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  #1 (permalink)  
Old 02-05-2013, 9:50 PM
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Default 39.4 MHz CHP interference?

I get intermittent, and very annoying, buzzing and humming on CHP 39.4 frequency. This occurs on all my Motorola radios, as well as my scanners. On my scanners, the interference is basically full signal. It makes monitoring that channel very difficult.

This interference persists at my home, and anywhere I drive, both on handhelds and mobiles. Anyone know what this is?

Paul
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Old 02-05-2013, 10:31 PM
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Quote:
Originally Posted by Anderegg View Post
I get intermittent, and very annoying, buzzing and humming on CHP 39.4 frequency. This occurs on all my Motorola radios, as well as my scanners. On my scanners, the interference is basically full signal. It makes monitoring that channel very difficult.

This interference persists at my home, and anywhere I drive, both on handhelds and mobiles. Anyone know what this is?

Paul
Do you get that signal with the correct pl for your area ? .?
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Old 02-05-2013, 10:39 PM
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I don't know if I would call it a "signal", but no, not with a PL. The strange thing is on my scanners, it sounds broken and staticy, but shows full signal. Almost sounds like electrical interference or "birdies", but on so many different receivers and locations, I am baffled.

Paul
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Old 02-05-2013, 10:49 PM
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On a side note.......I just installed a low band Maxtrac in my car in San Diego, and I can pick up Santa Fe Springs CHP (83) 150 miles away using a 1/4 wave VHF HIGH antenna!

Paul
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Old 02-05-2013, 11:48 PM
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It is very likely some electrical interference, common on low band VHF. This is one benefit of programming CTCSS as the squelch won't break unless the proper tone is present.
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Old 02-06-2013, 1:57 AM
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Originally Posted by Anderegg View Post
On a side note.......I just installed a low band Maxtrac in my car in San Diego, and I can pick up Santa Fe Springs CHP (83) 150 miles away using a 1/4 wave VHF HIGH antenna!

Paul
OK, I gotta ask cuz I'm confused. I thought Maxtrac was a vehicle suspension. So what's that got to do with low band (you said "low band Maxtrac")? Does the suspension help with reception? How does that work? Or is there something else called Maxtrac that has something to do with radio reception? The antenna part I understand, although it's interesting to get good low band reception on a high band antenna. Anyway, I'm just askin' cuz I don't get it...
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Old 02-06-2013, 2:38 AM
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Do a google search for "Maxtrac".....the first 11,800,000 hits or so should clear things up. :-P

Paul
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Old 02-06-2013, 3:07 AM
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Do a google search for "Maxtrac".....the first 11,800,000 hits or so should clear things up. :-P

Paul
Actually, I did that before posting. I got 354,000 results like:

Maxtrac Suspension
maxtracsuspension.com/
Maxtrac Suspension manufactures all three suspension solutions for your vehicle, whether lifting your truck 6", leveling it out for slightly beefier tires, or lowering ...

Maxtrac Suspension | Facebook
www.facebook.com/maxtrac
Maxtrac Suspension. 9579 likes 355 talking about this.

Maxtrac suspension sold by AM | AutoModified
automodified.co.za › AutoModified Shop
Sep 27, 2012 – MAXTRAC suspension being advertised in our beloved Speed and Sound Magazine. Well now you can buy the MAXTRAC Coilover ...

MaxTrac Suspension (MaxTrac) on Twitter
https://twitter.com/MaxTrac
MaxTrac Suspension. @MaxTrac. Providing all 3 suspension solutions for your truck or SUV, lowering / lifting / leveling and the most competitive prices in the ...

Maxtrac Suspension - Anaheim, CA
www.yelp.com › Automotive › Auto Parts & Supplies
Rating: 5 - 1 review
1 Review of Maxtrac Suspension "Maxtrac makes some of the nicest lifting


etc.

Maybe Google works differently for you than it does for me.

Last edited by oracavon; 02-06-2013 at 3:12 AM..
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Old 02-06-2013, 4:28 AM
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A Maxtrac in this context is a Motorola mobile-mount radio...available in several band and channel configurations up to 32 channels. It is older technology that is not narrowband compliant, but it IS a bulletproof radio system. Since lowband is exempt from the narrowband requirements, it is a very functional option for someone needing a no-frills lowband radio.

