. An isolator should work great if I was dealing with several
PROTECTED]
Sent: Wednesday, May 05, 2004 9:35 AM
To: Repeater-Builder@yahoogroups.com
Subject: RE: [Repeater-Builder] 2m repeater IMD issue
Well, I considered that too. However, after further study of isolators (and
discussing my situation with a manufacturer of isolators) I discovered
At 10:35 AM 5/5/2004 -0400, you wrote:
Well, I considered that too. However, after further study of isolators (and
discussing my situation with a manufacturer of isolators) I discovered that
a VHF isolator will not stop signals in the 800MHz range from passing
through it. An isolator should work
Sharp, KQ4KX [mailto:[EMAIL PROTECTED]
Sent: Wednesday, May 05, 2004 9:35 AM
To: Repeater-Builder@yahoogroups.com
Subject: RE: [Repeater-Builder] 2m repeater IMD issue
Well, I considered that too. However, after further study of isolators (and
discussing my situation with a manufacturer of isolators
-Original Message-
From: Ken Arck
---What bothers me here about using a circulator is that you say it only
occurs when your TX is active. This doesn't sound like IM to me, as that
would occur regardless of whether the tx was active or not (IM is produced
when external RF comes down
are concerned.. Caveat Emptor!
Steve, AA5SG
- Original Message -
From: Richard Sharp, KQ4KX [EMAIL PROTECTED]
To: Repeater-Builder@yahoogroups.com
Sent: Wednesday, May 05, 2004 10:01 AM
Subject: RE: [Repeater-Builder] 2m repeater IMD issue
-Original Message-
From: Ken Arck
Duplexers with one loop in UHF do not do much at 800 Mhz - have 4
repeaters with WP678's on 2 antennas, abt 10 ft from 800 SMR transmit
antenna - horizontal - ended up placing decibel band pass 2 loop cans in
front of each receiver - to keep 800 from really desensensing the 460
recs. Uniden 460
At 11:52 AM 5/5/2004 -0500, you wrote:
Duplexers with one loop in UHF do not do much at 800 Mhz -
---He was talking about VHF circulators not being effective at preventing
800 Mhz energy from passing back down the TX line?
I've never heard of this before.
Ken
Take a tracking generator and sweep a Wacom 678 duplexer and look beyond
440 / 450 on up to 600 and beyond. If memory is correct a single cavity
will have less than 10 db attenuation at 800.
Ssb
Yahoo! Groups Links
* To visit your group on the web, go to:
At 12:34 PM 5/5/2004 -0500, you wrote:
Take a tracking generator and sweep a Wacom 678 duplexer and look beyond
440 / 450 on up to 600 and beyond. If memory is correct a single cavity
will have less than 10 db attenuation at 800.
---I said CIRCULATOR, not DUPLEXER :-)
Ken
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