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   Home   Help Search  
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Author Topic: Ideas for Law Enforcement unit  (Read 25977 times)
KG5FQT
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Posts: 14




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« Reply #15 on: February 19, 2015, 05:49:54 AM »

Jack, sent you a PM for some ideas, thx
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K6BBB
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Posts: 0




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« Reply #16 on: February 19, 2015, 11:50:21 AM »

. . . . If I have to replace the mount every year for the cable being pinched, its the cost I will have to handle.

Sorry, I zoned out on the 70cm band need.

If I was having to replace a damaged coax often and a mag mount was the only option, I would cut off the damaged cable leaving enough pigtail out of the mag mount to install a BNC, TNC or similar connector to attach replacement coax to. Not the best remedy, but it would save some $$. I don't know about a Tahoe's door, window or gasket system, but hopefully there is someplace to run the cable through without damage.

As Jack, W2OLZ notes, a black 19" whip and NMO mount is pretty hard to see and I think it's a stock item from Motorola.

Good luck!
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KG5FQT
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Posts: 14




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« Reply #17 on: February 19, 2015, 12:56:23 PM »

Call me naive, I'm not anticipating a pinch issue. The mag mount up there now is tucked away enough that when i recently inspected it, there are no pinch points at all and you cant tell where the door has been closing on it.
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K6BBB
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« Reply #18 on: February 19, 2015, 01:41:42 PM »

Call me naive, I'm not anticipating a pinch issue. The mag mount up there now is tucked away enough that when i recently inspected it, there are no pinch points at all and you cant tell where the door has been closing on it.

Excellent!
73
Rob
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KA4NMA
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Posts: 496




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« Reply #19 on: February 19, 2015, 08:51:37 PM »

If you want gain, go for the Larson 270B.  After using Comet and MFJ, I am well pleased with the Larson.  Remember basic physics and electronics.  Gain is a function of length.  Also check to see how gain is measured. If it says Db be wary.  Gain should be Dbi (ideal).  Gain is measured relative to something, so you need a standard.  Think of a vertical as half of the antenna and the car body (ground) as the other half.  Mag mounts do not provide a ground connection.

For all things mobile, check out Alan's website k0bg.com.  Another parameter to consider is power.  Best to come from the battery, and not a cigarette plug or other shortcuts.

Randy ka4nma
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K1DA
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Posts: 715




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« Reply #20 on: February 21, 2015, 08:20:06 AM »

See what Austin Custom Antenna can do for you.  They build multiband units for many different combos including broadcast FM  and VHF two way  on one stick and multiband scanner antennas. 
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W8JI
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Posts: 9749


WWW

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« Reply #21 on: February 25, 2015, 03:32:39 PM »

For a long time, several of the local SO cars and the dispatch center had Ham radios. So do a few of the local State boys.

Some people need to worry about more important things.

As for antenna gain, most antenna gain is a big false claim. The theoretical maximum gain of a **perfect** 5/8th wave is less than 2.8 dB over a 1/4 wave antenna. When flaws are added, like the too small roof area for a image plane and the matching coil losses, we are lucky if the 5/8th wave breaks even.

This is why many commercial big-company antennas like those from Motorola, not stuff from aftermarket suppliers, was 1/4 wave or 1/2 wave. That may have changed, but the 2.85 dB theoretical for a 5/8th wave only applies when the ground plane is flat, even with the base, and large enough to act like it is infinite. 

If it were me, especially if it was a rough service application, I'd just use a 1/4 wave.
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WA2OLZ
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Posts: 110




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« Reply #22 on: February 25, 2015, 04:51:36 PM »

For a long time, several of the local SO cars and the dispatch center had Ham radios. So do a few of the local State boys.

Some people need to worry about more important things.

As for antenna gain, most antenna gain is a big false claim. The theoretical maximum gain of a **perfect** 5/8th wave is less than 2.8 dB over a 1/4 wave antenna. When flaws are added, like the too small roof area for a image plane and the matching coil losses, we are lucky if the 5/8th wave breaks even.

This is why many commercial big-company antennas like those from Motorola, not stuff from aftermarket suppliers, was 1/4 wave or 1/2 wave. That may have changed, but the 2.85 dB theoretical for a 5/8th wave only applies when the ground plane is flat, even with the base, and large enough to act like it is infinite. 

If it were me, especially if it was a rough service application, I'd just use a 1/4 wave.

Like he said!
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DONMTEXAS
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Posts: 15




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« Reply #23 on: February 25, 2015, 10:12:48 PM »

If you are going to use a mag mount on a chase vehicle go with the largest diameter magnet you can find. If you hit 100+mph,and you will, you may find yourself dragging the antenna down the road. At those speeds the wind stress loading increases exponentially.
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KG5FQT
Member

Posts: 14




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« Reply #24 on: February 26, 2015, 12:32:32 AM »

I have about 7" in between the raised "ribs" on top of the Tahoe. So I'm probably goin with a 5" mag mount. The tri-magnet mag mount which of course would be the strongest, probably won't fit with the raised ribs because of the spacing. So I need the biggest nmo mount that would fit between the 7-7.5" spacing. Or uhf mount if need be. Still haven't really decided on antenna. I understand a 1/4 wave, but which one? Need something low profile when working normal days. Then switch to something a lil better like the  Comet CA-2x4SRNMO. But i do need a antenna that will handle the occasional high speed
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N7IBC
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Posts: 12




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« Reply #25 on: March 02, 2015, 02:31:13 PM »

I carry a mag mount with a Larsen dual band antenna in my patrol unit.
The radio is a Yaesu HT, (VX-6R) tucked in my gear bag.
I live in a very rural, high altitude valley in central Idaho, and our repeaters are up around 8,200 feet ASL.
Town is at 5,000 feet ASL.
I can pretty much hit them whenever I want, from everywhere I can go, while on patrol.

