Turn On, Tune In, Curse Interference

December 29, 2016 10:51 PM

Help me find benchmark stations on the shortwave bands (5.90 - 10.00 MHz & 11.65 - 18 MHz), so I can figure out how to receive stations with my tiny shortwave receiver. Bonus: I also live 750 meters from a very strong AM station's broadcast antenna, and receive interference from it.

I received a fun present this year: a small shortwave receiver, about the size of a short iPhone. I can definitely hear some faint SW stations here and there, but I get a lot of interference from WMEX AM-1510 in Boston. I tracked down their antenna, and found that I live pretty close by – it's the red blinky light I can see from my kitchen window in the wintertime! Hello WMEX! (They are a right-wing talk station. Michael Savage, etc.) Anyway, I hear WMEX a lot in the 6.0 MHz range, and a few other scattered places on the SW1 and SW2 dials. And I barely hear anything else, at least not near the clarity and strength at which I receive WMEX.

I am an amateur, know squat about electromagnetic wave physics... but I can kludge an antenna from a coat hanger like nobody's business. Given those parameters, can you suggest to me things like:

• what frequencies I should try as tests of reception (I'm near Boston, MA)
• where best to stand in my house in relation to the offending signal
• which appliances I should stay away from while tuning in
• how to boost reception generally, given this is basically a transistor radio with a classic metal extending antenna
• how to keep WMEX from overpowering any signal I get
• and so on.

(In the meantime, I frequently listen to and love the WebSDR here and the directory of other WebSDR's here.)

Thanks!

posted by not_on_display to Technology (8 answers total)

Ham radio operator here; my call is NF3H. I don't do much listening to shortwave broadcasts, so I can't tell you specific times and frequencies to try. However, I may be able to help with some of the other stuff.

In the US, the FCC regulates broadcast transmissions. The regulations include some fairly strict limits on "spurious emissions" (PDF), and these are actually enforced. (Consider also that power emitted off-frequency is wasted money -- it isn't reaching listeners and generating ad revenus.) Thus, it's unlikely that WMEX is actually radiating too much outside of their allocated band. However, the presence of a hugely strong signal at any frequency (other than the one you're trying to receive) makes the job of the receiver much harder.

Things that are likely to improve matters:

• Increase the distance between the receiver and the interfering signal source. (I'm not talking about moving from one room in your house to another -- I mean like double the distance; see if you have better luck the next city over.)
• Use a better, more directional antenna. (A "gain" antenna will receive better in one direction and worse in others, so if you can point it at the signal you want to hear and away from the interference, it can help.)
• Use a bandpass filter to block as much of the interfering signal as possible before it gets to your receiver.
• Use a receiver with better selectivity.

Shortwave listening is unlike listening to local AM/FM broadcasts in a couple of key ways. First, not every station transmits 24/7. Schedule matters! You might hear a strong station one night and it'll be completely gone later. The reason why might be as simple as them not being on the air when you made your second try.

Second, when you listen to a shortwave station that's over the horizon, it is probably via skywave propagation. This is a hugely complicated topic, but the basic deal is the radio waves are bouncing off the ionosphere. The behavior of the ionosphere depends on the so-called space weather, but a key point is that you'll almost always get better reception at night.

That looks like a fun radio, but you're asking it to do a very hard job -- set expectations accordingly.
posted by sourcequench at 11:32 PM on December 29, 2016 [7 favorites]

What he said. I have a handheld Gundig SW radio I listen to outside some nights. Reception varies wildly. Some nights it's full of interesting things; Radio Havana, some sort of Chinese equivalent, way more religious broadcasting than I would have thought possible, counting stations, and some nights I can get absolutely nothing.
posted by bongo_x at 11:43 PM on December 29, 2016 [1 favorite]

It's funny, but I always associate this time of year with shortwave for various personal reasons, related to an 80s Sony ghetto blaster / boombox that for some reason had SW. The number of international broadcasts directed towads North America and Europe has plummeted since then, which makes it hard to know what's listenable.

Anyway, Radio Marti might be a good reference point, broadcast out of Greenville, NC with the aim of being heard in Cuba, but potentially receivable all the way to Canada.
posted by holgate at 11:51 PM on December 29, 2016

Try WWV, which puts out a strong signal on 10.000 and 15.000 MHz (among others). It broadcasts 24/7.

It sends the same message on all frequencies. By comparing them, you can get a good idea of ionospheric conditions and decide what bands will be coming in strongly that day.

