External AM radio antenna ideas

[VinceAtReal4x4's]

I know this is a somewhat odd idea but I feel like having good AM reception is paramount for me in remote areas. It keeps me entertained late at night when I can't sleep, I can get news and the biggest reason is I can hear weird stories on the "Coast to Coast" radio show! I'm often camped out deep into Mojave for example, and would like to pick up 720AM out of Vegas or 640 from LA but I usually end up catching some skip from NY or San Fran that of course, fades in and out like crazy.

Issue is using a shortwave/AM inside a metal rig really limits reception possibilities. Any other Hams (or radio geeks) out there have an idea on how I could get AM boosted with an external antenna? I can go through my wall to run a cable to my ext. input on my shortwave radio I have sitting beside my bed area. I don't want to run a shortwave wire to a tree or anything if I can avoid that step. Wondering if there is some kind of AM range coil antenna rated for outdoor use that might work? This is the only thing I've seen that seems legit but was hoping for something more of just an antenna. https://www.ccrane.com/item/ant_am_twin/101105/twin_coil_ferritereg;_am_antenna_signal_booster

 

[unusedusername]

Getting good AM broadcast reception in a vehicle is a tricky thing.

First, here is the physics. Radio waves have a length. This length is dependent on the frequency at which the radio wave is transmitted. The length of an efficient transmission or receive antenna is also dependent on the length of the radio frequency you are trying to receive. Most ham rigs use antennas that are between 1/4 through 5/8's wavelength. AM broadcast radio transmits in the band between 176 meters and 555 meters, meaning a efficient quarter wave vertical antenna would be between 44 and 139 meters tall. Obviously, this isn't practical on a vehicle.

You can make an antenna regain some efficiency when it is shorter by using tricks with coils, specific lengths of the coax cable between the antenna and the receiver, and making the antenna out of very precise materials at very specific lengths. Auto manufacturers hire a RF engineer to design the system on each car so that the vehicles get as good of performance as possible. Most of this tuning happens on the antenna side, allowing multiple vehicles in their lineup to use the same head units.

The aftermarket does not have this level of per-vehicle engineering. It's very unlikely that you'll get as good of performance as the stock radio with anything aftermarket. A handheld or table top radio sitting in the vehicle will be even worse then something designed to be integrated into a vehicle.

That being said, any outside antenna will work better then any inside antenna. If your radio shows the receive strength meter then you may see an additional 1-2 S units by going to an outside antenna. You could connect one of these (link) to your radio's antenna input, mount it on the side of the vehicle, and get the correct coax connector cables. if you are not moving, you can put up a long (maybe 100 foot) wire antenna, like these (link), in a tree while camping to get much better reception then anything that will fit in a vehicle.

 

[DaveInDenver]

@unusedusername, if you're talking about traditional bee stinger or whip antennas I don't think a great deal of effort was expended optimizing them for MW AM broadcast. They seem to rely mostly on being swamped with high received signal strength along with a great deal of RF gain.

The whip on my 2008 Tacoma gave no indication of being an inductor tuned for 300m wavelengths anyway. So the extent to which they work or not doesn't have much to do with a critical length or electrical equivalence as it does just having some reasonable length of conductive material exposed to the ether to be excited.

Then figure cars the past few years have ditched bee stingers and fender whips in favor of active antennas in the shark fins that probably are electrically resonant coils in the medium wavelength AM band along with FM, GPS and cell data. Those aren't easily swapped for an aftermarket option anyway.

But in this case I'm not sure he's asking about his car radio but maybe a dedicated table top radio. In that case I'd suggest researching what the SWL DX people do. That means shortwave listening (SWL) for distance (DX) for Google purposes. Many authorities and countries are turning off their government SW, MW and HF propaganda stations so it's not something that's done as often anymore but I think people still try to listen to commercial and "special interest" stations just as being asked here, so the principles still apply.

I can't say I know anything about that C.Crane device but I have seen MFJ makes a SW/MW/HF tunable active amp that seems similar and from what I understand does help dig out weak signals and reduce interference. Having two antennas in the C.Crane device might mean it's doing some sort of diversity reception, which probably can't hurt with fade.

https://www.mfjenterprises.com/Product.php?productid=MFJ-1020C

Ultimately, though, there's really no substitute for stringing up as much wire as you can practically hang and getting it tuned to your frequency of interest. Searching for "long wire antennas" and "tuners" or "couplers" might lead you down some paths for ideas.

http://www.hard-core-dx.com/nordicdx/antenna/lab/coupler.html

 

[prerunner1982]

A ham radio HF antenna on the outside should at least help, though not optimal.
Maybe a 75m hamstick and a Wolf River Coils Silver bullet 1000 would get you about as tuned as you are going to get with a "short" vertical antenna (relative to a long wire antenna tuned to the AM frequencies)
Any large external antenna will likely be better than the telescopic antennas on the radio.