I also have a Lowband Maxtrac (32ch) in my truck, and it still works very well

And in response to the OP's original query: My Maxtrac is a 42-50 mhz model, so I cannot program in any of the new 39mhz CHP channels. I do have the other CHP freqs in the radio, and I get occasional interference on several channels. I consider that to be "nature of the beast" on lowband frequencies, and just let the CTCSS filter it out...I never even know its happening unless I see the red LED flashing.
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Old 02-06-2013, 6:16 AM
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Bluetooth has a tendency to interfere with the lowband and UHF frequencies I have (Only thing left in the low band range in my part of the country is CB and the occasional road department) very similar to what you are describing, open carrier with slight "popcorn" static. CAT5 interferes with everything especially VHF.
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Old 02-06-2013, 10:30 PM
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Quote:
Originally Posted by gmclam View Post
It is very likely some electrical interference, common on low band VHF. This is one benefit of programming CTCSS as the squelch won't break unless the proper tone is present.
Exactly.... My point exactly.
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Old 02-06-2013, 10:34 PM
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Quote:
Originally Posted by duster View Post
A Maxtrac in this context is a Motorola mobile-mount radio...available in several band and channel configurations up to 32 channels. It is older technology that is not narrowband compliant, but it IS a bulletproof radio system. Since lowband is exempt from the narrowband requirements, it is a very functional option for someone needing a no-frills lowband radio.

I also have a Lowband Maxtrac (32ch) in my truck, and it still works very well

And in response to the OP's original query: My Maxtrac is a 42-50 mhz model, so I cannot program in any of the new 39mhz CHP channels. I do have the other CHP freqs in the radio, and I get occasional interference on several channels. I consider that to be "nature of the beast" on lowband frequencies, and just let the CTCSS filter it out...I never even know its happening unless I see the red LED flashing.
I'm sure you can get it modified for 39 MHz. .
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Old 02-07-2013, 7:35 PM
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Quote:
Originally Posted by gmclam View Post
It is very likely some electrical interference, common on low band VHF. This is one benefit of programming CTCSS as the squelch won't break unless the proper tone is present.

Quote:
Originally Posted by scottyhetzel View Post
Exactly.... My point exactly.
But that doesn't always solve the problem. I have a similar problem on 39.44 and 39.36 - constant noise on those frequencies, with multiple radios and antennas. As you say, the squelch won't open until it gets the right PL, but that doesn't stop the noise from interfering with signal reception once the squelch opens. In my case, it can be so bad the the desired signal is virtually unlistenable.
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Old 02-08-2013, 4:20 AM
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Well, if it's following you around and present on many different radios including professional rigs, then I am inclined to think it might be caused by some other device you are using that you keep on you all the time (that is if we go on the assumption that it is not a widespread problem common to the whole area you cover). If it follows you while walking away from your car and using a portable radio then maybe it's some portable smart phone, tablet, or digital camera?

Try using one portable receiver and walking around with absolutely no other electronic device on your person in various areas and see if the noise decreases or ceases completely. If so, then go back and add one electronic device that you normally carry at a time to test when the problem recurs. You might find which device you use frequently is causing the problem.

I think you have stated in other threads that you are a news photographer or stringer or some such. If so, it could even be your professional photography or videography gear. Even things like portable lights, motorized zoom lenses, etc., might be spewing out lots of garbage that kills local RF, especially low band. Even when they are supposed to be "turned off" some internal smarts, say in your super fancy high level professional quality DSLR or even in your quicky backup point and shoot might remain on at some level and spew out enough RF hash to cause issues on your equipment.

Something else you could try is to sniff your equipment with a portable scanner held up close to each piece of gear to see which one causes the most hash. If possible, use AM mode to do this and turn the squelch completely down/off. Start with the antenna on and then remove it so that you have to be very close to the offending device to get the garbage so that you can zero in on the exact piece of gear. Of course, it could be coming from multiple devices so be ready for that too.