If you don't hear WWV at all, you're gonna have a bad time. It's much easier to receive than most other stations you'd care about, because it's transmitted at a very high power and its messages are easy to recognize. Even a portable radio with a telescopic antenna ought to be able to pick it up.

Once you're receiving WWV, proceed by following the others' excellent advice.
posted by edlinfan at 12:07 AM on December 30, 2016 [4 favorites]

Not in your area, so I don't know your "benchmark" stations would be - around here I'd just say "Radio Australia" (at least until the end of January) or "Radio China International"- but ditto what sourcequench said.

Unfortunately that radio doesn't seem to have an external antenna socket, which makes points 2, 3, & 4 tricky - connecting an antenna that's directional & balanced (more to 'null out' the interfering station than increase the signal of the wanted sw station) and tuned (to act as a bandpass filter & improve selectivity) will require a bit of work. It's not difficult (a suitable antenna, a balun to match the balanced antenna to the unbalanced 'whip', and a bit of thought on how to connect it) - but it's probably a step beyond what a complete beginner who just wants to hear stuff on their new radio wants to do ;).

(If you do go that way, I'm a big fan of electrically small loops e.g. 30cm-1m diameter. But I'll let you investigate those if you choose...)

Which leaves sourcequench's first point - get away from the interfering/overloading source. Hop in your car one afternoon, and drive to a park or open area a few miles from any big transmitters. Spend a couple of hours before & after sunset scanning the bands, & you'll probably find something interesting...

(And check out http://www.shortwaveschedule.com. Handy for figuring out what you might be hearing, and giving you ideas of stations to chase!)
posted by Pinback at 12:21 AM on December 30, 2016

The other thing is that, that close, it's quite likely that much of the interference from your local AM station is getting into the radio not via the antenna but directly into the receiver circuitry. Not much you can do about that apart from (a) move away, or (b) shield it completely & use an appropriate external antenna.

Either way it's not only interfering by popping up all over the dial, but also by desensitising the radio in general. Hopefully you'll get a nice surprise and a better idea of what you might receive once you get out from under it, even temporarily.
posted by Pinback at 12:33 AM on December 30, 2016

Response by poster: Hey, thanks, everyone. Your answers confirmed my suspicions, and gave me a refresher in what little I did know about signals to begin with.

In any case, I will try the suggestions in this thread. I cannot pick a best answer because they're all great; however, my first try will be taking it to the middle of Vermont when I see my sweetie for New Year's Eve.

I also vaguely remember in high school physics, my teacher talking about how frequencies will echo themselves on other frequencies due to the math of the sine-waves of the signal, which is why you can sometimes hear, e.g., a radio station's ghost signal a couple of MHz or KHz up or down the dial. This have anything to do with that, you think? (Not that it matters; I think your answers are all much more reliable and make more sense than that, especially considering the strength and that the frequencies are wayyy in another area of the dial, and that these aren't "ghost" signals but MICHAEL SAVAGE AT ELEVEN VOLUME.)

One other thought: because I was having a similar problem earlier in the year – I could barely record music on my iMac cause the input was picking up WMEX. Someone in the thread (in Mefi Music) suggested a ferrite core to wrap around the guitar cord. It did the trick fairly well. Is there a similar product I could use (or did I miss clicking a link upthread)? E.g., is there a reliable, cheap bandpass filter that I could buy?

an 80s Sony ghetto blaster / boombox that for some reason had SW

I had a Hitachi boombox that had a few different bands on it, and a manual dial (never mind the two-cassette dubbing!), and I would just listen to shortwave for hours and hours after sunset. I noticed that when I placed my hand on the antenna, I could pick even more stations up. It kept me up for hours and hours, late into the night when I should have been sleeping or BBS'ing.

(Sidenote: That boombox lasted for decades, and I would later record my band's live performances with it. I found out that Sean Lennon (whom my band played a couple of shows with when he was in Cibo Matto) had the same exact boombox when he was growing up, and we bonded talking about it – dubbing, and the shortwave thing.)

Thanks again, everyone.
posted by not_on_display at 11:27 AM on December 30, 2016 [1 favorite]

Given the state of the radio business in the US, I wouldn't doubt that the station itself is maladjusted (most are..they rarely have staff engineers these days, just someone on call for when it totally breaks), but even if it weren't you'd still be screwed without at least a good notch filter on the antenna input to filter it out.

I bet there is a local ham group that could help with ideas about getting decent reception in that sort of radio environment. Many of them are drawn to that sort of challenge, after all.
posted by wierdo at 2:25 PM on December 31, 2016