FM radio/military antenna sharing

[86M10086.2L]

I have been doing some research on the subject of using a military radio antenna for a common AM/FM car stereo. I see it is possible to do this with a commercially available CB antenna with simple adapters and coaxial cable. Is there any reason it won't work with a military whip antenna? I know that certain antennas/bases can be tuned to work with CBs. And logic would dictate that if I could do that, it should work with the stereo also (on paper anyway). Is there any reason I can not? Will the ohm value of a military whip be too much for the stereo? If not, are there any antennas or bases that are better suited for this? I would think that the frequency range of a stereo would be well suited for some of these antennas. My M1009 was setup to run two antennas from Uncle Sam. I'm already planning on running a AB-15/AB-558 with MS-116/117/AB-24 for a CB in one spot. And I was planning on putting a dummy antenna, maybe a Singars style (to be period correct) to simply take up the unused spot on the other side of the truck. I have tentative plans of mounting a PRC-77 in the truck later on, and would utilize the second antenna for that also. It would be nice if I could use one for the stereo instead of it just sitting there looking pretty. It would also save me from having to modify my body or fender to mount a stereo antenna. I'm not looking for super range or signal capacity. I would be very happy if it performed as well as a factory setup. Although I would suspect it should do better. Any thoughs would be greatly appreciated.

 

[Wile E. Coyote]

AM/FM broadcast stations are strong enough that you can use a paperclip for an antenna on a car stereo if you wanted to, so for receiving...anything should work. People have used the auxiliary receiver antenna setup on the M151 series (AB-15 and copper whips) for car stereo antennas often in the past...with the only danger I can think of being the..inadvisability...of transmitting at full power on your RT-524 over the back-mounted fiberglass whip while listening to your AM/FM on the long copper AB-15 mounted whip. You'd saturate the front end of the AM/FM at the very least and possibly even cook it.

I've never tried either of the fiberglass whip types for receiving AM/FM broadcast. Ideally your antenna should be resonant for the frequencies you're listening to for max performance, but again - AM/FM broadcast lets you use just about anything because the typical signal strength is so strong.

 

[86M10086.2L]

That's what I thought, my father had a similar sentiment as well. I'm not too big into military radios right now. But I find myself very intrigued by them. So in the future I can see myself at least installing a entry level setup in my truck. If for nothing else than just to play with and for collectors sake. but if can at the very least make an antenna semi functional by means of a car stereo than all the better.

 

[papakb]

My suggestion would be to run your 524 off of one antenna and the stereo on another. Since your truck was configured for 2 antennas anyway that's the way to go. The AB-15/AB-558s will work fine for your stereo for several reasons. As stated above, AM/FM receivers don't care about matching, they're only looking for something to grab the signal out of the ether and with commercial broadcasts at the power levels they are almost anything will do as an antenna. It's when your going after that really low level signal that receiving antennas start to become important.


The tricky part about what your planning will be to get a cable with a PL-259 on one end and a car antenna plug on the other. The coax you use isn't that important so you could probably find one at Radio Shack and then have someone put the pl-259 on the other end for you. Most CB shops could do it for you pretty cheaply.


Kurt
KG6KMJ

 

[cpf240]

What about replacing the windshield with one that has the embedded AM/FM antenna? That is my plan, though me glass is in good shape as it is, so I'm a bit reluctant.

 

[86M10086.2L]

Papakb that's basically my plan. I'm gonna run the CB on one antenna. Then the stereo on the other. I'm planning on making my own radio shelf that will look similar to the GI unit but still allow me to fold my rear seat flat. The GI one does not allow that. Ill mount my future military radio set and CB there. Most likely I'll select a antenna appropriate to what military radio I plan on using in the future. Although it seems most even the broad band ones would be functional for any that I'm looking at. So I may just pick an antenna that would or could have been on the truck while in service. Cpf240 I'm not a huge fan of the window antennas. Although clean looking, they are expensive to replace. Besides one of the reasons I'm doing this install is to eliminate the 8 ugly holes on my quarter panels.

 

[Cleveland Iron]

Car radio coax is 75 ohms, not 50 ohms, but don't let that worry you. Unless you are trying to tune in distant/weak stations you should have no issues. Don't worry about matching. Don't worry about tuning for frequency. Use whatever antenna you like. Yes you will some signal loss with the wrong coax and not having an antenna tuned for the right frequency... ( What is right here anyhow FM is 88 - 108 MHz and AM 540 - 1800 Khz ) So like I was saying... Use whatever antenna you like, run your wire water proof the connections if you can and enjoy your radio. My two meter rig also does AM/FM on the 2 meter antenna. No problems, no worries.

 

[scottgs]

I concur with what's already been said regarding FM broadcast reception on military antennas. It's probably worth pointing out that if you use a MX6707/AS-1729, it would probably be worth setting it to the highest frequency band, which butts right up against the FM broadcast band, and might work especially well. I haven't done this, but it seems to make sense.

However, your performance on the AM band may not be so spectacular with the mentioned configurations. AM broadcast, being much lower in frequency, needs a more appropriatly resonant antenna to work really well. Most quality automotive antennas have an internal loading coil at the base, and special coaxial cable just for this purpose. But, in practice, I bet you'd never know the difference unless you have a habit of listening to weak, distant AM broadcast stations.

Garret
W8BUG

 

[Cleveland Iron]

What he said.