Batboard

Had a mobile user (VHF Hi), tell me his antenna lead broke recently and he took it to a garage for a quick fix. Antenna is a 3db NMO trunk deck mount. When he described it to me, I just HAD to look. The center lead and shield had broken loose from the NMO mount. The garage had soldered a 12" piece of 14 gauge hookup wire to the center conductor and attached an electrical quick connect to the wire and female to the center conductor of the coax. For grins and giggles, I checked the forward and reflected power. 30 watts forward, 15 watts reflected.

After the repair, I was showing 42 watts forward and couldn't measure the reflected (on the 5watt scale the meter barely moved).

<sigh>

Thats right up there with the guy who screwed bolt into the antenna connector on a radius portable.

FireCpt809 wrote:Thats right up there with the guy who screwed bolt into the antenna connector on a radius portable.

Well, if the portable was UHF and the bolt was about 6" long, think of the power handling capabilities.

Users on an 800 trunked system; want 'more range'. They 'have a buddy who does CB', tells them them bigger the antenna the better. Soooooo, they take off the 800 MHz, gain antenna & put a 27 MHz antenna on the NMO mount. THEN they come into the shop, complaining they can't talk on the system at all.

The first few dozen times it happens you try to educate them. But it keeps happening. The bill to the office is small enough and rare enough to not ring an alarm. So it still happens.

Finally, you just curse under your breath.

You can't fix stupid.

hey it's cool....if we get 25 watts with 12 volts we should get 50 watts with 24 volts

right??

Riggggghhhhhhhhhht.

Yeah, let me know how that's working out for you.

escomm wrote:hey it's cool....if we get 25 watts with 12 volts we should get 50 watts with 24 volts

right??

Just don't hook up to the -48 bus. You'll get 100 watts, but all the RF will be upside-down.

But that's how I tell people to make it so nobody else can listen to them - turn the radio upside down, and that inverts the sine waves; the other guy has to do it too.

tvsjr wrote:

escomm wrote:hey it's cool....if we get 25 watts with 12 volts we should get 50 watts with 24 volts

right??

Just don't hook up to the -48 bus. You'll get 100 watts, but all the RF will be upside-down.

that darn'd blasted voice inversion!

Andy Corbin wrote: For grins and giggles, I checked the forward and reflected power. 30 watts forward, 15 watts reflected.

eh it should be fine
as a testament to the quality of Motorola radios,
We have a older uhf mobile at work setup as a base, maybe a maxtrac, not sure
4 years ago someone disconnected the antenna and removed it.
Its been in use transmitting periodically every day since then with no antenna.
I thought it would die after a few days, but amazingly it keeps going!

gopher wrote:

Andy Corbin wrote: For grins and giggles, I checked the forward and reflected power. 30 watts forward, 15 watts reflected.

eh it should be fine
as a testament to the quality of Motorola radios,
We have a older uhf mobile at work setup as a base, maybe a maxtrac, not sure
4 years ago someone disconnected the antenna and removed it.
Its been in use transmitting periodically every day since then with no antenna.
I thought it would die after a few days, but amazingly it keeps going!

I know most modern transmitters have SWR foldback protection built in and can handle a dead short or an open line, or anything in between.
I knew the antenna system I was looking at was way out in left field and was unacceptable in its current configuration, BUT, my curiosity got the better of me so I just had to take a measurement.

I had a utility truck driver snap off his 900mhz Motorola whip antenna. He took a piece of 14g solid wire, stripped it and made a new 3db gain 900mhz antenna open coils and all. Then he clamped it in between the chrome nut and nmo mount. If he hadn't shorted it out it probably would have worked.

I had a guy try to sell me "gain" coax. He sold it by the linear foot!

No. Please, tell me this was just a bad pun. I've seen stupid people, I've seen my share of shysters, and stupid shysters, but 'gain' coax?? Nawww...

kb4mdz wrote:No. Please, tell me this was just a bad pun. I've seen stupid people, I've seen my share of shysters, and stupid shysters, but 'gain' coax?? Nawww...

Hey, the Motorola sales forces suckers public safety agencies to buy extra features they don't need all the time. Surprised that they haven't come up with something like this. Wouldn't put it past them trying.

