HT 1250 lapel mics

[GUNUT]

Hello,

I have a situation that does not seem to get any better, it involves Motorola HT 1250 portables.

Here are the details:

1 the freq band is 150 MHZ

2 have 3 Astro tac receivers all which are in the specs as far as their sens. and the antennas look good as far as SWR.

3 these are part of a voting system that uses a SNV 12 voter, which appears to be voting right, levels set per book.

4 when the officers call in they are complaing that they sound scratchy, like weak sig.

5 when I have the officers take off the lapel mics, ones without antenna just standard, they sound good, just like th body is desensing the RF along with the Kevlar vest.

6 I called Motot about the lapel mic issue but they have no record anywhere of this happening, even though you can see it happen with a spectrum analyzer.

7 they want to use the lapel mics but without more tac receivers, I cannot make it work well, only without the lapel mics. The lapel mics with the antenna on top are too long and do not work well.I know other places use lapel mics, but maybe it is 450-800 MHZ and not as funny about the human body/ vest arraingment.

Any body else have this problems with the lapel mics sucking?

Thanks

 

[SCPD]

Away from the body

Hello,

4 when the officers call in they are complaing that they sound scratchy, like weak sig.

5 when I have the officers take off the lapel mics, ones without antenna just standard, they sound good, just like th body is desensing the RF along with the Kevlar vest.

Any body else have this problems with the lapel mics sucking?

Thanks

You don't say if you tried to hold the radio away from the body with the mike still on, and talk thru the mike, and see if it's scratchy. The human body is a great attenuator when the antenna is laying on it.

I want to mention 1 thing I do with "scratchy" mikes. I take a fridge magnet, lay it magnet size up on the bench, and bang the mike into it. You will be suprised just how much junk will get attracted by the magnet, and how much that will clear up the audio. I do it with the radio itself too.

And you and another tech need to try and replicate the complaint yourselves, not just going by what the officers are telling you. When I get a radio back with some sort of complaint about it, the first thing I do is just use it myself for a couple of weeks, and majority of the time, there's nothing wrong with it. RF is funny, especially at 450 and beyond. All it takes is one bad spot, and they will tell you the radio is no good.

 

[CCHLLM]

The speaker/mics w/antenna were designed and promoted for UHF, and as many years as I was in the business, I don't recall ever seeing any MotherMoto service literature anointing the use of those on VHF. We did sell them for VHF use from time to time as long as the customer understood there was no guarantee that it would perform like a UHF model.

Other than the bench test connection provisions, which are actually designed for a proper 50 ohm bench test load, the radio really has no internal or external provisions for a user RF connection the way the models do that were designed with a speaker/mic and antenna combo to begin with.

The changing near-object conditions that a speaker/mic/antenna combo sees in everyday use won't maintain a decent SWR match anyway, and the way the speaker/mic antenna's RF couples to the radio through the bench connection provision is less than ideal to begin with. The SWR is OK but not great on UHF and probably horrific on VHF.

Due to an approximately three times wavelength ratio with VHF vs UHF, VHF near-object influence is approximately three times greater at a given object distance than UHF, so expect the VHF to be far more affected by close proximity to something. It's not really that simple due to reactivity characteristic differences between differing wavelengths, but the ratio is a fair rule of little finger if not thumb.

 

[GUNUT]

1250 lapel mic

Thank you thus far for you responses. Her is some further info:

1. The lapel mics that are being used do not use the external antennas, just the mic, so the atten.does come into play alot because now the radio is at the side and sometimes under the vest.Plus they have some officers who are using the stubby antennas that were meant to be on the mics.And my experience has taught me that the stubby antennas are even worse at 150 MHZ.

2. I did most of the testing with the radio away from the body and other times next to and other times just outside the truck. My sigs were 10-2 and I really believe that the problem is the radio next to the body.Now why the mics work ok,according to my biggest opponent on the dept. and the guy spearheading this,is probably the lay of the land and a smaller geographic area.Talking to this particular cop who knows enough to be dangerous is like talking to a brick wall,for every thing I show him, he has a yea but.....The good thing is that the Chief is on my side and understands and has personally observed this problem out in the field.He has even told an officer to take off his lapel mic and try again. Guess whta happens.........IT WORKS.

Thank you

 

[davidgcet]

the biggest part of it is the fact that when they remove the mic and hold the radio up to talk they have the antenna higher AND clear of their bodies. the effect will be more noticable at distance from teh nearest RX site. VHF has the advantage of longer range comms in open territory, but this is one of it's major drawbacks as far as portable use.

 

[GUNUT]

1250 mic

Yea, the dead giveaway is raising the radio to the face AND IT WORKS, the problem is that Motorola has "never heard of this problem" and since the cust. next door works, they think it should be the same even though the "other" cust. is a geographically different area ie. no dips and valleys, mainly flat.

 

[ramal121]

Any body else have this problems with the lapel mics sucking?

Thanks

A few years ago, complaints like this were rampant with VHF HT1250's and speaker mics. Motorola claimed there were no engineering probs, but the complaints persisted. I had one department that junked theirs and went back to HT1000's. No answers to you, but you are not alone....

 

[davidgcet]

clarify something for me, are these public safety mics that have the antenna jack on them? if so, you MUST use the antenna on the mic. just the act of plugging the mic to the side of the radio disconnects the radio's built in antenna port.

 

[CCHLLM]

I shoulda read it a little better, huh? OK, standard speaker/mics. Even those are not without their flaws. The coiled cord is practically always too near the antenna, and that alone will affect the radiating properties of those antennas more than you would believe until you test the theory and see that it's not a theory, it's a cold reality.

But I have another question: are these radios equipped with the older tapered pointy style of antenna with no ball or tip in their design? If so, those antennas were more some sort of crude RF termination device rather than a real antenna. Anything with the correct thread will work better than those pieces of junk. They're even annoying looking......

A new style antenna which looks like the old MT1000 antenna makes a big difference - it actually works. Anyway, as posted, the antenna against the body, bound up in a vest, officer sitting inside a car, up against all that belt hardware....... hey, stick with me here; I'm presenting a worst case scenario. With all the kinds of crap that can affect a VHF antenna through proximal object problems, it's a wonder any VHF radio works from the belt.

 

[W2NJS]

Congratulations to all, as this thread just gets seems to get more and more confusing with each post. First of all, PS spkr/mics (that means the unit has an antenna connection) don't have coiled cords and that's because the coax runs within the cable and would act an inductor if the cable were coiled. Second, Motorola has never recommended the use of a PS spkr/mic on VHF for the reasons cited in one post above. Third, if you connect the spkr/mic to the radio and don't put an antenna on the spkr/mic you're probably transmitting into an open antenna line that is not terminated. Perhaps the OP would wish to restate the exact setup he's facing so that the various points where problems might exist can be investigated and eliminated, one thing at a time the way troubleshooting is properly done.