Low-band AM/FM antenna replacement

Anderegg · #1 (**permalink**) 03-03-2013, 8:15 AM

I recently installed a Motorola Maxtrac low-band radio into my vehicle to monitor the Highway Patrol. I needed a low-band antenna that wouldn't make my car look ridiculous with a huge 5 foot NMO whip on the roof! I tried to order a Sti-Co covert AM/FM direct replacement unit, but either no one could get Sti-Co to return their calls/emails for a quote, or they just spit out a $320+ figure out of their price sheets.

I ended up simply unplugging my stock car stereo antenna, and running an extension cable to my Motorola and putting a mini-UHF tip on it. It works "OK", and was basically a FREE install option, but it could definitively use improvement. I have a 2003 Honda CR-V, and I am looking to find a replacement whip that will screw into my fender antenna hole. I could acquire a Japanese model whip, which would be cut for the Japanese FM band that begins at 76MHz as opposed to 87MHz that mine is tuned to. This would offer a slight improvement, as it would be closer to the 39MHz frequencies I am trying to monitor, but I want better. A gooogle search found that some countries in eastern Europe use the OIRT FM band, which starts 65MHz. How would i find out if Honda makes an antenna for this band for my vehicle, so I could just buy one cheap and screw it in?

That would be the easiest and cheapest route I think, but I am exploring the option of mating my 39MHz tuned NMO antenna whip to the screw in base of my stock antenna.......I am not sure how to go about doing that as I am unaware of how soldering or welding receiving element parts would affect performance. Any ideas or suggestions?

Paul

mm · #2 (**permalink**) 03-03-2013, 9:30 AM

You can connect a MFJ-903 antenna tuner between that maxtrac and the Honda FM antenna and it should match close to 42 MHz. The 903 is for 50-54 MHz but the tuning range will extend down to 40 MHz.

LtDoc · #3 (**permalink**) 03-03-2013, 10:13 AM

I think changing to an antenna such as those you suggested would be a waste of effort. Sure, there would be some improvement, maybe, but not enough to be significant. 'Fractional' improvements are just exactly that, fractional. If you know someone who has one, try one of those 'huge' 5 - 6 foot antennas on a mag-mount for a day or two, just to see the differences. I would think you would hear some differences, but they won't be 'huge'. Selecting an antenna because of 'looks' only affects the 'looks', very, very seldom (if ever) will it ever do anything beneficial for it's electrical properties.
- 'Doc

Anderegg · #4 (**permalink**) 03-04-2013, 3:31 AM

I have a 40MHz NMO with mag mount that I have used in the past, but it stands out way too much, and is an eye-sore. In testing, the AM/FM antenna receives somewhere between a 1/4 wave VHF high and the 5 foot low band whip. The AM/FM antenna doesnt receive as well as the full size whip, but it doesn't require it's own mount, and receives better than the 1/4 VHF-H that does.

It works for now, but I think I want to put the low band whip on the AM/FM screw stud.....any ideas where I can find information on correctly doing this?

Also, I don't transmit on this antenna, and I don't need it hooked up to my stereo, I have a CD/DVD/SD/USB for any music needs. :-)

Paul

W8RMH · #5 (**permalink**) 03-04-2013, 4:14 AM

The Antenna Farm has a lot of mounting options - Mobile Antenna Mounts at The Antenna Farm

mmckenna · #6 (**permalink**) 03-04-2013, 6:06 AM

Have you considered mounting the antenna on the front fender, opposite the am/fm antenna? I've done this with NMO CB whips in the past. The FM antenna you are suggesting isn't likely going to be any different than the one you have, they are not usually tuned antennas.

Other option, if you are not going to transmit is to split the am/fm antenna to allow it to feed both, or try to find some of the tape used for the "hidden" in glass antennas that some auto manufacturers use for an am/fm antenna rather than an external whip. Foil alarm tape works also.

Anderegg · #7 (**permalink**) 03-26-2013, 11:59 PM

I found a temporary solution, as well as a "final solution".......

I went to the hardware store and bought a stainless steel threaded stud that fits into the stock AM/FM antenna hole on the fender. I then bought some small clamps, and basically put the Larsen whip next to the stud, and clamped them together. I now have a 39 MHz whip where my AM/FM antenna used to be. The clamps are small, but a bit ugly. I also bought a larger threaded stud that fits into the base of the stock Larsen NMO mount, and will be searching for a machine shop to tap and thread this to accept the top of the AM/FM stud. I assume stainless steel presents no problem to a radio signal? The larger stud appears to be gold in color, possibly brass.......wonder how that would affect reception?

Paul

mmckenna · #8 (**permalink**) 03-27-2013, 12:22 AM

Stainless steel won't be an issue. Larsen makes NMO mounts that are stainless.
The existing AM/FM antenna stud is likely brass. What you need to be concerned about is the issues with the dissimilar metals and moisture causing corrosion. That can be easily addressed by periodic cleaning and inspection.

Sounds like a neat set up.