How bad, cutting coax off a lowband antenna.....

[Brentd2183]

The officers on my department finally got mobile radios, we are lowband, 33.06, and they decided they wanted to install them on their own. Fair enough, i said bring them up the station when your done so i can tune them. Well half of them cut the coax at the radio, so they chopped about 10 feet or so on most. Then to add to things, one of them heard me talking about cutting down the whip to length. Well he goes up to the cheif's truck, and measures that antenna whip length and goes and cuts everyone elses antenna to that length, mind you these are two different brands! So he lops 6 inches off of them.
I've only gotten the meter on one of the 6 inch felons, these are 60watts radios and i was getting reading of like 150watts reflected and maybe 50 out, really really weird stuff. Now the PL259 that come with it, that was fun, they are the solder on types, they just stripped it and wrapped the inner conductor around the tip and shoved it in. Now i tried to talk sense to them, radio sense, i used big words like SWR and they all go hey, the dispatcher hears me so it must work fine.... I've just given up, eventually things will gett to toasted and burn something somewhere in the radio.
So how bad is this for everything, as bad as it is in my mind? Or this gonna get by ok. Thanks guys
Brent

[batdude]

stupid is as stupid does


or something like that anyway





doug

[mancow]

Finally got mobile radios........


WTF?


Personal mobiles for their own cars, is that what you mean?


As for the issue of the radios, if they won't listen to logic then what can you do?

It's their money and safety.


mancow

[Brentd2183]

Yes, as in they got mobile radios. The officer of the FD were issued portables but in our town with lowband we get huge dead spots and the portables are almost useless. So the dept finally bought 6 mobile radios for them in their trucks. They all did well enough i guess with putting them in and all, its just the stuff you cant see, or that extra radio knowledge they dont have, and we all know the looks people get on their faces the moment you start talking radio tech to someone, and you tell them you need a new mount and wipe.

[Tom in D.C.]

I know that "look." Their eyes just glaze over as they look away, and you might as well be speaking Chinese.

However, I have to wonder why your agency would buy six radios and not have installation included in the price, especially given the fact that it's a life safety system (same comment would apply to a PD). Might there be something in NFPA that requires a more formalized/controlled method of installing radios in vehicles? They have something about everything else, including backup repeaters and the like.

Perhaps your chief, if he/she understood the issues, could make a point of getting the work done right before someone gets killed.

[nmfire10]

Your new radios are likely to fry at this rate. I would have the antennas redone by you or at least someone who knows what they are doing. I have a Lt in my dept who is a wiring nightmare. I am about to disconnect his mobile radio when he isn't looking and remove it so it doesn't get fried. It's all screwed up.

[KitN1MCC]

god i know what u mean

one of the Customers has had radio for a while who he purchased years ago from a place that never even got the linsenced (SP) or anything

so i got him all legal. reprogrammed his radio to his new channel and Tuned all the Antenna. and he was ammazed how good the radio work now

and this is on VHF high too


plus at 33 mhz they need to tune then right damn morons

[Max-trac]

Since you are involved, you really need to document all of this in a letter of some kind to the highest level.

At the least the RF floating around is gonna screw up some other equipment, or fry the finals.

At the worst it will fail when someones LIFE depends on it, and they will sue EVERYBODY involved in the littlest way.

I can't believe in this day and age any agency letting this happen.
Maybe suggest they bid the work out to several shops and wash your hands of it.
It would be like letting everyone work on their own PCs.....

[SlimBob]

Now i tried to talk sense to them, radio sense, i used big words like SWR and they all go hey, the dispatcher hears me so it must work fine.... I've just given up, eventually things will gett to toasted and burn something somewhere in the radio.

a friend of mine had conversation about that with a co-worker. "I reckon that's why we're radio engineers and they are law enforcement."

[rickbuckner]

You're dealing with the customer not the equipment. Two different animals. You know what it takes to fix the radios and in this case the need for customer education is obvious. That's hardly anything you can do with a soldering iron.........or is it? 90% of fixing the stuff is communicating with the customer anyway.
Good luck !

[Station House Products]

Max-trac's suggestion was definately a good one! Document, document, document! At least if there is a problem down the road, they won't be able to drop the ball in your lap and say "well, he's the guy that installed them or was supposed to fix them properly".

As for the lecture with them, did they at least smile and nod their heads alot like the guys around here do? What your department needs is a radio officer (not a communications officer). This should be someone who has some knowledge of radios and their workings as well as someone who has the common sense to know when they are in over thier head and call in someone if the need arises. The chief of the dept. and/or the president of the company both need to back him up when he needs it as well.

