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Author Topic: Holy moley!  (Read 12272 times)
W7GIF
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Posts: 122




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« on: June 13, 2013, 09:16:47 PM »

Tonight between 03:30 and 04:00 on 9790, China Radio International in Beijing was 115 to 120db over S9 (on 3 receivers). Nothing else even close to that on 31m. It was almost as though my feedine was tied directly into theirs. Gotta wonder how much power they're actually pumping. Or, maybe I should check the back yard to se if there's a monster antenna that got installed (quietly) overnight.
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K0OD
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Posts: 2520




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« Reply #1 on: June 13, 2013, 11:03:45 PM »

Quote
China Radio International in Beijing was 115 to 120db over S9 (on 3 receivers)

What receiver's S-meter reads to 120 dB over 9? What is that, something like a million times more power than S-9 plus 60 dB?
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W7GIF
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Posts: 122




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« Reply #2 on: June 13, 2013, 11:36:30 PM »

Quote
China Radio International in Beijing was 115 to 120db over S9 (on 3 receivers)

What receiver's S-meter reads to 120 dB over 9? What is that, something like a million times more power than S-9 plus 60 dB?
Well, first I have to backtrack on my claim of +120 db. That was the observed measurement from the HRO-500, BUT, it's the TOTAL signal level...not the figure over an S9.
I was just going to revise my claim when I saw your reply. It was actually +80 to +85 over S9. All 3 of the receiver's meters are calibrated to between +40 over to +50 over S9, and max RF attenuation of 30 to 40 db available. I had max attenuation cranked into all three, and the S-meters were still on or near the peg. The three receivers are HRO-500, RA-17c3, and FT-ONE.
My apologies for the original mis-statement of signal strength. Guess I should have just stated that CRI was so strong that 40db of RF attenuation wasn't sufficient to pull the needle off the peg of meters calibrated to +40 to +50 over S9.......while all other heard 31m signals were below (unattenuated) S-9. THAT was actually the point of my original (flawed) post.

BTW, I think my math is right: 85 db over S9 represents a signal voltage of just over 16,400 times greater in magnitude than an S9 signal. At any rate, it's one helluva strong signal. And I can't venture an explanation for why CRI was significantly much stronger than any other signals at that time.....except to say that current prop conditions are very weird and unpredictable.
« Last Edit: June 14, 2013, 12:07:36 AM by W7GIF » Logged
NK7Z
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Posts: 711


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« Reply #3 on: June 14, 2013, 07:36:40 AM »

Quote
China Radio International in Beijing was 115 to 120db over S9 (on 3 receivers)

What receiver's S-meter reads to 120 dB over 9? What is that, something like a million times more power than S-9 plus 60 dB?
Well, first I have to backtrack on my claim of +120 db. That was the observed measurement from the HRO-500, BUT, it's the TOTAL signal level...not the figure over an S9.
I was just going to revise my claim when I saw your reply. It was actually +80 to +85 over S9. All 3 of the receiver's meters are calibrated to between +40 over to +50 over S9, and max RF attenuation of 30 to 40 db available. I had max attenuation cranked into all three, and the S-meters were still on or near the peg. The three receivers are HRO-500, RA-17c3, and FT-ONE.
My apologies for the original mis-statement of signal strength. Guess I should have just stated that CRI was so strong that 40db of RF attenuation wasn't sufficient to pull the needle off the peg of meters calibrated to +40 to +50 over S9.......while all other heard 31m signals were below (unattenuated) S-9. THAT was actually the point of my original (flawed) post.

BTW, I think my math is right: 85 db over S9 represents a signal voltage of just over 16,400 times greater in magnitude than an S9 signal. At any rate, it's one helluva strong signal. And I can't venture an explanation for why CRI was significantly much stronger than any other signals at that time.....except to say that current prop conditions are very weird and unpredictable.
Put a tuned circuit in front of a diode and light and you can have a CRI indicator lamp for when they are transmitting!  Smiley
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Thanks,
Dave
For reviews and setups see: http://www.nk7z.net
W7GIF
Member

Posts: 122




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« Reply #4 on: June 15, 2013, 10:56:39 AM »

Yeah, just getting back into SWL'ing after a long absence, I've discovered some new sources of info on the web. Seems that CRI transmits on 9790 out of Havana, and that goes a long way toward explaining their signal here in Arizona. But, even so, given their signal compared to others from the Caribbean, their Havana transmitter must be pushing some serious power.

Having a good time resurrecting old boat anchor receivers for SWL'ing, and listening to international broadcasts. And, even though the bands are sparsely populated compared to forty years ago, it's still fun and interesting.....and informative.

Happy listening....
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K5TED
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Posts: 679




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« Reply #5 on: June 15, 2013, 11:07:51 AM »

Glen Hauser says...

"9790, May 27 at 0454, CRI relay is still on with huge unmodulated carrier,
causing desensitization on the FRG-7 out to plus/minus 35 kHz or so. This thing
must be aimed right at us with 250 kW and high-gain curtain."
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KE7TMA
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Posts: 446




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« Reply #6 on: June 15, 2013, 10:07:34 PM »

Quote
China Radio International in Beijing was 115 to 120db over S9 (on 3 receivers)

What receiver's S-meter reads to 120 dB over 9? What is that, something like a million times more power than S-9 plus 60 dB?

If your radio has an attenuator and a good linear RF gain control it is quite possible to measure signals which would normally be off the scale.
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W7GIF
Member

Posts: 122




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« Reply #7 on: June 20, 2013, 04:28:24 PM »

Quote
China Radio International in Beijing was 115 to 120db over S9 (on 3 receivers)

What receiver's S-meter reads to 120 dB over 9? What is that, something like a million times more power than S-9 plus 60 dB?
Well, first I have to backtrack on my claim of +120 db. That was the observed measurement from the HRO-500, BUT, it's the TOTAL signal level...not the figure over an S9.
I was just going to revise my claim when I saw your reply. It was actually +80 to +85 over S9. Guess I should have just stated that CRI was so strong that 40db of RF attenuation wasn't sufficient to pull the needle off the peg of meters calibrated to +40 to +50 over S9.......while all other heard 31m signals were below (unattenuated) S-9. THAT was actually the point of my original (flawed) post.
Well, CRI's English broadcast on 9790 at 03:30 to 04:00 is down to it's more usual signal level of +35 to +40 over S9 here. Guess I'll abandon thoughts of designing a 9790 trap...for now.
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KB4QAA
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Posts: 2245




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« Reply #8 on: June 25, 2013, 12:31:50 PM »

I recall reading that CRI was leasing time on a SW station stateside, Texas?, last year.  That might account for the high signal levels.
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G7MRV
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Posts: 465


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« Reply #9 on: June 25, 2013, 01:11:30 PM »

Most of the 'International' broadcasters use leased relays around the world, rather than attempt to hit their desired target audience from home territory. The Vatican state lease out a big transmitter site, as do the BBC (Balfour Beatty facilities).

A few years ago I had a nightmare of a problem in that at my QTH in northern England, Radio Korea was breaking through on my powered but otherwise out of use PC speakers! This drove me mad until I discovered their service was being relayed out of Rampisham!

These days, as far as broadcasting goes, the accountants shout louder than the propagandists! Wink
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