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If you transmit without the correct antenna.

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Motoballa

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Hey! :)

I don't know how true this is, if someone transmits 800MHz on a 400MHz Antenna, would it destroy the radio? What would the outcome be? I'm receiving just fine, its even a stubby antenna, wasn't sure how it would affect the radio.
 

paulears

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Most portable radios have pretty poor aerial systems. The ideal would be a resonant antenna, that has a VSWR of 1:1, and does it's job of getting all the power away, returning none to the transmitter.

The reality is on most professional equipment, that antennas are never remotely perfect. They get bend, squashed, loose, intermittent and the match is far from perfect. It would be a poor transmitter design that meant this kind of thing caused failures. People even forget to connect the aerial to the set - or perhaps screw on a VHF instead of a UHF. It's still a bit of wire, and while performance drops - close in, it still works.

The electrical issue is that reflections from non-resonant aerials need to be coped with. With hand held gear, the power involved is relatively low. In a TV broadcast transmitter, it could be mega high, so even small antenna mismatches can cause pretty substantial reverse power, which can, and does cause damage. In all my years I've never damaged a transmitter with faulty, or the wrong aerials connected. Most decent gear monitors the output, and as VSWR rises, power output is reduced to cope Running your typical radio into the wrong aerial wouldn't concern me at all with modern gear.
 

Motoballa

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Most portable radios have pretty poor aerial systems. The ideal would be a resonant antenna, that has a VSWR of 1:1, and does it's job of getting all the power away, returning none to the transmitter.

The reality is on most professional equipment, that antennas are never remotely perfect. They get bend, squashed, loose, intermittent and the match is far from perfect. It would be a poor transmitter design that meant this kind of thing caused failures. People even forget to connect the aerial to the set - or perhaps screw on a VHF instead of a UHF. It's still a bit of wire, and while performance drops - close in, it still works.

The electrical issue is that reflections from non-resonant aerials need to be coped with. With hand held gear, the power involved is relatively low. In a TV broadcast transmitter, it could be mega high, so even small antenna mismatches can cause pretty substantial reverse power, which can, and does cause damage. In all my years I've never damaged a transmitter with faulty, or the wrong aerials connected. Most decent gear monitors the output, and as VSWR rises, power output is reduced to cope Running your typical radio into the wrong aerial wouldn't concern me at all with modern gear.


Great response, thanks! :)
 

Hatchett

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You also want to keep in mind... When you have an unknown antenna, or an antenna that is designed for another band, it never hurts to put an SWR meter to it an test it at the desired frequency. Sometimes you will be pleasantly surprised.

A lot of standard antenna designs will commonly have alternate resonate frequencies that align with other frequency bands.

Examples that I have ran into.

Standard 5/8 wave cellular AMPS antennas will often have a 1/4 wave resonate frequency right around the 2 meter band and/or VHF high LMR frequencies. I put many in use as 2 meter/ VHF high antennas without having to do any returning/trimming

6 meter antenna or vhf low band antenna that has good SWR on the CB band because the feedline just happens to be the right length to form a resonate matching section between the antenna and the CB

2 meter antennas that have good SWR at 440mhz because the transmission line just happens to be exactly the right length.

One extreme example is the main 10 meter antenna for my shack. It's a half wave vertical on top of a tower. It has about 80 feet of RG8 running to my shack. Oddly enough, it has about 1.3 to 1.5 SWR right around 146 to 147Mhz. The SWR quickly goes sky high if I get out of that range, but within that range it is almost right on the dot. Coverage reports around the area also indicate that it does a good job. The antenna is an electrical 3 wavelengths at that frequency. Evidently the coax (and other stuff in the feedline) is at exactly the right length to match the the high impedance of the multiwave antenna to the 50 ohms of the radio.

Wonder how that happened … (smiles)


In general 5/8 wave antennas will have a usable 1/4 wave resonate frequency way down from their designed frequency.

Longer antennas can often be used if you carefully trim your coax to achieve usable SWR on the desired secondary frequency. If your antenna is properly tuned for your primary resonate frequency, the coax trimming should not hurt you SWR on the primary designed frequency.