The fact that a comm center can "hear you" does'nt mean that the radio "must be working OK". You may be close to a tower or reciever and they can hear you fine at that time, but what happens when $#!t hits the fan and you're out in the boonies somewhere and the radio does'nt work when you need it most? The department has just opened it's self up to a MAJOR laibility if someone gets hurt or more damage occured because additional apparatus or manpower could'nt be summoned due to poor radio performance.

This is a common problem around my parts as the company sees a great money saver by doing the work themselves. I usually get a call within 2-3 weeks asking me to come look at some various problem either with the radio or the lighting/siren package and I charge them for the diagnostic time as well as the repair. Winds up costing them more in the long run usually due to the fact that the repairs are generally more than what it would have cost them to have the instll done properly. One of my guys is always saying "Pay me some now, or pay me more later" and I could'nt agree with him more.

Show this thread to your officers and let them know that unless the radios are installed and tuned properly, you want no part of it now or in the future, and you want a letter from them abstaining you from any liability for work currently performed. There's a reason why we pay so much money for insurance in this business. LIABILITY.

[Brentd2183]

Ok, so a little update. I finally recieved a cutting chart via email from Comtelco, check the part numbers for the antenna to see what they have and the one officers truck i went over and measured was actually pretty close, maybe within half an inch. Also he is the guy who knew better than to cut the coax so he ran the extra up to the radiator and back, good guy, used to be a mechanic. My question is this, the radio's are 60watt Ritron patriots. How can my meter actually read more than 60 watts???? Mine has two needles, one for forward, and one for reflected, where they cross gives me the SWR. IF it was super bad i would get like 55 reflected and 5 out. How can the meter goto like 120watts on forward?? What does a short on the coax read on a meter? Thanks guys, i will get this mess sorted.
Brent

[nmfire10]

Uh, you can cut the coax to an appropriate length. There is nothing wrong with that. In fact, you're better off cutting it to a proper length rather than running the extra all over the place.

What kind of meter are you using?

[Brentd2183]

Im using a Vectronics VEC-730, its for 1.8-60mhz. Ok, so the length of the coax on a twoway antenna doesnt mean anything as far as matching the length of the antenna system to the radio, only cutting the whip. I was always under the impression that the radio sees everything from the connector to teh tip of the whip as one piece and the standard i think 17feet of cable was supposed to stay that way because as a whole with the correct whip length you'll get that money spot for lowest SWR. If thats the case that eliminates one more issue, last one is what does a short look like a on watt meter. I got more of a description two posts up.
Thanks again
Brent

[va3wxm]

The only reason you wouldn't cut the coax is if it's somehow part of the antenna system (counterpoise).

A lot of el-cheapo magmount chicken-band whips used to warn not to cut the cable because it served as the "other half" of the antenna.

A properly installed antenna using the vehicle as its groundplane doesn't give a damn how long the coax is.

[tvsjr]

Im using a Vectronics VEC-730, its for 1.8-60mhz. Ok, so the length of the coax on a twoway antenna doesnt mean anything as far as matching the length of the antenna system to the radio, only cutting the whip. I was always under the impression that the radio sees everything from the connector to teh tip of the whip as one piece and the standard i think 17feet of cable was supposed to stay that way because as a whole with the correct whip length you'll get that money spot for lowest SWR. If thats the case that eliminates one more issue, last one is what does a short look like a on watt meter. I got more of a description two posts up.
Thanks again
Brent

Why would you look for a short on a wattmeter? Take your DVM and check for continuity between shield and center. Don't overcomplicate matters.

[Max-trac]

Usualy lowband whips down on the side of the car will not tune up flat, so you just have to use the chart and hope for the best. (of course check for opens and shorts).
A better antenna is a NMO base loaded 1/4 wave in the middle of the roof or even trunk lid.
Remember the wavelength is LONG on lowband, ie get as far away from any metal as you can. And don't try to tune the antenna parked next to a metal building etc....

[Brentd2183]

Thanks guys, good to know that the coax length shouldnt be cut only in the counterpoise antennas, learning new things everyday. And yes TVSJR, i use a my elec meter for shorts, but was curious what a short would look like on a watt meter. I will be at a meeting tonite and will throw the meter back on other peoples radios and know with a cutting chart in hand i'll see what i come up with. Thanks for all the help with this one.
Brent

[va3wxm]

but was curious what a short would look like on a watt meter.

It may not look like anything. In certain situations what is a DC short is not an AC short (RF is a type of AC current).

For your typical 1/4 wave groundplane a short between the radiating element and the groundplane will mess things up big time.

But if you've got a 5/8 wave with a tapped base coil (for impedance matching) that antenna will show a DC short but will radiate RF perfectly fine.

[Station House Products]

OK, now I feel like a real Richard Cranium. I thought he meant cutting the antenna whip. I swear, I'm off the bottle for real this time!