Jim

The sad thing is that if we could find an analog to erbium doped optical fiber, but for RF, you *could* have a transmission line with gain.

Of course, if I could find a sufficient quantity of negative-mass matter I could build a stable wormhole....

kb4mdz wrote:No. Please, tell me this was just a bad pun. I've seen stupid people, I've seen my share of shysters, and stupid shysters, but 'gain' coax?? Nawww...

I recall back around 1970 there really was some outfit that was nationally marketing "gain coax". The target market was primarily CB but I don't doubt that some salesmen tried to hawk it to two way business and public safety customers.

On the subject of stupid shysters, I was pestered incessantly back in the 90's by a salesman that claimed they had VHF and UHF mobile antennas that would eliminate intermod and interference by high Q resonance tuned to the users frequency.

I kept telling him I was not interested because I did not want the hassle of critically tuning mobile antennas, if it did indeed have narrow bandwith it would not handle 5 MHz tx/rx separtation for repeater operation and the attention off resonance could not be more that a few db and not sufficient to eliminate interference. He kept calling insisting that if their antennas were properly tuned they would pass all user frequencies and block other in-band signals.

It was also a low profile antenna but they claimed very high gain to due resonance effects.

The radio shop that services the dept radios has a section above the door called the "Wall of Flame" There are pieces of installs and re-installs hanging up there that make you shake your head....pigtail fuses with a bypass wire crimped on both ends...ground wires spliced to power wires....coax repaired with wire nuts.....

Fowler

It is now your duty to take digital pictures of those pictures and share them with the interwebs.

kb4mdz wrote:But that's how I tell people to make it so nobody else can listen to them - turn the radio upside down, and that inverts the sine waves; the other guy has to do it too.

There is a retailer here in town that uses CP100's. One day I was in there and I noticed they were holding the radios upside-down when they talked. I asked why, and the cashier said it was to prevent people with scanners from hearing them. My reply: "Really?" She said a couple of the managers tested it and it worked!

kb4mdz wrote:You can't fix stupid.

k2hz wrote:

kb4mdz wrote:No. Please, tell me this was just a bad pun. I've seen stupid people, I've seen my share of shysters, and stupid shysters, but 'gain' coax?? Nawww...

It was also a low profile antenna but they claimed very high gain to due resonance effects.

Back in the mid-70's, there was a shyster who ran a CB shop near the I-80 truck stop in Council Bluffs who was marketing a lubrication
product he called "Antenna Slick." The idea was to lube the antenna rod and make it slippery "so those pesky little SWRs can't hang on."

"There is a retailer here in town that uses CP100's. One day I was in there and I noticed they were holding the radios upside-down when they talked. I asked why, and the cashier said it was to prevent people with scanners from hearing them. My reply: "Really?" She said a couple of the managers tested it and it worked!"

Speech Inversion Encryption......

Fowler

abbylind wrote:

"There is a retailer here in town that uses CP100's. One day I was in there and I noticed they were holding the radios upside-down when they talked. I asked why, and the cashier said it was to prevent people with scanners from hearing them. My reply: "Really?" She said a couple of the managers tested it and it worked!"

Speech Inversion Encryption......

Fowler

All the RF fell to the floor.

It probably cut down the range of the portables having the antenna next to their arm. Similar to working from a belt loop.

OLD story, but along the same storyline...At the Freeport mine in Globe, AZ, a worker broke off his highband 1/4 wave, so he fabricated a nifty gain antenna and shoved it through the rubber.
The coil/whip combo was 29", and the coil diameter was 3", with 6 turns spaced at about 1/2".

He was less than a 1/4 mile from our repeater, and it could not hear him..I wonder where that RF went?
We saved that 'antenna' for about a year before we tossed it, but did let the mine super take a look, and he immediately told his men to NEVER play with the radio system.
THEY learned, others never do.
The other mines never gave us as many fits with dump truck techs as FMI did, but they also did their share of field mods....And those foil wrapped glass fuses, and the ATC fuses with wire around the blades scares the hell out of me.
I can see it now....A truck fire in a desert surrounding, with flammable chemicals and few people able to assist in time...