WEWN Shortwave Heard on AM

[spunker88]

Hi guys, this one has me puzzled. Of course Im on my analog set so i cant give you exact station freq but I would have to say its at around 540 to 550AM. It was coming in super clear in Upstate NY, I have attached the top of the hour ID which IDs WEWN (EWTN Radio) and gives the shortwave freq.

EWTN has some regular AM affiliates, but none in the 500khz range: http://www.ewtn.com/radio/amfm.htm

Also, when i googled, i found somebody in 2006 picking up EWTN on 540AM:
http://www.hard-core-dx.com/archive/irca/msg12738.html
They thought it may have been WRRD, but that station appears to be an ESPN radio affiliate today.

And even if this was a regular AM affiliate, wouldnt they have to ID themselves at the top of the hour? I am confused...

EDIT: Just to let you know, its still going strong an hour later.

[Robert Grant]

After doing some math, I strongly suspect the station you heard is....

WEWN on 11520 KHz (!)

I've noticed this phenomenon before (not with WEWN in particular), I call it "the image problem you haven't read about".

We all know about the image problem in superheterodyne receivers. Another signal, twice the intermediate frequency above the desired station, (if the oscillator is above the desired station as in nearly all AM BC receivers) or twice the IF below, (if the oscillator is below the desired station).

e.g:

I thought I heard a CBE (1550 Windsor) station on 640. In reality, with my radio tuned to 640, the local oscillator was at 1095 (640+455). A strong signal on 1550 (CBE) mixed with the LO to the IF frequency (1550-1095 = 455), and I was hearing CBE.

Any basic introduction to radio design mentions superheterodyne images on the fundamental carrier.

The "image you haven't read about" is caused by the harmonics of the local oscillator. I noticed it as a child when I found strong 49m (6MHz) shortwave broadcast signals when tuning the near the middle of the AM BCB.

Cheap shortwave radios, when used in urban areas, are also menaced by this problem, especially on the higher frequency bands, from harmonics beating with FM stations (unintelligible, due to wide bandwidth), and, before this past June, video buzzes.

Later, I found it in a "TV sound" radio - variable tuning of both VHF TV bands. On VHF highband, the third harmonic of the LO allowed UHF signals (including unmentionable signals above channel 69!) to get through the system.

In your case, you were probably tuned to either 550.9 kHz (+455=997.9, x 11 = 11065 [eleventh harmonic of LO], + 455, = 11520) or 542.9 kHz (+455=997.9, x 12 = 11975 [twelfth harmonic of LO], - 455, = 11520).

There are two very strong signs a signal you're hearing is a result of this "oscillator harmonic image":
Since the harmonic is a multiple of the fundamental, the effect of your tuning dial is also multiplied. If many signals are tuned in a very small span of the dial, or you need to tune very carefully to hear the station (note that on most radios, you really don't for a station that actually is on 540!) it is probably an image.
Also, the carrier beat (whistle) between a station heard by image, and a station that is actually at the desired frequency, will change if the frequency of the LO is changed (i.e., one moves the tuning dial).

In fact, in your recording, I can hear a heterodyne that is changing in pitch during the recording. This is possibly due to drift in your local oscillator.

Apologies for being so wordy, and good DX!

Rob

[NN2E]

I didn't listen to your sound file. I'm on dial-up and I'd be old by the time I got done downloading it, but...FWIW... RVC 530 KHz, Turks & Caicos, runs religious programming. Not sure if they do EWTN or not. They used to have the frequency all to themselves then, a few years ago, Fidel had to slap one on the same frequency. :-(
73, Ed NN2E
Owner / Operator - Murphy's Law Test Site & Thunderstorm Proving Grounds

[pjdyer]

Ah, LO harmonics on AM BCB radios ... I got a clock radio in late 1965 that also did a wonderful job of picking up 40-m (7-MHz) as well as cw from the 8-MHz maritime band. Since I'd used the latter for cw practice I knew right away what they were. Over a decade later I found that an SX-62 on 30-50 MHz could find local FM broadcast stations via the same route. At least those were tuneable, unlike when the Soviet jammers parked in the 10-MHz region would come thru on the FM i.f. of the 1949 Stewart-Warner after it was activated for that band in 1962 :( No RF amp stage in that old item
http://www.qsl.net/wa5iyx/images/49swsc6.gif

73, Pat - WA5IYX

[spunker88]

After doing some math, I strongly suspect the station you heard is....

