The AM Forum

I’ve noticed an interesting phenomenon here today around  2:25 p.m.  I was tuning around the lower half of the 80 meter band to see how much that portion was in use.  I spotted only one CW station around 3515 kHz.  But then I noticed a weak AM signal at 3630 kHz.  In less than a minute it slowly faded completely away.  Canadian AM’ers I wondered?

It hit me that the guy sounded like Rush Limbaugh.  I got out the calculator thinking that I was probably hearing a harmonic of a broadcast station.  Well, 3630/2 is 160 meters, but then 3630/3 = 1210 kHz. WPHT which is a Philadelphia area station.  I tuned to 1210 and there was Rush!

So I’m hearing the 3d harmonic of 1210 kHz. but the level varies quite a bit.  I wonder if it's just due to the ionospheric propagation variations or perhaps due to an airplane flying near the towers.  The transmitter site is about 40.0 miles from me (after checking the FCC database and a great circle distance calculator).  I’ve never spotted their 3rd harmonic on 80 meters before.  They are 50 kW, non-directional.

After monitoring for a while, I have heard the station signal rise up again and fade away several times.  It seems more likely to be due to sky-wave propagation of the 3rd harmonic.

When I lived near  Albany, NY I could hear up to the 5th harmonic of WGY  (fund. on 810 KC).  This was about 20 miles from the station. Somedays , I could only hear the 2nd...   This is the "proof"  for too much time available.

When one thinks 'bote it, a 50KW broadcash output gunna have a few watts of harmonics, and the antennas have a gud ground plane...  There was a guy who usta load up an broadcast AM tower and get on 80 metros...  a while back...   klc

Not being a broadcast engineer, I'm wondering what the FCC spec on the third harmonic might be?
Assuming they are 50kw (I can hear them up here near Catskill NY no problem, often during the day as well, or maybe all the time during the day...) then what's the effective power of the third harmonic?  ::)

      _-_-WBear2GCR

What is Rush's callsign. Maybe he doesn't know the band isn't open for phone down there yet. Was he talking with Bacon and George???

I didn't listen long enough to determine who Rush was talking with.  Of course he doesn't need anyone to talk with.

Yes, it is a tough situation when you are running high power.  I can probably hear an 80 meter signal at 40 miies with less than 100 milliwatts AM.  They are 50 kW, non-directional.  We are asking for at least 60 dB attenuation of the 3rd harmonic, to not hear them.  In all of 50 years in the Philadelphia area, I never noticed their signal on 3630 before.

I have some broadcast signals come and go on 160 meters also. 

This is all a fact of radio life.

Funniest post of the week.

Maybe he was talking to Irb, since Irb doesn't get on 3885 anymore.

I've heard several 2nd and 3rd harmonics from BC stations when I lived in Baltimore. Never checked for any of the locals since moving to the present location.

Tom, It is also quite possible in these conditions recently to be hearing hams from this side of the pond as we in England have two AM frequencies around this area used often, those being 3.615 and 3.625, there are nets on Saturdays at 08.00 GMT onwards till about 10.00 also in the evenings and day during the week on these frequencies. Hams here often using transmitters such as T-1509 and WS-53 etc, these sets quite capable of reaching the US in favourable conditions. This morning on the AM net on 3.615 we were joined by a few European stations including one from Germany who was a good 5/8 signal. a distance of roughly 450 miles across land so maybe possible over the sea to reach much more. It is also possible in the UK to hear, but not read, many US AM stations on 75m 3885 or thereabouts. 73 Max M0GHQ

Maybe 3615 and 3625 would be two good frequencies to keep an ear on, throughout the evening hours until about 0800 GMT, after the 15th of December.

Interesting on the German AM stations.  Didn't someone post a message here recently saying that Germany has enacted a bandwidth limit on all phone signals that limits the total bandwidth to that of SSB?

There has been a 6.0 kHz bandwidth limit in Canada for decades but I have yet to hear of a Canadian AM'er being busted for exceeding it.  Maybe that's the situation in Germany, too.

A European-wide bandwidth limit wouldn't surprise me though, since the EU is notorious for coming up with all kinds of absurd regulations and petty restrictions.  EU bureaucrats even told French cheesemakers that they could no longer make many of their world-famous cheeses the traditional way, because that would be in violation of new health regulations.

As for AM broadcast harmonics, I remember when I worked as CE of a 1kw daytimer, we had a 2nd harmonic that was clearly audible all the way across town.  The boss assured me that it still fell within the FCC's limits, and the outside engineering firm that did our annual proofs never indicated anything to the contrary.