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Best mobile antenna to replace this kind of mount?

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#1
Is there a unique name / identifier for this kind of factory installed antenna mount, normally used for typical AM/FM radio?

Are there drop-in replacements for this kind of antenna mount that will provide an antenna more suitable to the frequency range for a radio scanner (e.g. Uniden BCT-15)?




I do not want to add additional antennas. I want something to replace this single antenna as a "stealth" antenna.

This is an eighth generation Toyota Corolla (E110).

(All photos in this post are licensed as Creative Commons Attribution Share-Alike (CC-BY-SA).)
 
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#2
Hey there. Use an AM/FM car antenna coupler. It's a little adapter that connects to both your am/fm radio and scanner, thus allowing am/fm and scanner reception (without interference)! Your car antenna will be used for both am/fm and scanner reception, so no additional antennas needed. Band coverage is 25-1000MHz. I have a BCT-15 installed in my car, and I didn't want to bother with additional antennas. Got myself this handy little coupler from scannerworld.com and it works like a charm. Don't get these radio couplers from ebay because those probably suck. Get it from scannerworld.com They only go for about $18.00. I've had my scanner and radio on at the same time, and no interference whatsoever.

http://www.scannerworld.com/content/product/model/ANT63BNC
 
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#3
I tried exactly that unbalanced coupler with unsatisfactory results. If you look inside, it's just a 47pF ceramic disc capacitor inline with the BNC-terminated lead intended for the scanner, and a 2ohm* resistor inline with the Motorola-terminated lead intended for the head unit.

*If I'm reading the color code correctly: red, black, black, gold, brown, on a blue colored resistor.

I read somewhere in a longer discussion of whether unbalanced couplers were really as terrible as popular impression suggests, and one comment recommended with emphasis to use a combiner, not a coupler. So I sprung for the SP-1300 combiner/splitter from ScannerMaster. (You can read about my install here.) Perhaps it's the placebo effect of spending $40, but the results seemed much better over that of the coupler... but the end result is still only as good (in my estimation) as the telescoping antenna that's included with the BCT-15.

...which is why I asked about a replacement antenna better suited to scanning. I'm already using the factory car antenna.
 

SAR923

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#4
I think the problem is the orientation of your antenna. Since commercial AM-FM stations radiate horizontally polarized signals, having an antenna almost laying on your roof isn't bad. What you're trying to get on your scanner are vertically polarized signals. An antenna that's almost horizontal is never going to work well on those signals. I'd just add a small scanner antenna like the Larsen 150/400/800 to the trunk lip and you'll get much better reception. If you really don't wan't to add another antenna to the outside of the car, just get a suction cup mount for the inside of the window and attach a good rubber duck like the Diamond RH-77.
 
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#5
I think the problem is the orientation of your antenna. Since commercial AM-FM stations radiate horizontally polarized signals, having an antenna almost laying on your roof isn't bad. What you're trying to get on your scanner are vertically polarized signals. An antenna that's almost horizontal is never going to work well on those signals. I'd just add a small scanner antenna like the Larsen 150/400/800 to the trunk lip and you'll get much better reception. If you really don't wan't to add another antenna to the outside of the car, just get a suction cup mount for the inside of the window and attach a good rubber duck like the Diamond RH-77.
Thanks so much for your response. Here's what I've figured out:

The Antenna Farm has NMO specialty mounts including the Maxrad MPM26 pivot mount NMO:


They also sell the Larsen tri-band NMO150-400-800 (in black) that you (and many others) suggest.
(Although a runner-up is apparently the Maxrad BMAXSCAN1000 - "B" for black, vs. chrome.)


Now, the pillars on my car would allow a 3/4" hole (such as with an Antenex HS34 hole cutter:


and the inside trim panel for the pillar provides direct access to the pillar metal frame, so I could run the RG-58 wire behind the glovebox (coming from the passenger's side pillar) to the scanner radio in the center console ISO 7736 / DIN slot.

This way I don't have to drill through the firewall of the engine or worry about antenna wires having kinks crimped in them by a trunk or hood. And the black finish will look like it was factory installed.
 

SAR923

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#6
Seems like a well thought out plan to me. With the exception of putting the antenna in the center of your roof, you should get about as good a reception as you're going to get. We used those Larson antennas on our patrol cars for years and they were very durable and performed well. They replaced the huge A/S MON3 antennas we had previously and, except for low band, they actually worked better...and broke off a lot less often. :)
 
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