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bbradburry(at)bellsouth.n
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 Posted: Sun Mar 17, 2013 8:03 am Post subject: Constant RX on a particular frequency |
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What are the probable causes if you are getting a constant loud SHHHHHHHHHH on a particular frequency and the radio is showing an RX? I can faintly make out a voice over the hiss from time to time, but I can not make out what is being said. Is this a stuck mike? Would breaking squelch cause this? I am trying to determine if this is caused by my radio or the transmitting radio. Also during this time, one other aircraft made a broadcast and it came in loud and clear and stopped the hiss while he was transmitting.
This is happening with the approach freq at my home airport. This has been going on for some time now. If I switch to the tower freq the problem resolves. The approach transmitter might be 15-20 miles further out. Yesterday, I mentioned the hiss to approach and she did something that made it better, then asked me if it helped.
Does anybody know what might be going on here?
Bill
[quote][b]
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berkut13(at)berkut13.com
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| Posted: Sun Mar 17, 2013 8:41 am Post subject: Constant RX on a particular frequency |
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Radio, antenna specs? Is this something new, or has it always done that? Have you changed the squelch settings?
From: Bill Bradburry (bbradburry(at)bellsouth.net)
Sent: Sunday, March 17, 2013 11:01 AM
To: aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)
Subject: Constant RX on a particular frequency
What are the probable causes if you are getting a constant loud SHHHHHHHHHH on a particular frequency and the radio is showing an RX? I can faintly make out a voice over the hiss from time to time, but I can not make out what is being said. Is this a stuck mike? Would breaking squelch cause this? I am trying to determine if this is caused by my radio or the transmitting radio. Also during this time, one other aircraft made a broadcast and it came in loud and clear and stopped the hiss while he was transmitting.
This is happening with the approach freq at my home airport. This has been going on for some time now. If I switch to the tower freq the problem resolves. The approach transmitter might be 15-20 miles further out. Yesterday, I mentioned the hiss to approach and she did something that made it better, then asked me if it helped.
Does anybody know what might be going on here?
Bill
[quote]
href="http://www.matronics.com/Navigator?AeroElectric-List">http://www.matronics.com/Navigator?AeroElectric-List
href="http://forums.matronics.com">http://forums.matronics.com
href="http://www.matronics.com/contribution">http://www.matronics.com/c
[b]
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billp(at)wwpc.com
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| Posted: Sun Mar 17, 2013 8:59 am Post subject: Constant RX on a particular frequency |
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No hints for us? Did she say what she did?
The constant SHHHHHH is the squelch set too loose or a very weak signal on that channel. This could be local noise (computer, laptop, PDA, electronic instruments all make a little RF noise) in your airplane of a mix of frequencies that makes a weak signal on that channel.
Adjusting the squelch setting higher will fix the problem. If it's a not so weak signal, adjusting the squelch to get rid of annoying signal may mean that you may not hear a call from a controller when you're right at the outer edge of coverage. It's a balance.
The squelch should be adjusted so that signals that are useable (ones you could make out what is being said) are let through and noise and signals that are distant or weak and just a distraction (i.e. others using the CTAF channel your local airport at another airport) are suppressed.
Bill
On 3/17/13 9:01 AM, Bill Bradburry wrote:
[quote]
What are the probable causes if you are getting a constant loud SHHHHHHHHHH on a particular frequency and the radio is showing an RX? I can faintly make out a voice over the hiss from time to time, but I can not make out what is being said. Is this a stuck mike? Would breaking squelch cause this? I am trying to determine if this is caused by my radio or the transmitting radio. Also during this time, one other aircraft made a broadcast and it came in loud and clear and stopped the hiss while he was transmitting.
This is happening with the approach freq at my home airport. This has been going on for some time now. If I switch to the tower freq the problem resolves. The approach transmitter might be 15-20 miles further out. Yesterday, I mentioned the hiss to approach and she did something that made it better, then asked me if it helped.
Does anybody know what might be going on here?
Bill
[b]
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nuckolls.bob(at)aeroelect
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| Posted: Sun Mar 17, 2013 9:09 am Post subject: Constant RX on a particular frequency |
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At 11:01 AM 3/17/2013, you wrote:
| Quote: | What are the probable causes if you are getting a constant loud SHHHHHHHHHH on a particular frequency and the radio is showing an RX? I can faintly make out a voice over the hiss from time to time, but I can not make out what is being said. Is this a stuck mike? Would breaking squelch cause this? I am trying to determine if this is caused by my radio or the transmitting radio. Also during this time, one other aircraft made a broadcast and it came in loud and clear and stopped the hiss while he was transmitting.
