Will transmitting on CB or Ham radio damage scanner?

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wise871

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Like many of you I have a mixture of scanners and ham radios in my collection. I was told by a friend that it is best to shut off the scanner before transmitting on a ham radio. Over time it can cause damage to the scanner. I noticed the other day while in my car that when I was talking on the ham radio, my scanner would stop whatever transmission it was on until I released the mic. For now I make sure I turn my scanner off when I want to talk. I noticed in the picture forum that many of you have a large selection of ham radios and scanners. Do you turn the scanners off? Thanks
 

ArtU

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HI,
your scanner stops scanning when you transmit because the front end receiver is overloaded with a signal. Unless you are transmitting directly into the connector of the scanner this should not hurt it.

My FT-60 HT will white noise out while siting on the console when I key up on the CB, RF front end overload. Again if correctly manufactured this does not hurt the unit.

Direct injection of RF power into the receiver connector can however. I doubt you have your antennas that close together for that to happen.

Think about all the radios the Public Safety folks have running all at the same time on the tree mounts.

ArtU
 

Boilermaker

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I've operated ham and CB transceivers with scanners and AM/FM/SW receivers nearby and haven't had any damage. Radios that are receiving during transmit will sometimes overload (as ArtU described) but, there won't be any permanent damage.
 

RodStrong

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I have never known this to be a problem. Been doing it for years with no known effects in multiple vehicles.

At the moment, I have a work vehicle with 110 watt VHF, 50 watt UHF, and 35 watt 700/800 mobiles mounted adjacent to two scanners, one an older Pro 2026 analog and another a newer Pro 197. Also a CB as well. All the antennas are in close proximity to each other as well. Have used this combination in this vehicle daily for 2 years with not a single issue.

Good luck.
 

jackj

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You will not damage the scanner unless it is hooked to the same antenna without any type of isolation. If the scanner is operating using a seperate antenna then you don't need to worry. You don't need to turn off the scanner either unless it is making noise and bothering you. Anything that doesn't destroy a transistor won't hurt it. Heat is the only exception, with heat the damage is cumulative.
 

jim202

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I am glad to hear all you expert radio techs giving advice to someone that is asking a reasonable
question. Holy cow, I wish I got a steak dinner for all the radios that I have had to repair over the
years from front end damage due to strong RF getting into the radio. Even the commercial radios
like GE, MA-COM, Motorola, Kenwood, ICOM, and so on have not provided enough front end
protection to put the RX antenna right next to a high powered TX antenna. The FET transistors
don't like all that high voltage across the junctions in the transistors.

A little common sense goes a long way here. Keep the antennas separated as far as you can.
Keep the TX power down as much as you can.

Bottom line here, if you don't believe what I am saying, go visit a good radio shop and see what
they tell you. In the 45 plus years I have been in this field working on everything from ham radios
to engineering cellular sites, I have seen a bunch of both good and bad practices. Do as you want,
but be prepaired to fix some of your radios if you place a scanner antenna close to a TX antenna.
In time you will find the receiver going deaf. It will happen. Might not happen the first time you
key the transmitter. Might not happen till the 1000th time, but given enough time, you receiver
won't hear as good as it use to.

Jim




You will not damage the scanner unless it is hooked to the same antenna without any type of isolation. If the scanner is operating using a seperate antenna then you don't need to worry. You don't need to turn off the scanner either unless it is making noise and bothering you. Anything that doesn't destroy a transistor won't hurt it. Heat is the only exception, with heat the damage is cumulative.
 

ArtU

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I am glad to hear all you expert radio techs giving advice to someone that is asking a reasonable
question. Holy cow, I wish I got a steak dinner for all the radios that I have had to repair over the
years from front end damage due to strong RF getting into the radio. Even the commercial radios
like GE, MA-COM, Motorola, Kenwood, ICOM, and so on have not provided enough front end
protection to put the RX antenna right next to a high powered TX antenna. ...

<snip>

Jim
Hi Jim, where in the posts have you seen the fact that the Scanner RX antenna and the TX antenna are close together?

I have repaired front end damage like you have, but because someone put and antenna right next to another one, or in a bench test setup transmitted direct into an RF front end.

I doubt our friend with the scanner has his scanner antenna right next to his Transmitter antenna. For reference, lets call right next to the direct near field.

How about contest hams that have $4500 1500 kilowatt stations transmitting right next to their pet $3800 dual HF receiver receiver that is band scanning and spectrum plotting their next QSO while they are transmitting at the same time?

Yes their antennas are in the same yard and not right next to each other, but the radios and that 1.5K amp is on the same desk right ?
 