I have no room in my patrol vehicle for another mobile radio.
We operate on VHF and UHF, so the console is pretty full already.
I'm a 30 year LE officer, a 31 year ham operator, and the the senior patrol supervisor, so I don't really have time to get on the ham radio, on night shift.
If we have a weather event, (all the time in the winter), I will drag it out and hook it up, to listen to the ARES repeater.
In the summer, it's usually traffic related, a large forest fire, someone is lost, or a back country medical event has occurred.
Ham radio has, at times, played a vital role in emergency services, at least for me.
Having it available is not the issue, the real issue is making the administrators realize it does have "real, and actual" value to the community.
Unfortunately, in our area there have been some hams who try and hold themselves as, "lords of knowledge", and try to tell the LE experts how to operate their systems.
When that happens, a large smelly, stone wall is put up between the two organizations, with the public safety operators turning a deaf ear to any and all help.
Our local SAR group is coming around, slowly, and a few of their members have become licensed in the last year.
The worst possible thing I heard a ham tell a LE administrator was, "when your system fails, ours will work", or "you need to do this, or do that".
Again, deaf ear syndrome strikes.
What a lot of our local hams do not realize is that our primary, wide area coverage 2M machine is in the same public safety mountaintop site as our LE repeaters. If the LE system fails, well, ours does as well. Our VHF system has crashed at least three time this winter, due to severe weather events, so no one is immune.
I encourage any and all law enforcement officers to get heir ham radio license, and carry a radio with them, as many sets of eyes are better then just a few, and most hams I know are very good at reporting things they see.
But remember, the two systems serve the public, just from a different level.
 



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K3UG
Member

Posts: 9




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« Reply #26 on: March 11, 2015, 08:48:57 AM »

Not sure it is a wise idea to install ham gear in a public service car to use while you are being paid with public funds to work. It could create ethics issues. If you really want it I would use a HT and keep it low profile.

This would imply that no amateur could install a transceiver capable of transmitting on amateur radio frequemcies in a "company" vehicle. C'mon man.
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NC4TB
Member

Posts: 38




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« Reply #27 on: April 05, 2015, 04:48:05 PM »

I'd go with the biggest mag mount that would fit flat on your roof, then try to secure it in the opposite direction from the side the coax feeds from just as a little extra insurance against loss of your antenna "at speed", or if encountering a low hanging limb or wire. You could use some black braided nylon fishing line or similar.
    Ignore the nandering nabobs of negativity. As a deputy sheriff ten years ago I " found" a spot on the backside of a mountain that NONE of my duty radio frequencies would work simplex or repeater on any authorized nets, sheriff, police, EMS, or fire. And to top it off, this was one of the few areas where Verizon wouldn't work either. Fortunately, there was no emergency as I was  attempting to serve a civil paper and no one was home. But it could have been serious to have no comms.
    I am certain with my knowledge of the local repeaters, I could have easily accessed two or more 2 mtr repeaters with autodial capabilities, but I wasn't a ham then. Good luck!

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N7WR
Member

Posts: 110


WWW

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« Reply #28 on: April 17, 2015, 06:35:32 PM »

WW6BBB, thanks for the help, but I need a dual band antenna as my local repeaters are both 2m and 70cm . I didnt see a dual band on that page.

I was close to getting the Diamond NR-72BNMO, then read on HRO that its not recommended for magnet mount, ground plane required. Wish i could find a Larsen or Motorola Dual Band antenna, like KB4QAA suggested, but  under 20" , but cant seem to find one. So I am still at square 1, kinda leaning towards a Comet B-10 at this point.

Mag mounts are my only option, the way I swap new units, or borrow units, I need something readily transportable. My 700/800 mhz radio is using a mag mount because they didnt want anymore holes in roof, no way they will allow for ham. If I have to replace the mount every year for the cable being pinched, its the cost I will have to handle.

As far as radio shop, we really dont have one. We have been on a Motorola 800mhz system for at last 25+ years. It is serviced through the local Motorola service company. We were on VHF proceeding that, and those radios are long gone. The radio shop wouldn't answer a single question even if I asked, they only service Motorola 700/800 systems for us and wont venture out of that.

As far as the guys who say they know local law enforcement with hams, is there anyway of finding out if any are on Tahoe SUV's and what antenna system they are using?

As a fellow LEO I too operated a 2/440 from my assigned police vehicle over a period of many years.  For some of that time I did use the NR 72 BNMO on a mag mount and it worked just fine regardless of what the manufacturer says
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