More complicated antennas can be matched by using 75 or 100 ohm matching sections to produce good SWR at a secondary frequency while not hurting the primary operating frequency too much.
 

prcguy

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I've tried to burn up countless radios on purpose transmitting for very long periods of time with no antenna connected and have never damaged a commercial 2-way radio or CB in doing so. Some radios are more susceptible to damage than others but for most part I think any modern 2-way radio should survive brief periods of transmit with the wrong or no antenna without any problem.
prcguy
 

gkjunk757

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Is there a general rule of thumb on transmitting using an out of band antenna? I need to use uhf and 800mhz on an APX radio but don't want to use the 2 foot antenna the handheld came with. I can't find a dual band stubby so should I use a uhf or 800mhz stubby antenna? Is it better to transmit out of band lower or higher than the frequency the antenna was designed for?
 

jonwienke

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Is it better to transmit out of band lower or higher than the frequency the antenna was designed for?

None of the above. Either can fry your radio, and will perform like excrement. HT antennas are cheap, there is no excuse for using an antenna not tuned to the band you're on. I have seen radios fried by TX without an antenna, or with a badly-tuned antenna.
 

cmdrwill

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The 'wrong antenna' can burn out the transmitter. Wrong antenna on a Baofang usually burns out the receiver. Even high dollar commercial radios come into the shop with burned up receive or transmit due to the 'wrong antenna'. The power has to go somewhere.....

So YES you do risk damage.
 

gkjunk757

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I understand there is a risk of damage but does anyone know which scenario would be safer or better performing? UHF antenna on the 800mhz band or 800mhz antenna on the UHF band? Are they both equally damaging or would one scenario be worse than the other? Thx!
 

jparks29

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I understand there is a risk of damage but does anyone know which scenario would be safer or better performing? UHF antenna on the 800mhz band or 800mhz antenna on the UHF band? Are they both equally damaging or would one scenario be worse than the other? Thx!

Depends entirely on the antenna, location, etc.

Just as an example... a 1/4 wave 2m antenna is roughly 3/4 wave on 70cm.... So there is usually an OK match...but the radiation angle puts the signal in the sky....

An open coil 5/8 over 1/4 on 800 Mhz is also resonant ~165Mhz

Just stick to the antenna and freq. range designed for use with the radio. No reason to risk it.
 

jim202

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Is there a general rule of thumb on transmitting using an out of band antenna? I need to use uhf and 800mhz on an APX radio but don't want to use the 2 foot antenna the handheld came with. I can't find a dual band stubby so should I use a uhf or 800mhz stubby antenna? Is it better to transmit out of band lower or higher than the frequency the antenna was designed for?

Why do users of radios always think they know better than the vendor design engineers? Just because the antenna is too long for your liking's, doesn't mean that gives you the choice to change it because you don't like the length. If you run up against the right supervisor, you just might be paying for the repair to that radio.

The use of stubby antennas is a poor choice for a public safety user. It is a poor antenna and reduces the range of the radio drastically. One of these days you will be inside a building or out on the far reaches of the tower coverage and you find your portable doesn't get back to the dispatcher. You have some thug beating on you and you can't be heard trying to call for help. Just remember it was your choice to put the stubby antenna on your department radio.

Making unauthorized changes to department equipment could open up the door to all sorts of legal issues for yourself. Like if your injured and the radio didn't work due to you making non authorized changes to it, you could be footing the doctor bills your self. The list of ramifications to your job will just keep piling up.
 

jparks29

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Why do users of radios always think they know better than the vendor design engineers? Just because the antenna is too long for your liking's, doesn't mean that gives you the choice to change it because you don't like the length. If you run up against the right supervisor, you just might be paying for the repair to that radio.

The use of stubby antennas is a poor choice for a public safety user. It is a poor antenna and reduces the range of the radio drastically. One of these days you will be inside a building or out on the far reaches of the tower coverage and you find your portable doesn't get back to the dispatcher. You have some thug beating on you and you can't be heard trying to call for help. Just remember it was your choice to put the stubby antenna on your department radio.

Making unauthorized changes to department equipment could open up the door to all sorts of legal issues for yourself. Like if your injured and the radio didn't work due to you making non authorized changes to it, you could be footing the doctor bills your self. The list of ramifications to your job will just keep piling up.

There was an agency that was using T-band, MOST officers' vehicles had 'high gain' antennas on them, yes with a loading coil, IIRC they were 5/8 over 1/2 wave..... We'll call them county A

Well, a neighboring county was ALSO on T-band, we'll call them county B, had great coverage (actually, too good coverage, had simulcast issues), and used 2 1/4 wave antennas in cophase to minimize the simulcast issues..,

Well, county A's officers didn't want HUGE antennas.... so, every once in a while, I'd get a car in the shop with 'poor coverage/poor audio/can't talk' etc... and come to find out the guys were buying 1/4 wave UHF antenna's, NOT tuned to frequency, and just plopping them on their cars... (NMO = unscrew off, screw on). So, unity gain, and tuned off frequency.... I'd pull their old antenna out of the trunk, put it back on, make sure SWR was good, radio check and off they went.... 9/10 there was no damage to the radio....

