I did an install for a customer.
The Uniden scanner worked for a while, but is now deaf.
Radios;
Lowband Maratrac, 42-54 (turned down to 60 watts, but maybe running wide open on 6 meters),
Alinco VHF/UHF dual bander.
They are combined on a Maldol tri-band antenna.
The scanner is on a separate 5/8 wave VHF antenna about 3 feet away. (it was working great on lowband).
I am not sure if the Maratrac or Alinco blew the scanner.
Is there anything short of an attenuator that can be put in the scanner coax???
I also may check the power out on the Maratrac on Ham channels, and if high, I could put a VHF antenna on the scanner to reduce coupling....
Scanner blown, RF'd, overloaded. Solutions?
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440roadrunner
- Posts: 236
- Joined: Mon Aug 16, 2004 3:47 pm
I wouldn't be surprised if a moderator removes this post.
Pretty much the only reason that multiple two way co-exists on a vehicle, is that a (good) installer tries to isolate antennas of "close" frequencies to provide some receiver protection, and,
on most legit public service installs, most all vhf will be in one radio, all uhf in another, etc, so that you can either use a dual band coupler to one antenna, which protects the radios from each other, or you can use separate vhf and uhf antennas.
Usually, the detuning of the antennas, and the filters/ tuned circuits in the front ends of the radios will be enough to protect the radios.
Then, you come along with a scanner, wide open front end, with NO protection, .........
I'd think the only way to handle something like this is to provide some sort of antenna switching relay in the scanner's antenna line, activated by any transmitter(s) in the vehicle.
Pretty much the only reason that multiple two way co-exists on a vehicle, is that a (good) installer tries to isolate antennas of "close" frequencies to provide some receiver protection, and,
on most legit public service installs, most all vhf will be in one radio, all uhf in another, etc, so that you can either use a dual band coupler to one antenna, which protects the radios from each other, or you can use separate vhf and uhf antennas.
Usually, the detuning of the antennas, and the filters/ tuned circuits in the front ends of the radios will be enough to protect the radios.
Then, you come along with a scanner, wide open front end, with NO protection, .........
I'd think the only way to handle something like this is to provide some sort of antenna switching relay in the scanner's antenna line, activated by any transmitter(s) in the vehicle.
You might want to look at installing a pair of hot carrier diodes across the input to the pre-amp transistor. This will limit the voltage that can get into the gate of that RF device.
I blew the front end of a GE Delta SX on the VHF band a couple of times. Took replacing the FET the second time to get my attention. Had to drive by a high powered 400 MHz radar each day at work. Finnaly figured out it was the cause of my deaf receiver.
After installing the pair of back to back hot carrier diodes, never had the problem again. The same trick can work on any receiver front end. Just make sure there is some resistor between the diodes and the input of the RF. You may have to add a series resistor in just to help the diodes survive.
Jim
I blew the front end of a GE Delta SX on the VHF band a couple of times. Took replacing the FET the second time to get my attention. Had to drive by a high powered 400 MHz radar each day at work. Finnaly figured out it was the cause of my deaf receiver.
After installing the pair of back to back hot carrier diodes, never had the problem again. The same trick can work on any receiver front end. Just make sure there is some resistor between the diodes and the input of the RF. You may have to add a series resistor in just to help the diodes survive.
Jim
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Birken Vogt
- Posts: 262
- Joined: Thu Nov 10, 2005 7:53 pm
As far as the scanner and two-way in the vehicle, lots of public safety has them around here...fire mucky-mucks, the Forest Service, and just about every Sheriff's car is set up that way. Often I will come across a scanner that is pretty deaf but the users often don't care since it is just a cheap scanner and all they do is listen to other agencies with it, not for vital communications of any type.
Another thing that might work would be a PIN diode across the end of a quarter wave stub on the coax to the scanner, normally conducting, and opens when the transmitter keys, which would then present a short to the scanner recieve line. With all the desense the scanner is not going to hear anything anyway when the other radio is transmitting on the same band
Birken
Another thing that might work would be a PIN diode across the end of a quarter wave stub on the coax to the scanner, normally conducting, and opens when the transmitter keys, which would then present a short to the scanner recieve line. With all the desense the scanner is not going to hear anything anyway when the other radio is transmitting on the same band
Birken
ICE makes a product that is put inline between the scanner and its antenna and also wired to the vehicle's ground. When it detects RF coming in through the scanner antenna, it lights up a red light and supposedly shunts the RF energy to ground.
I bought one of those after blowing the 1N914 diodes in a scanner using a 50 watt mobile radio. I never blew the diodes in the scanner again, however I made sure to shut the scanner off prior to transmitting.
Warren
I bought one of those after blowing the 1N914 diodes in a scanner using a 50 watt mobile radio. I never blew the diodes in the scanner again, however I made sure to shut the scanner off prior to transmitting.
Warren
As far as I am concerned, this topic can stay as it related to the intent of the fourm.
Don't know why that comment would even be made...oh well.
What we did was put as much distance between the antenna's and the scanner antenna's, which worked very well. We had some scanners that worked well with 100 watt x9000's and the new 45 watt XTL5k's. Very rarely have we had to replace a scanner, and it was usually due to age/enviroment (hey, police cars and not the worlds cleanest vehicles and/or operators!).
I have heard of the RF Choaks being used, and usually work ok. I also find that it really depends on what make/model radio and scanner you are using makes a big difference. Some just seem to make scanner chringe more than others.
Using NMO mounts all the way around are a big help too.
Don't know why that comment would even be made...oh well.