K4APR

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I am glad to hear all you expert radio techs giving advice to someone that is asking a reasonable
question. Holy cow, I wish I got a steak dinner for all the radios that I have had to repair over the
years from front end damage due to strong RF getting into the radio. Even the commercial radios
like GE, MA-COM, Motorola, Kenwood, ICOM, and so on have not provided enough front end
protection to put the RX antenna right next to a high powered TX antenna. The FET transistors
don't like all that high voltage across the junctions in the transistors.

A little common sense goes a long way here. Keep the antennas separated as far as you can.
Keep the TX power down as much as you can.

Bottom line here, if you don't believe what I am saying, go visit a good radio shop and see what
they tell you. In the 45 plus years I have been in this field working on everything from ham radios
to engineering cellular sites, I have seen a bunch of both good and bad practices. Do as you want,
but be prepaired to fix some of your radios if you place a scanner antenna close to a TX antenna.
In time you will find the receiver going deaf. It will happen. Might not happen the first time you
key the transmitter. Might not happen till the 1000th time, but given enough time, you receiver
won't hear as good as it use to.
Jim hit it right on the nose! There is a very high risk of damage to a front end of a scanner when transmitting in close proximity, especially when the antennas are only feet apart.

With the press for more and more sensitive receiver front ends, (exp. 0.2-0.1 uV) the front ends are not as protected and filtered to increase this sensitivity. With that lower protection brings greater risk of doing direct damage from brute force RF. Amateur gear is especially prone to this. The Yaesu FT-8800 comes to mind. That particular model had a bad habit of losing it's front end with as little as a 20W transmitter within feet. The worst part, the FET that was blown was way down in the board and and virtually impossible to get to.

Scanners are just as much at risk with the front end sensitivity demanded by today's hard core enthusiast.

When I was still with Motorola, we regularly had news teams coming in to have scanners (usually Unidens) installed in their mobile reporting vehicles. They usually also had a 100W Mitrek or Spectra installed in that vehicle as well. We always made it a point to get the scanner antenna as far from the transmitting antenna as possible.

So as was said before, keep the antennas as far from each other and use the lowest power required to maintain amateur communication. Besides, the second part is part of the rules and you should be doing that anyways.

Lastly, simply turning off the scanner will not protect the front end. RF can get in just as easy because turning it off does not disconnect the antenna from the scanner. Unless you have some kind of RF relay inline to disengage when power is off.
 

ArtU

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<snip>

Lastly, simply turning off the scanner will not protect the front end. RF can get in just as easy because turning it off does not disconnect the antenna from the scanner. Unless you have some kind of RF relay inline to disengage when power is off.
Very good point above Jason.

Again, how far apart are we taking here guys on the antennas?
 

W6KRU

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Very good point above Jason.

Again, how far apart are we taking here guys on the antennas?
I have seen a few numbers thrown around for that but it is usually a quarter wavelength minimum with a half wave length even better but I think there might be a little more involved than that. The type of receiver and the power of the transmitter would affect the distance needed in my opinion. In practice, I just go for the max possible and lean to safe side. My HF antenna is on the spare tire carrier of my Bronco, the VHF/UHF is on the roof, and I put a mag-mount on the front cowl for the scanner. I have never keyed the HF rig with the scanner connected to an antenna. I use the vhf/uhf rig at full power and don't worry about it. So far so good.

When running HF at 100 watts, there is so much RF around that the defroster wiring in the rear window gets enough RF to flicker the DF indicator in the dash, in sync with the modulation level even when the DF is turned off.
 

DPD1

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It can happen with other stuff too. I've heard from a lot of people that have blown out their GPS/MURS dog trackers with CBs, or blown out their GPS with CB or MURS. Or CB vs MURS or whatever. It's fairly common.
 

wise871

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Here is a screen shot of my antenna seperation. The only difference is the front antenna is a 12" Comet B-10NMO for my ham radio and the rear is a Maxscan 1000-B.
 
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ArtU

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It can happen with other stuff too. I've heard from a lot of people that have blown out their GPS/MURS dog trackers with CBs, or blown out their GPS with CB or MURS. Or CB vs MURS or whatever. It's fairly common.
Hi, I am calling "that it is not fairly common."

Besides being in the industry,I have GPS, CBs, vhf-uhf ham, and 120 watt hi-power HF ham radio in my truck cab; all next to each other for a decade and no problem. I have all the same and more in my trailer.

I have very sensitive GPS receivers that survive at 100K feet altitude, 900mz hi-power Telemetry transmitters, s-band hi power video transmitters all in a rocket payload section; and the GPS does not blow.

I know how things can get damaged, but some of this speculation is going way too far.

I would ask that folks do not toss out rare issues and get the majority of folks worries about issues that will not effect them; rather then talk about normal issues and those rare issues.
 

