RF Damage to 396XT

[sflmonitor]

I have a 396xt scanner that I use in my car with a roof-mounted antenna. I also have a Moto Astro 110 watt Mobile in the same car. The antennas are installed as far apart as possible (approx. 3 feet).

I would like to know if anyone has had any experience with having RF damage caused to their scanner by having it installed so close to a powerfull transmitter. For now, I either turn off or disconnect the scanner whenever I have to transmit on the Moto just to be safe.

A few years back I damaged an Opto Electronics frequency counter by doing something similar, except it was with a 50 watt VHF ham transmitter. When I took it back to Opto Electronics, they told me that I had damaged it by transmitting too close to the unit.

 

[Gator596]

I have a 396xt which ocassionally wigs out whenever I transmit on the Astro xts3000 portable or vehicle transmitters we use at work. It just shuts itself off temporarily. I dunno if it does any damage or not... but the 396 is still going strong after at least a dozen times doing it.

 

[Danny6569]

rf damage

It will definetly damage youre scanner being that close to the other antenna! 3 feet is way too close to have these antennas together, if youre going to talk on this other radio, you need to cut the power way down from the 110 watts, and also even if you cut the power down you still need to give the antennas some space, it wont take much to damage that scanner!

 

[sflmonitor]

That's what I though and that's why I always shut the scanner off or disconnect the antenna. But I must admit that I have forgotten a time or two and transmitted while the scanner was on. I was lucky then. It cost me a few dollars to get the frequency counter repaired. I'll be willing to bet that it will be a bit more expensive to repair a 396.

Anyone have any ideas what a safe antenna separation distance would be? And I can't turn down the power on the Moto, it's a work radio.

 

[rfradioconsult]

Just turning it off may not offer any protection especially the passive components in the RF amp front end and may even fry the RF amp, even with the power turned off.

 

[jim202]

I had a VHF mobile radio front end FET get cleaned out by a 1.8 GHz radar at a facility I use to work
at. Solved the problem by connecting up 2 hot carrier diodes back to back on the FET input from the
antenna line. I put a couple of resistors in series with the feed source and tied the diodes to the
center point of the 2 resistors. This gave the diodes a chance to do their job, but not effect the normal
operation of the front end FET amp. Forgot to mention that the other end of the 2 diodes went to
ground.

What the 2 diodes did was limit the max voltage that could possibly get to the FET gate or input. The
resistors acted as a limiter to allow the diodes to work and not short out from too much voltage and
current flowing with a strong signal coming into the antenna.

The radar might not seem to be much, but it used a 150 foot dish and operated at something like
2 megawatts of pulsed RF power output. The feed horn was about 200 feet from the road. It blew
out the front end of my Master II mobile 2 times before I added my fix with the hot carrier diodes.

Jim

I have a 396xt scanner that I use in my car with a roof-mounted antenna. I also have a Moto Astro 110 watt Mobile in the same car. The antennas are installed as far apart as possible (approx. 3 feet).

I would like to know if anyone has had any experience with having RF damage caused to their scanner by having it installed so close to a powerfull transmitter. For now, I either turn off or disconnect the scanner whenever I have to transmit on the Moto just to be safe.

A few years back I damaged an Opto Electronics frequency counter by doing something similar, except it was with a 50 watt VHF ham transmitter. When I took it back to Opto Electronics, they told me that I had damaged it by transmitting too close to the unit.

 

[sflmonitor]

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Just turning it off may not offer any protection especially the passive components in the RF amp front end and may even fry the RF amp, even with the power turned off.

Will disconnecting the antenna avoid this issue?

 

[phatboy48]

Disconnecting the antenna will protect the scanner's front end devices from incidental RF damage. I recommend that you leave the scanner disconnected at all times that you are not actually using it. If you were to connect a watt meter to the scanner's antenna, in series with a 50 Ohm dummy load and transmit on that hi power VHF rig, don't be surprised to see several watts of power being indicated. That is that same as connecting a hand-held rig directly to the scanner antenna port and hitting the transmit button.

John

 

[jackj]

It is possible to damage the front-end of your scanner by applying too much power to it. But if the antennas are 3 feet apart and the transmitter is only putting out 110 watts then I don't think you have anything to worry about. You are out of the near-field of the transmitting antenna and the amount of power coupled into the receiving antenna should be less than what would be needed to damage your scanner. I used a scanner for years in the same truck with a 100 watt UHF mobile without damage to the scanner and both antennas mounted on the cab roof.

 

[mharris]

I have a 996XT mounted next to a VHF 110W and UHF Mid Power Astro Spectra. The antennas are not even three feet apart all roof mounted with NMO mounts. I have not had any problems transmitting even with the scanner on. I will say that it's very seldom I transmit in high power on either Spectra though.

 

[sragen]

I have a 996XT mounted next to a VHF 110W and UHF Mid Power Astro Spectra. The antennas are not even three feet apart all roof mounted with NMO mounts. I have not had any problems transmitting even with the scanner on. I will say that it's very seldom I transmit in high power on either Spectra though.

I have a similar setup, a 100W VHF and 25W UHF mobile's whose external antenna's are closer than 3 ft to the internal 996XT scanner antenna. I have had no problems.

In any event, would installation of a diplexer mitigate the original question altogether?

 

[SCPD]

The RF tolerability depends on the quality of the Radio

I have a state government vehicle with 3 antennas spaced 43 inches apart. Motorola CDM1550VHF 50 watts Maxrad mlb-5803 wideband antenna in front. (144-160 MHZ) and a 800 mhz 5/8 over 1/2 wave 43 inches away behind that a Maxrad 2m/70cm 1/2 wave/ 2- 5/8wave Antenna with an Icom IC2350 Dual band Mobile in the rear.

The 800 antenna is for a scanner. The bottom line for me is UNIDEN. They can handle it! I had a pro 94 once and POP! the first day! I sold it on ebay for 35.00 describing that it has 3uv sensitivity and was a good nearby 1 system monitor. the buyer was at a California College and wanted to monitor his system only and said that would be perfect! He was happy!

No problems with stuff with good front ends. the Icom and Motorola are 7ft apart with No problems and I have a BCT7 scanning 1 simple 11 channel 800 system, one 4 channel 800 system (conventional style) and 5 VHF and 5 aircraft in the middle. No problems at all.

 

[sflmonitor]

Thanks to everyone that relied. It was very interesting to see all of the various experiences. I think that I will still not operate my 110 watt VHF while my 396xt is on, just to be safe. But it's good to know that some of you haven't had any issues.

 

[Astrak]

The 800 antenna is for a scanner. The bottom line for me is UNIDEN. They can handle it! I had a pro 94 once and POP! the first day!

The PRO94 was made by Uniden.

 

[kb8rvp]

I think the mobile scanners may not be as prone to RF damage but a hand held might be. I have been using a Radio Shack Pro-2096 in the car with a 50 watt VHF radio with no problems for years as well as a Uniden BCD996XT. A friend had a RS Pro-96 hand held with an outside antenna and he damaged the front end and the receive was very poor until he sent it in for service after using it near his mobile VHF radio antenna. I think the mobile scanners have some built in protection that the hand held scanners may not have.

Mike

 

[Para078]

I had a Johnson Duo-Scan zapped by a 50 watt low band at 100 yards. These were prone to that for some reason.

Also put an old 4channel crystal scanner in an ambulance. Antenna was 3 feet from the 5/8 wave high band antenna(150 watts). Put so much RF into the scanner that the tuning resistor(or whatever it was) melted and stuck to the cabinet.