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Author Topic: Can I damage a scanner with other antennas nearby?  (Read 682 times)
N0XMZ
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« on: June 18, 2008, 09:28:20 PM »

I'm looking for a place to mount a new antenna on my car for the new scanner when I'm driving. I'm using a Uniden BCD396T and I don't want to damage this expensive toy by exposing it to too much RF. Is that even possible, I wonder?

Well here goes. There's not much room on the trunk, which is where I'd like to put it. I already have an HF Workman (Hamstick clone) antenna on a ball mount on the rear passenger quarter-panel that transmits (at most) about 100 watts. On the other side of the car is a trunk-lip mount Larsen 2/70. Estimated ERP is 60 watts at 146, 50 watts on 440. In between the two is a Larsen 902-928 MHz antenna. Estimate ERP on it is 50 watts.

The Larsen 2/70 and the Workman HF antennas are connected to an IC-706MK2G and the 900 MHz Larsen is connected to Motorola Spectra.

If I throw in an 800 MHz Motorola antenna for the scanner, can I expect anything more than possible desensing? What if I use a bigger antenna such as Rat Shack's mobile scanner antenna (mag mount replaced with NMO, of course).

I already have a 2m 1/4-wave on the hood that runs APRS at 30 watts and it desenses/overloads the 706 on 2 meters every time it beacons but it's also about 7+ feet away. You can see pics of all these antennas on my website, www.n0xmz.com. There's also a GPS receiver on the trunk but I'm not too worried about it.

As a last resort, I will explore putting one or more antennas on the roof. The problem with that is the moonroof but I suppose I can mount one or two behind it.

Hopefully, I'm worried about nothing.
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K0BG
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« Reply #1 on: June 19, 2008, 05:10:47 AM »

In most cases, it takes a lot of RF to blow a front end, even on a scanner. About all you're going to get is a lot of desensing.  I suggest you use the opposite side of the hood, but then I haven't seen photos of the set up.

Alan, KØBG
www.k0bg.com
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N8EKT
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« Reply #2 on: June 19, 2008, 08:19:42 AM »

Yes you can burn the first rf amplifier stage out of your scanner in your situation.
Vertical separation and distance from transmitting antennas is your only hope.
If you can bumper mount the scanner antenna, you will likely obtain both the vertical separation advantage as well as sheet metal shielding from the other antenna patterns.
It could be better to use your front bumper vs. the back but getting that antenna out of the radiation plane of the others is critical.
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W3LK
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« Reply #3 on: June 19, 2008, 02:17:42 PM »

If I were in your situation, I'd try one of the low-profile patch antennas for the scanner and mount it as far forward on the roof as I could or use simply an 800 mHz 1/4 wave whip. I would NOT use a RS scanner antenna, no matter how it is mounted.

I seriously doubt you are going to blow the front end on the scanner if the separation is four feet or more, but anything is possible. Separation is your friend, in this case. Smiley

Good luck with the installation.

73,

Lon - W3LK
Naugatuck, Connecticut
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AA4PB
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« Reply #4 on: June 19, 2008, 03:29:54 PM »

Anything is possilbe, but damaging the scanner is not very likely at those power levels. The more separation the better.
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KC2JFS
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« Reply #5 on: June 20, 2008, 09:22:24 AM »

You should send an email to Uniden and ask this question. I would be curious to see the response.
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N0XMZ
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« Reply #6 on: June 23, 2008, 10:15:23 AM »

Thanks for all the feedback. I think I will mount it on the hood, opposite side from the APRS antenna.
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G3YPQ
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« Reply #7 on: July 24, 2008, 10:07:55 AM »

Yes I believe I just did. UBC72xlt connected to a vertical on one side of the car and Mobile rig to one on the other. Now, I cant be sure the set was switched on, it probably was, but a QSO on 2m killed the Uniden. Now dead, wont switch on, nothing. Tried taking the batteries out and discharching the supply. but total deadness. beware!
Phil
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