Well, county C comes into play, and has an 800 Mhz system, with 1/4 wave whips... and wouldn't you know... now the antennas are even smaller and even COOLER! Pssht.. Why does county A need these 40" antennas when county C has these cool little 3" antennas?! So, yup.. County A officers start coming BACK in, wanting smaller antennas... NOPE....


Anyway, I had this one officer... came in.. NO RX, NO TX......Said it was working OK, then RX was working but had a hard time hitting repeaters... then it wouldn't do anything..... Sure enough, had a 4W portable 3ft away transmitting into the car and barely broke squelch, and portable was deaf on mobile TX.. Took me a second to realize he was running the normal 5/8 over 1/2 wave, but half the whip was missing.. Asked him if he hit a low hanging branch or something... nope... He cut it.... He told me how he saw County C with short antennas and wanted a short one too, so he cut it off....

Now, before this, most officers that did stupid stuff ended up paying for stuff out of pocket, otherwise I have to bill the agency and they get their peepee smacked for effing with county equipment.... But it was usually something like a $35 antenna and a 'don't do that, dumba$$'....

Not this time.. He was transmitting into an 'antenna' that had almost 40% reflected power..... about 20W back into the radio... Toasted the front end and the PA......

Shortly afterward, a memo went out advising that ANY officer that effs with their radios will be paying out of pocket for ANY repairs... and that pretty much stopped that..

STILL couldn't get them to stop grabbing their portables by their antennas though... Lots of replaced connectors and stripped threads....
 

kb4mdz

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Apr 28, 2003
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Garbage truck drivers who have been told by their 'buddy' that a bigger antenna does better. 800 MHz radios. Drivers put on CB fiberglas helically wound sticks. Come to shop complaining of range issues. Argue with the tech about 'my buddy said...'

Another one was a SCADA system on 900 MHz, spread spectrum, with Yagis. Water tank painters were up on the tank, SCADA owner asked about the RF link fading in & out. Similar; painters thought a bigger antenna would do better. Connected to a DB224 VHF dipole array, omni pattern. SCADA owner couldn't understand why it didn't perform any better. (besides the original SCADA install being ****ty & then degraded more over time with no PM program).

As for the ones that pick up radios by the antenna? I quietly yell at them to not pick it up by the handle. Then ask them if their Mama picked them up by their handle? Some, it takes a few seconds to sink in. Some get it right away. Some answer 'YES!' Those are the ones I tell 'that's why you're a FF/Cop, it pulled half your brains out of your head'

JPARKS, did that guy have to pay for the radio out of his own pocket? I hope so. I'm to the point now that if someone showed up in my shop like that, I'd call his boss, explain the SITREP, ask permission, then borrow my Marine co-worker to do a Full Metal Jacket DI routine on his face.
 
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jparks29

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As for the ones that pick up radios by the antenna? I quietly yell at them to not pick it up by the handle. Then ask them if their Mama picked them up by their handle? Some, it takes a few seconds to sink in. Some get it right away. Some answer 'YES!' Those are the ones I tell 'that's why you're a FF/Cop, it pulled half your brains out of your head'

I can't complain too much about it though, I'm guilty of it too, hahaha....

JPARKS, did that guy have to pay for the radio out of his own pocket? I hope so. I'm to the point now that if someone showed up in my shop like that, I'd call his boss, explain the SITREP, ask permission, then borrow my Marine co-worker to do a Full Metal Jacket DI routine on his face.


Dunno. County provided radio, billed labor to the agency...

Don't even get me started with 'we'll let our fleet mechanics install the radios' crap.... but we're starting to get off topic.. :p
 

cmdrwill

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IDon't even get me started with 'we'll let our fleet mechanics install the radios' crap.... but we're starting to get off topic.. :p

Not off topic, the 'fleet mechanics' probably do NOT know anything about antennas and correct installation of antennas either.

Most all of the so-called pro radio installers around here do not even have a clue how to correctly install a antenna, let alone the correct antenna for the radio.
 
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