What we did was put as much distance between the antenna's and the scanner antenna's, which worked very well. We had some scanners that worked well with 100 watt x9000's and the new 45 watt XTL5k's. Very rarely have we had to replace a scanner, and it was usually due to age/enviroment (hey, police cars and not the worlds cleanest vehicles and/or operators!).
I have heard of the RF Choaks being used, and usually work ok. I also find that it really depends on what make/model radio and scanner you are using makes a big difference. Some just seem to make scanner chringe more than others.
Using NMO mounts all the way around are a big help too.
Lowband radio. The original and non-complicated wide area interoperable communications system
CHP (California Highway Patrol) uses a muting box which is a relay disconnecting/grounding the antenna line of the scanner when the GE Rangr mobile radio PTT line becomes active. This is somewhat easy because they have only one mobile radio with high power, and the PTT line is accessible from either the head or the radio connector.
I don't know what sort of front end design the scanner you are using has. Units such as the Uniden MR-8100 have separate front ends for the various bands, and if just one is blown out you know which radio did the deed. This seems to happen most often on the ones with a FET RF amp as part of the front end as opposed to those that just feed the RF into the mixer without prior amplification.
Some of the old Motracs had a neon lamp across the input to the front end. I at first thought that maybe a pair of back to back diodes across the scanner antenna input would clamp excessive RF input, but they would probably also create a mobile IMD generator as part of the bargain. It sounds like the ICE unit mentioned above might be your answer since it is designed for exactly this problem.
It might be interesting to see how much RF is coming back down the scanner antenna line when the other radios are on the air. In some cases there's enough that you can actually measure it with a wattmeter...
Geoff
I don't know what sort of front end design the scanner you are using has. Units such as the Uniden MR-8100 have separate front ends for the various bands, and if just one is blown out you know which radio did the deed. This seems to happen most often on the ones with a FET RF amp as part of the front end as opposed to those that just feed the RF into the mixer without prior amplification.
Some of the old Motracs had a neon lamp across the input to the front end. I at first thought that maybe a pair of back to back diodes across the scanner antenna input would clamp excessive RF input, but they would probably also create a mobile IMD generator as part of the bargain. It sounds like the ICE unit mentioned above might be your answer since it is designed for exactly this problem.
It might be interesting to see how much RF is coming back down the scanner antenna line when the other radios are on the air. In some cases there's enough that you can actually measure it with a wattmeter...
Geoff
Link/source for ICE?
The ICE unit described in the posts above sound like what I need as I am about to install an X9000 that has been turned down to about 80 watts. A quick Google search did not turn up any links related to the subject.
Here's a link for the product that I bought from ICE: http://www.iceradioproducts.com/reconly.html#rflimiter
Warren
Warren
Warren,
Have you used that ICE unit on a scanner receiving 800 MHz? Their web page indicates the Model 198 Limiter is rated 30-500 MHz, but I'm curious what the insertion loss is around 800 MHz. I send ICE an email, but haven't got a response yet...
I'm glad this thread appeared, as I'm in the process of installing a PRO-2096 scanner in my truck, which already has a VHF and a UHF Spectra in it. I only listen to 800 MHz on the 2096, but my initial test show that the scanner doesn't like it when I key either the VHF or UHF radio, even when it's locked on an 800 MHz system. All three antennas are installed on the roof of the cab.
Have you used that ICE unit on a scanner receiving 800 MHz? Their web page indicates the Model 198 Limiter is rated 30-500 MHz, but I'm curious what the insertion loss is around 800 MHz. I send ICE an email, but haven't got a response yet...
I'm glad this thread appeared, as I'm in the process of installing a PRO-2096 scanner in my truck, which already has a VHF and a UHF Spectra in it. I only listen to 800 MHz on the 2096, but my initial test show that the scanner doesn't like it when I key either the VHF or UHF radio, even when it's locked on an 800 MHz system. All three antennas are installed on the roof of the cab.
Back when I used the ICE unit, the only systems around here were VHF and UHF, and it worked fine on those.
When I blew the diodes in my scanner, an ex Dept. of Public Safety radio tech told me that if I couldn't mount the antennas far enough apart, the best thing to do was to make sure the scanner was shut off before transmitting. I did that, and never had a problem with a scanner again, even with the scanner antenna two feet away from the VHF antenna pushing out 50 watts.
If you hear from ICE, let me know what they say.
Warren
When I blew the diodes in my scanner, an ex Dept. of Public Safety radio tech told me that if I couldn't mount the antennas far enough apart, the best thing to do was to make sure the scanner was shut off before transmitting. I did that, and never had a problem with a scanner again, even with the scanner antenna two feet away from the VHF antenna pushing out 50 watts.
If you hear from ICE, let me know what they say.
Warren
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BikerScout
- Batboard $upporter
- Posts: 177
- Joined: Wed Dec 24, 2003 9:58 pm
OK, I put a watt meter on the scanner antenna.
****I am getting over 20 watts, yes TWENTY !!!****
That is when the lowband Matatrac is in the Ham band, where it is not controllable. When it is in the business band, there is less than half a watt (power set at 60w).
I changed out the 5/8 wave VHF scanner antenna (which worked great on lowband) for a 19 VHF spike.
Now I am getting less than 1/2 a watt on any of the transmitting radios.
I am supprised the scanner worked for a while with that amount of power coming down.
****I am getting over 20 watts, yes TWENTY !!!****
That is when the lowband Matatrac is in the Ham band, where it is not controllable. When it is in the business band, there is less than half a watt (power set at 60w).
I changed out the 5/8 wave VHF scanner antenna (which worked great on lowband) for a 19 VHF spike.
Now I am getting less than 1/2 a watt on any of the transmitting radios.
I am supprised the scanner worked for a while with that amount of power coming down.