Maxtrac birdie on 161.07 - workaround?

[sataraid1]

Is there a workaround for the 161.070 birdie on Maxtrac radios? I've seen numerous references to this, but no mention of a fix.

I'm also unclear if this is the result of a defect, or if it's unavoidable due to the nature of the radio. I've read conflicting information regarding this.

Can someone set me straight? 161.07 is a must-have frequency, if I can't use it with this radio it's essentially useless to me, which is a shame because it's an absolutely mint radio.

Is there an adjustment that can made to move the interference to an adjacent but unused frequency?

I'm trying to find out what I can before I even consider asking at the shop. It needs to go back because of a programming error, but if there's a fix I'm going to have to tell them specifically what to do ... otherwise I'm afraid they'll charge me another $50 just to look at it and say "eh, we can't fix that".

Thanks in advance.

[sataraid1]

If there's no workaround, can anyone actually shed more light on the issue? Is this birdie particular to models of a certain configuration? A specific production run?

I have found GM300 literature that lists 161.070 as a "self quieting frequency that is not available", but haven't found anything in black and white that ties it to the Maxtracs.

[n7maq]

If there's no workaround, can anyone actually shed more light on the issue? Is this birdie particular to models of a certain configuration? A specific production run?

I have found GM300 literature that lists 161.070 as a "self quieting frequency that is not available", but haven't found anything in black and white that ties it to the Maxtracs.

Try a search here on the board (search just 161.070), this is not a new problem and it has been talked about in the past.


Jim

[sataraid1]

Try a search here on the board (search just 161.070), this is not a new problem and it has been talked about in the past.

I did search, and found references to the problem existing, but no workarounds or explanations as to why some Maxtracs and GM300s seem immune even though it's a documented issue with the radios.

There has to be a rhyme and a reason, but without knowing what it is, anyone who buys a Maxtrac for railroad monitoring on AAR 64 is just gambling. I'm hoping documentation will surface that links the issue to a particular feature set or production run.

[n7maq]

http://batboard.batlabs.com/viewtopic.p ... it=161.070

You will not be able to get rid of it 100%, but there are some ideas on ways to reduce it to a useable level.

Jim

[Bill_G]

Tightening screws and improving grounds reduces birdies - who knew?

Have you measured how bad you're getting hit on 070?

Nevermind - just re-read the thread and you are paying someone else to fix it. So, have you experienced the problem in this radio, or is it something you heard about, and are concerned it might happen?

[sataraid1]

http://batboard.batlabs.com/viewtopic.p ... it=161.070

You will not be able to get rid of it 100%, but there are some ideas on ways to reduce it to a useable level.

I read the thread mentioned above, but the suggestions were inconclusive, and the person with the problem just ended up buying a different radio, so I don't know that any of the fixes mentioned will work. I can open it up and give it a look, but given my mediocre skills, and the excellent condition of the radio I'm a little hesitant. Hacking around on some dirty old tech special might be a different story ...

Have you measured how bad you're getting hit on 070?

Nevermind - just re-read the thread and you are paying someone else to fix it. So, have you experienced the problem in this radio, or is it something you heard about, and are concerned it might happen?

I'm definitely experiencing the problem ... it's so severe on the channel in question that the radio won't scan. I just get noise. It does it with or without the antenna connected. I noticed that when the radio is powered up while on 161.070, for a couple of seconds there is silence, then the interference fades in over the course of about two seconds.

If I could just get it to the point where the interference was below the squelch threshold and the unit would scan, I could live with it.

[Satelite]

Hello:
Is the radio in qestion setup as a base or is it installed in a vehicle ?
I have had issues with certain freqs doe to the vehicles computer controller.
You may have to change the reference crystal to attempt to get around the birdie.
Works sometimes and other times it doesnt.
Ford pickups seem to be my worst offender when it comes to vhf .
Satelite

[Bill_G]

I'm definitely experiencing the problem ... it's so severe on the channel in question that the radio won't scan. I just get noise. It does it with or without the antenna connected. I noticed that when the radio is powered up while on 161.070, for a couple of seconds there is silence, then the interference fades in over the course of about two seconds.

If I could just get it to the point where the interference was below the squelch threshold and the unit would scan, I could live with it.

Have you popped the covers and tightened the sqeulch? There should be a pot on the rf board between the detector chip and 14 pin board interconnect marked SQ next to it on the board. If that helps, then you should go through the process of tightening all the board screws as discussed in the other thread. If you are comfortable with it, remove the board and clean the pins of the interconnect if your shop hasn't done it already.

[sataraid1]

Have you popped the covers and tightened the sqeulch? There should be a pot on the rf board between the detector chip and 14 pin board interconnect marked SQ next to it on the board. If that helps, then you should go through the process of tightening all the board screws as discussed in the other thread. If you are comfortable with it, remove the board and clean the pins of the interconnect if your shop hasn't done it already.

Well, I took the unit apart this weekend, and aside from one very small mummified spider, I found that the inside was just as clean as the outside.

I took out both boards, cleaned the interconnect very well, reseated both boards and tightened everything down. No change.

I took the radio to the truck, and hooked it to the antenna, then found the squelch pot and turned it up until the 161.070 would scan. Unfortunately, the result was that far too much of my distant reception was lost, which kind of defeated the whole purpose in getting the radio.