WEWN on 11520 KHz (!)

I've noticed this phenomenon before (not with WEWN in particular), I call it "the image problem you haven't read about".

We all know about the image problem in superheterodyne receivers. Another signal, twice the intermediate frequency above the desired station, (if the oscillator is above the desired station as in nearly all AM BC receivers) or twice the IF below, (if the oscillator is below the desired station).

e.g:

I thought I heard a CBE (1550 Windsor) station on 640. In reality, with my radio tuned to 640, the local oscillator was at 1095 (640+455). A strong signal on 1550 (CBE) mixed with the LO to the IF frequency (1550-1095 = 455), and I was hearing CBE.

Any basic introduction to radio design mentions superheterodyne images on the fundamental carrier.

The "image you haven't read about" is caused by the harmonics of the local oscillator. I noticed it as a child when I found strong 49m (6MHz) shortwave broadcast signals when tuning the near the middle of the AM BCB.

Cheap shortwave radios, when used in urban areas, are also menaced by this problem, especially on the higher frequency bands, from harmonics beating with FM stations (unintelligible, due to wide bandwidth), and, before this past June, video buzzes.

Later, I found it in a "TV sound" radio - variable tuning of both VHF TV bands. On VHF highband, the third harmonic of the LO allowed UHF signals (including unmentionable signals above channel 69!) to get through the system.

In your case, you were probably tuned to either 550.9 kHz (+455=997.9, x 11 = 11065 [eleventh harmonic of LO], + 455, = 11520) or 542.9 kHz (+455=997.9, x 12 = 11975 [twelfth harmonic of LO], - 455, = 11520).

There are two very strong signs a signal you're hearing is a result of this "oscillator harmonic image":
Since the harmonic is a multiple of the fundamental, the effect of your tuning dial is also multiplied. If many signals are tuned in a very small span of the dial, or you need to tune very carefully to hear the station (note that on most radios, you really don't for a station that actually is on 540!) it is probably an image.
Also, the carrier beat (whistle) between a station heard by image, and a station that is actually at the desired frequency, will change if the frequency of the LO is changed (i.e., one moves the tuning dial).

In fact, in your recording, I can hear a heterodyne that is changing in pitch during the recording. This is possibly due to drift in your local oscillator.

Apologies for being so wordy, and good DX!

Rob

Its all good, being an engineering student i like to hear the science behind stuff. Given the choices of 542.9 or 550.9 I would probably have to guess 542.9 I forgot to mention that i tried to tune this on my digital display tuner that tunes in increments of 10khz. It couldnt pick up a thing despite the stong, but narrow signal as you mentioned above. Most regular AM signals this stong would be heard on 10 or even 20khz past. Im guessing it was somewhere between 540 and 550 because i couldnt pick it up on my dig display radio at either freq not even faintly. If it was at 550.9 i imagine i would have heard something at 550 on my other receiver even if it was faint.

What are the chances of this happening again? Was this a one night deal or do i have a good change of getting it again using the same radio at the same location?

EDIT: An interesting note, according to EWTN's website the shortwave on 11520khz is actually meant to target Africa/Middle East area but yet is broadcast from Alabama. Does this mean they are incorporating a directional antenna? More evidence that the antennas may be pointing away from USA: http://www.ewtn.com/radio/freq-pop.htm It makes sense due to the fact that shortwave is probably used very little nowadays in the US besides for hobby. So then why such a strong signal in Upstate NY?

Also, here is the WEWN freq chart:
http://www.ewtn.com/radio/freq.htm

[spunker88]

WEWN is back tonight and its on two frequencies. Exactly the same word for word and it has all the harmonics from before, so im going to guess that the signal is being imaged on two frequencies. Its on the same one as before as well as around 630khz. If i manipulate the math above, i get roughly 633.6khz which seems correct on the dial on my radio.
633.6+455=1088.6
1088.6*11=11974.6
11974.6-455=~11520

EDIT: Yea, i would say 633 is about right, WEWN is just slightly past WPRO 630, in fact i can faintly hear WPRO in the background. Luckily WPRO's signal is weak enough that its not overpowering WEWN like a 50kw station would.