RF spkr mics

[speedway_navigator]

Any of you guys (youse for my New Jersey friends) have any studies or spectrum analyzer screen shots showing the dB gain from a mic with an antenna versus audio only?
A PD I've worked with uses them even though the county has 5 sites, they say it is better than the antenna on the radio.
A Kenwood guy my buddy talked to said they had problems with users not getting the side connector properly seated which caused problems.

thanks

 

[Cameron314]

I saw a Motorola study on it a long time ago. I don't see them used often anymore. One issue would be that almost ever user I've ever seen using one has the cable across the back and over the shoulder with the mic upside down at a 45 with the antenna pointed down. No point to using one like that.

 

[hill]

Our local PD has newer style ones with antennas on the APX.

They have used antenna mics going all the way back to MTS2000 radio. Even with being a trunked radio systems the whole time on 800 MHz.

 

[RFI-EMI-GUY]

There indeed was a very good Motorola study decades ago. Even published in IEEE transactions. I would be afraid to refer to it these days since there has been so much development on portable antennas (some of it plain awful).

 

[speedway_navigator]

thanks, searching in progress

 

[prcguy]

Compared to a radio on a belt with the antenna up against a body, a speaker mic at head level with an antenna will put out a better signal, even with the extra length of small coax.

 

[speedway_navigator]

I've seen officers zip tie the extra length of cable to make a loop, bet a DTF would show a bump at that point. I bet it would be too hard to put an RF mic on a VNA with the radio specific connect variations between mfgs. A signal strength reading from a new one as a standard would be the only way I could see to test for coax attenuation.

 

[MTS2000des]

That's the caveat of the PSM (public safety microphone, is what MSI calls them)- the cord has to be relatively straight with no loops or sharp bends. Back in the Jedi days, they used to have a slip sheet showing the correct way to don and use a PSM and it specifically showed a red circle with a line through it with a zip tied cord.

We opted for standard RSMs and 5/8 wave antennas, which are what our drive testing and RFP called for spec wise. The PSM in theory should radiate better than a belt worn device, but only if the user routes the cable correctly, and PROPER PSM antenna is used.

 

[buddrousa]

When I was on the Department and we were still Motorola Type 2 800 I had a Speaker Mic with the Antenna on it and I can say 1st hand I could talk in places where others could not hit the system using just regular Mics. That prompted some to remove their Mics or buy the Speaker Mics with the antennas on them.

 

[speedway_navigator]

I wonder multi band and or GPS radios have made it hard for PSMs to function now.

 

[mmckenna]

I wonder multi band and or GPS radios have made it hard for PSMs to function now.

Our Harris XL-200's have the antenna connection for the PSM's. We do not use them, though. I cannot imagine walking around with that 'big ten inch" antenna on your shoulder.

Considering many public safety systems are designed from the ground up for on street coverage with the radio on the belt, it's probably not necessary for most. I know I haven't seen one in use locally in a very long time.

The Harris branded ones are pretty expensive, too. I think the list price was $300 or so. That gets kind of expensive when most speaker mics are pretty much an expendable accessory. Having to replace those frequently would get to be an expensive bother.

 

[K3JCT]

The IEEE study can be purchased here: https://ieeexplore.ieee.org/abstract/document/108386
The TIA 329.3 document can be purchased here: https://standards.globalspec.com/std/14608351/tia-329-3-a
The IEEE study is from 1991. The TIA 329.3 document looks to be relatively new.
Hope this helps.

 

[wa8pyr]

Compared to a radio on a belt with the antenna up against a body, a speaker mic at head level with an antenna will put out a better signal, even with the extra length of small coax.

Ditto. The issue isn’t really gain, more like elevation. That extra 18” or so can make a big difference, especially if the user keeps the antenna pointed up so it’s clear of their shoulder.

One caveat is to keep an antenna on the radio as well as the speaker mike, if your equipment allows it. We had a couple of times where an officer got into a scuffle, and their speaker mike was yanked off the radio; fortunately there was still an antenna on the radio.