Once I got it back on the bench, I adjusted the squelch back to "normal" and stepped through the channels. I was dismayed to find that at a squelch setting suitable for all the other channels, the interference was actually bleeding over on the two channels on either side of 161.070 (161.055 - AAR 63, and 161.085 - AAR 65). So I tightened it back up to the point where everything but 161.070 would scan and sealed it back up.

This sure seems like a confusing issue. No one has come right out and said my radio is defective, but no one has cited the Motorola literature stating that 161.070 is clearly prone to problems in radios of this vintage.

It's a shame, because other than the issue with the birdie, I'm quite impressed with the radio. I find it to be virtually as sensitive as my Icom out in the country, but impervious to the intermod that slays it in the city. I also really like having the ability to set up a scan list for each channel. Being able to have what amounts to 32 memory banks instead of 10 or less is great.

Sigh. It's always something. But I appreciate the help so far and any more that anyone might have to offer.

[PETNRDX]

It is actually a surprise to me that this doesn't come up that often involving pretty much any synthesized radios.
The Maxtrac ( and the similar GM300 line ) have four oscillators running...
7.776
45.1
44.645
14.4
And it is actually possible for a radio to "hear" its own birdies at any combination of those frequencies if they are strong enuf.
PY5FT gave the explanation of this combination on 05 Sept 05.
With all the frequencies these babies can be programmed to, I am surprised this doesn't happen all the time that someone finds a freq that won't work.
I pulled one GM300 and five Maxtracs off the shelf, and programmed them to 161.07.
Two of the Maxtracs heard the birdie bad enuf, that I doubt it could be squelched.
One just barely heard it, one enuf to squelch it, one not at all.
The GM didn't hear it at all either.
Likely just a case of how rich in harmonics the oscillator and the prescaler are, and how sensitive that particular RX is.
All the radios I tried are very clean inside because I have done a complete clean/PM/alignment on them.
So, it doesn't appear to me to be something that is "fixed".
More likely it is just something that an individual radio might do.
Maybe trade your radio to someone that has one you can actually test on the freqs of interest.
Or get another radio that has a different oscillator combination.

[sataraid1]

Thanks for the additional information regarding this bugaboo. It's nice to know, at least, that it's not my imagination.

Since it's looking like there's no workaround, the idea of a trade sounds nice, if I could get someone to program it for me well. I got a very good price on this radio, especially considering how mint it is. The programming cost brought it up to "reasonable". But paying to program another one would make it a pretty expensive 15 year old radio.

If it were some obscure channel outside my area, I'd just shrug my shoulders and forget about it ... but of all the frequencies for it to choke on, it had to be the one they use right in my backyard.

[Bill_G]

You could always loosen one of your spark plug wires. Should cover it right up.

[sataraid1]

Actually a better thought occurred to me ...

Is the hardware that causes the birdie on the RF board, or the logic board?

If it's on the RF board, wouldn't I be able to simply swap RF boards with someone who has one that's "good" on 161.07 and retain all my programming?

[PETNRDX]

I would think that to be kind of hit or miss.
Might work, might not.
I don't think it is worth trying.
And you would have to re-align the radio as the RF board and logic board settings would be different on two boards.
Takes way longer than programming.

[Bill_G]

Since the channel is important to you, and the problem is well known within the model, you should change models. CDM's have excellent rcvrs, and the one I have doesn't have this birdie.

[sataraid1]

Thanks again for the responses and the information. I do appreciate it.

It's a shame that after waiting so long to finally buy one of these, I ended up one that can't behave itself. If nothing else, perhaps my discussions on this and other boards will warn anyone considering a Maxtrac/GM300 for railroad monitoring to test units first or make sure they have a return option.

I think at this point I'll just stop flogging this horse and sell or trade the radio as-is, or repurpose it for something that doesn't require the channel.

[Satelite]

Hello
You wouldnt by chance have the 12.5 Khz model rather than the 25 Khz that the 161.07 is having issues with ?
What is the entire model number of the GM300 in qestion ?
Thank you
Satelite

[sataraid1]

You wouldnt by chance have the 12.5 Khz model rather than the 25 Khz that the 161.07 is having issues with ?
What is the entire model number of the GM300 in qestion ?

Actually, the radio in question is a Maxtrac ... but I've cited the GM300s in this case because I've found Motorola documentation stating that the GM300s shouldn't use the frequency.

However ... Here's a puzzler for you all ...

I have an I.C.E. active splitter that delivers about 3-4dB gain. When I hooked it to the Maxtrac, the birdie disappeared and 161.07 started scanning. Unplug the splitter, the birdie comes back. Plug it in again, the noise drops below the squelch threshold and it resumes scanning. I realize the answer may go over my head, but I'd be interested in knowing why that works.

But the good news is: this means the MaxTrac is quite usable for me now. Even if the birdie adds some noise to the occasional weak signal, I can live with that.

[Bill_G]

It prolly means your rcvr ant port is not properly terminated.

[sataraid1]

It prolly means your rcvr ant port is not properly terminated.

Is that something that can be fixed?

[Bill_G]

Sure. Try this - put a 50 ohm load on the ant conn and tell us if the birdie goes away.

[AEC]

There are times when the mixer in the 'Tracs are not in cans, but sealed under white silicone, you may want to look at that and fab a cover for the mixer.
Mixers radiate a lot of noise, and not being in a 'can', may help the annoyance propogate through the front end.

Shielding is always worth a try..