This is happening with the approach freq at my home airport. This has been going on for some time now. If I switch to the tower freq the problem resolves. The approach transmitter might be 15-20 miles further out. Yesterday, I mentioned the hiss to approach and she did something that made it better, then asked me if it helped.
Does anybody know what might be going on here? |
The potential sources for this phenomenon are
endless . . . but if folks on the ground can
do something that has an effect, then it sounds
like (1) they have some notion as to what is
happening even (2) if they don't know why it happens.
If the mystery signal is easily overpowered by
a transmission from an source with no mystery
attached suggests that it's not something that
is happening by design. A weak-signal anomaly.
ATC facilities tend to co-locate their assets.
There's a couple of sites west and SW of the
ICT that feature an equipment building surrounded
by a quad of towers.
[img]cid:.0[/img]
Each tower mounts LOTS of antennas with each antenna
intended to service one radio in a shared RF environement
with lots of other radios. Unfortunately, this environment
is akin to an orchestra of a few dozen instruments on which
each user is playing their own tune.
[img]cid:.1[/img]
Back in my two-way radio days we used to call sites like this
"intermod city" referring to the difficulties of co-locating
many radios. The signals from two talking radios could 'mix'
in adjacent, overloaded receiver circuits to product poor behavior in the
offended radio and in rare cases, RERADIATE products of that
attack with sufficient strength to be heard by a sensitive receiver
some distance away.
When your observations mentioned involvement of ATC facilities
the first image that popped to mind was an un-mitigated intermod
situation on the ground . . . one that the controllers have been
made aware of and are able to react in some manner that makes it
go away even if they cannot fix it. Conversely, it may be a condition
that's on a list of squawks waiting for the techno-wienies to come
out and fix it.
Just a guess . . .
Bob . . .
| Quote: |
Bill
No virus found in this message.
Checked by AVG - www.avg.com
03/17/13 |
Bob . . .
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n744bh(at)bellsouth.net
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| Posted: Sun Mar 17, 2013 10:15 am Post subject: Constant RX on a particular frequency |
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Here's a very remote possibility if the freq you're hearing this on is 134.825 or higher. That freq is the 5th harmonic of channel 1 on the citizens band and it would go up for each channel. Once I heard this happen on a center freq while flying at 35,000 and I forget which CB channel it was but he was 5x5. Of course it drove everybody on the freq nuts because we couldn't talk to the guy but we soon flew out of it. It could be that a CBer has a radio on with a stuck mike and doesn't know it. If the freq you're hearing this on is lower then you can discount this possibility.
Bill
[quote] ---
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nuckolls.bob(at)aeroelect
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| Posted: Sun Mar 17, 2013 12:39 pm Post subject: Constant RX on a particular frequency |
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At 01:14 PM 3/17/2013, you wrote:
| Quote: | | Here's a very remote possibility if the freq you're hearing this on is 134.825 or higher. That freq is the 5th harmonic of channel 1 on the citizens band and it would go up for each channel. Once I heard this happen on a center freq while flying at 35,000 and I forget which CB channel it was but he was 5x5. Of course it drove everybody on the freq nuts because we couldn't talk to the guy but we soon flew out of it. It could be that a CBer has a radio on with a stuck mike and doesn't know it. If the freq you're hearing this on is lower then you can discount this possibility. |
I wouldn't think that the ATC person would have been
able to 'make it better' but your hypothesis for a
potential interference source is sound.
While living in Wichita, I would occasionally hear
a cb'er yakking it up for just a few seconds as he
drove along a main street about 75 yards south of
my house. His transmitter was getting into the audio
system in my workshop. I think I know who it was at
least by sight of the vehicle. On several occasions
I saw a white van in the local parking lots that
sported a very hefty, center loaded antenna right
in the middle of the roof. The van didn't carry
ham tags and the antenna was not a multi-band HF
device. My assumption is that he had a really big-dog
linear amplifier on his CB transceiver.
Those products are not only STRONG on their fundamental
operating frequency, they can be rich in harmonic
content as well. Since they're illegal devices, the
folks who sell them are not strongly disposed to control
spurious emissions.
Bob . . . [quote][b]
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