DPD1

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Well, I had about five people last year alone, ask me about MURS GPS mobile setups, because they had already ruined a GPS. I'd say that's more than speculation. I think it's better people know about the possibility than act like it's never going to happen.
 

K4APR

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I have seen a few numbers thrown around for that but it is usually a quarter wavelength minimum with a half wave length even better but I think there might be a little more involved than that...
This is a fairly good starting point. Keeping at least a 1/4 wavelength apart of the lowest frequency range is good to avoid coupling and detuning, but can still be too close to avoid the RF exposure from one to the other. So again, take accessment of your vehicle and decide on what are the furthest points you can mount the antennas from each other.

I have a Chevy Impala and I chose to mount my three antennas on the trunk lid. Looking at the back, from left to right, I have: VHF/UHF Dual (amateur), 800 MHz (PS) and 5/8 VHF (amateur/aprs). This set up is working well for me. The only radio that transmits much is the APRS radio and I have it set at about 35W.
 

jim202

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Art, the main point your missing here is the type and quality of the RX front end of the equipment
that is being used. There is a huge difference in the receiver that has a narrow front RX system with
tuned cavities over the cheap radio that has nothing but a front end that goes from DC to white light.
I have seen the front end of commercial two way equipment blown from overload.

In the case of my own equipment, I have had the RX front end blown by a UHF radar system that
I use to drive by each day. the solution was to add a couple of hot carrier diodes from the gate
of the FET to ground. This limited the max peak to peak voltage to the FET.

As for the ham stations running all sorts of power for field day and the likes, given the placement
of the antennas, yes they will blow the front ends up. have seen it happen on a number of
occasions. With some careful placement of the antennas and maybe some mods to the
receivers, this won't happen the next time. I am talking about some serious contest people
that spend months getting ready for the weekend. Even they bring extra radios just in case
they wipe out one of their receivers.

Don't down play this issue. It is real and people need to be aware of the damage that can
happen. Bottom line is to try and space antennas as far apart as possible. In the size of
the roof on vehicles today, that is not easy. If you look on the roof of any of the public
safety mobile command vehicles, you will see that there is little space left open. Normally
the radio geek that had a hand in laying out the antennas on the roof will interleave the
different band antennas in between the VHF ones. Like a VHF then a UHF then an 800
and start all over again. It can be done, but takes some care in the original layout to do it.

Jim




Hi, I am calling "that it is not fairly common."

Besides being in the industry,I have GPS, CBs, vhf-uhf ham, and 120 watt hi-power HF ham radio in my truck cab; all next to each other for a decade and no problem. I have all the same and more in my trailer.

I have very sensitive GPS receivers that survive at 100K feet altitude, 900mz hi-power Telemetry transmitters, s-band hi power video transmitters all in a rocket payload section; and the GPS does not blow.

I know how things can get damaged, but some of this speculation is going way too far.

I would ask that folks do not toss out rare issues and get the majority of folks worries about issues that will not effect them; rather then talk about normal issues and those rare issues.
 

jackj

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You guys are making a mountain out of a mole hill. I have worked in the communication field all of my life. I have an Advanced Class ham ticket (N8BSR) and I have worked Field Day on several occasions, always barefoot. My rigs ran about 250 w.pep. I have NEVER blown the front end of my rig or anyone else's rig. Of course we don't put our antennas on top of each other either. I have had to replace RF amps in commercial 2-way equipment on several occasions but not more frequently than I have had to replace IF amps. I have had several scanners over the years, both in my cars/trucks along side of ham/commercial 2-way radios as well as sitting on my bench at home. I have NEVER had an RF amp fail in any of my scanners.

Use common sense and keep scanner antennas separated as much as possible from transmitter antennas but don't get paranoid about it. Don't try to use the same antenna for both your scanner and your transmitter.
 

ArtU

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......the solution was to add a couple of hot carrier diodes from the gate
of the FET to ground. This limited the max peak to peak voltage to the FET.

......<snip>

Jim
Hi Jim, I actually thought about "a solution" for those that are worrieds this morning; but your post came out first.

For example I have dual receivers radios that let me transmit at 50watts out while the other receives just fine without blowing out when the signals are right next to each other; even on the same band. We do not see those types of radios blowing out very often.

I know the print generally showed two diodes back to back on the RX front end on most two-way radios.

So your solution is to add a couple of hot carrier diodes from the gate of the FET to ground. I like this solution.

This provides a solution to those that are worried and those that are not worried can rest on the numbers that more radios stay working then those that need fixing.

PPS: edit - This reminds me of the days when cable TV first came out. Many were saying if you put your TV on cable TV for a few years the front end got overloaded and weaker over time. When you put the TV back on the Antenna tower you were not able to pickup the far away stations you used to. That one never got myth busted either.
 
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