The reason you see the full scale S meter reading on your scanners but only hear the audio of the noise intermittently is that the squelch circuit is based on FM background noise (the hash you hear when the squelch is turned completely down under normal no interference situations). Many forms of electrical interference are broadband in nature relative to the receiver's specialized internal filtering. What gets through to the squelch circuit just looks like more of the same regular FM background noise so it gets muted. The S meter, however, is looking at different circuitry and actually looking at signal levels present within the final IF filter passband. So in FM mode the meter might show the presence of a signal but the squelch is still muting the audio. Since the noise from the interference is varying in quality, possibly including varying its bandwidth and has random phase, frequency, and amplitude changes there will be times that the interference alters enough to make noise like an actual FM (albeit distorted and low quality FM) signal so that the audio circuit unmutes and you hear the noise. Many types of digital gunk from computers, networking equipment, smart phones, cameras, etc., will radiate quite well and through quite a range of radio frequencies; they will often change in some way as the internal systems go through their regular digital routines.

That is why I suggested using the AM mode to sniff for the culprit(s). AM is much more prone to external noise so you will usually hear it better while in that mode.

-Mike
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Old 02-08-2013, 7:43 PM
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The weird thing is that I get this on a Motorola low band handheld as well......which prompted me to wave the rubber duck antenna around like a wand to try to sniff out the source of the interference. Upon further testing, the interference goes away when I remove the antenna, but does not change when I wave the radio around.....very strange. Right now I have the handheld turned on, and no interference. I know when it it picking up the "signal", because the red light on top will start blinking.

Next time it happens I will record a video and slap it on YouTube.

Paul
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Old 02-15-2013, 9:52 PM
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The 42-50 split Maxtrac or Radius should be able to RX even down to 39 mhz.
You likely will have to adjust the VCO coil slug to get the "steering line" voltage to be just under 2 volts on your lowest frequency so the VCO locks.
It sounds more difficult than it is. And I find I get decent RX for about 10 mhz
And you might not get full sensitivity, but I find they are pretty useable.
I have one on the bench this very minute that is just a few dB worse RX at 39.5 than it is at 47 mhz.
Since "local" noise is often the limiting factor, having a low band RX that is off a few dB of sensitivity compared to the best channel, is not really that bad.
Better than not being able to to hear that channel at all.
And if you want to improve the sensitivity just a little, you can stuff a "slug" of 12 GA copper wire in a coil or two of the RX front end and make plenty of improvement.
Why not try it?
Enter the 39.XX00 freq using the shift keys in the Maxtrac RSS program.
For example 39.46000 would look like #(.$^)))
Un-shift for the period and fill all the zeros.
You might be surprised.
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Old 02-15-2013, 9:57 PM
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So in my 36-42 MHz Maxtrac, if I do the shift thing, I can shove in 42.34 MHz? That would be useful.

Paul
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Old 02-15-2013, 10:42 PM
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Yes.
And you likely can get up to 45 mhz. Certainly should work for all the 42 mhz channels.
I would not try it on TX without checking with a service monitor, but it should RX a couple mhz above or below the the design split.
If you need to go too high or too low, then you start "trading" VCO lock above for below, and vice versa.
I have done lots of 42-50 radios, and usually you get that 10 mhz wide of usable RX.
My best guess is that the lower split the radio, the narrower that usable "bandwidth".
Motorola only specs 8 mhz on the 42-50, 6 on the 36-42 and 6.3 on the 29.7 to 36.
But in my experience you can get a couple usable mhz more on all of them.
Some below the split and some above.
Especially if you just want RX.
VERY hard to beat the trusty Maxtrac.
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Old 03-27-2013, 12:22 AM
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Wow, I just came across this thread in my quest for a really sensitive dedicated low-band scanner.

Does the Maxtrac "scan" like a scanner, or do you have to manually change channels on it?
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Old 03-27-2013, 12:35 AM
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My research indicates that it's a 2-way radio that scans, but only when the mic is on the mic clip, per this thread:

Maxtrac: How do I use scan?

There are a few for sale on eBay if you want to see what they look like.
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