Can I damage my 396 with HAM antennas too close?

[n0xmz]

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.

 

[SAR923]

I don't get it. You say the Larsen antenna in the middle of the trunk is for a scanner. Are going to put in another antenna for the 396? Given the amount of space you have inside the car, why not just pull out the Pro-94 and replace it with the 396? If the 94 hasn't been harmed by the antenna placement, I don't think you'd have to worry about the 396. What it comes down to is there's only so much radio traffic that you can listen to at one time. Another scanner will just add to the din.

 

[slicerwizard]

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?

There's no question that it's possible - just directly connect it via a cable to one of your TX-capable radios and key up. The issue is whether you can couple enough energy between antennas to cause damage. Uniden isn't known for using quality hardware and they don't publish specs that would tell you how much RF the front end can safely handle. Personally, I'd be leery. I lost the front end on my 245 while working for a radio shop (no, I didn't connect it to anything), so it does happen from time to time.

 

[ffexpCP]

All I know is when I key up an 800 XTS2500 (at what-3 or 4 watts?) in the same room as my 396, the scanner looses the control channel of the system. Makes it hard to match new TG IDs with the TG in the radio, but I don't have to worry about feedback then.

I've also had it at a few FM and TV broadcast sites (100W~100KW) while working on the transmitters with no damage.

I've had it skitz out on me but haven't wrecked it yet. At that power level, even our cell phones and our pro gear goes nuts.

 

[af5rn]

Yeah, I've heard stories of guys losing their front end simply by being too close to a transmission tower. Nothing I've experienced or seen personally, but yeah, it's reason for concern.

I solve the problem in my mobile by running the scanners and transceiver off of the same antenna and isolating the scanners with a coaxial relay.

 

[n0xmz]

Thanks for the feedback. To answer Jim's question, I haven't updated the website since installing the Spectra but it's using the 900 MHz Larsen now instead of the Pro-94.

I think I'm gonna put it on the hood, opposite side of the 2m 1/4 wave. I was trying to avoid that but I'd rather have the car look a little goofy than ruin a $500 radio!

 

[slicerwizard]

All I know is when I key up an 800 XTS2500 (at what-3 or 4 watts?) in the same room as my 396, the scanner looses the control channel of the system.

Typical desense / lack of dynamic range.