30khz - 450khz... Why can't I pick anything up?

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redchord11

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Hey all,

It's been a great 2 months with my IC R75 hooked up to my RF Sys passive antenna. It's not even properly rigged - but I've been picking up some great stuff here and there. I have a question.

Why is it that from 30 khz - approx 450khz I can't pick anything up? I hear that "machine gun" like sound throughout this entire span. I usually tune in at night to this end of the spectrum as recommended. I tried using the filters but nothing comes through. Is this just electrical interference?

Right after 450khz the normal local AM brodcasts come through as clear as a bell. Any ideas on what I'm doing wrong / possible suggestions?

PS I live in an urban part of NY- about 20 min from NYC.

Thanks, this is such a helpful forum.
 
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ka3jjz

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That area of the spectrum has very few broadcasters in it. There are a few European and Asian folks there, but they're not easily heard during this season. Most of the time, you will see them reported in the winter and early spring. The number of these are growing fewer and fewer as local FM (and to some extent, satellite services) take their place.

There are experimenters, airport beacons and other things in this band. The broadcasters you are hearing starting from 450khz is, no doubt, a product of overloading. Nothing you are doing wrong here.

Generally speaking, efficient antennas here include various forms of loops, loaded towers (yes it can be done - I've been to one or two beacon stations that use this technique) and, for some at least, really long wires (and I do mean LONG). I'm not entirely sure if that RF Systems antenna would be resonant all the way to 30 khz (which is where submarines transmit, although it's highly unlikely you'd be able to demodulate it...) but you're not missing much in any case. The LongWave Club of America has been involved in this field for a great many years. Do a search on the name if you are interested. 73 Mike

[edit] Looking at the Universal website, the RF Systems PRO series is resonant down that far (although very expensively!). But the others generally aren't.
 
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zz0468

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Your best bet is a loop antenna. You can buy ready made antenna, or you could build something. The vast majority of what you hear will be beacon stations on the 200-500 KHz range. A couple of good places to listen to test your receive capability are WWVB on 60 KHz, and at 100 KHz, which is LORAN. WWVB is just a carrier pulsing up and down in signal strength, LORAN is a pulsed noise that sounds like a motorboat. If you're hearing those, you should be hearing other stuff.

Keep in mind, except for a very small handful of things, the stuff you hear will be very weak. In fact, I use a program called Spectran just to see things. You may be in a better position to hear the European broadcasters - here in California, we don't get those much at all, so there is absolutely NO voice traffic to listen to.
 

ka3jjz

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zz, it seems to me that you might have a better shot at some of the Russian (and maybe Chinese) LWBC stations, if they are still on the air. I seem to remember there were a couple from Moscow, Kiev and maybe Petropavlosvsk. But yeah, they would be tough no matter if you were on the West Coast or not. I seem to recall there were some Japanese ones as well, although they may have since migrated.

73 Mike
 

zz0468

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I would have thought so too, but I've never heard any.I'm not sure there are any still on the air. I HAVE managed to catch the Russian, Japanese, and Chinese standard frequency stations operating between 40 KHz and 100 KHz, so I know the path exists at times - just no broadcasters. Yet.
 

redchord11

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That area of the spectrum has very few broadcasters in it. There are a few European and Asian folks there, but they're not easily heard during this season. Most of the time, you will see them reported in the winter and early spring. The number of these are growing fewer and fewer as local FM (and to some extent, satellite services) take their place.

There are experimenters, airport beacons and other things in this band. The broadcasters you are hearing starting from 450khz is, no doubt, a product of overloading. Nothing you are doing wrong here.

Generally speaking, efficient antennas here include various forms of loops, loaded towers (yes it can be done - I've been to one or two beacon stations that use this technique) and, for some at least, really long wires (and I do mean LONG). I'm not entirely sure if that RF Systems antenna would be resonant all the way to 30 khz (which is where submarines transmit, although it's highly unlikely you'd be able to demodulate it...) but you're not missing much in any case. The LongWave Club of America has been involved in this field for a great many years. Do a search on the name if you are interested. 73 Mike

[edit] Looking at the Universal website, the RF Systems PRO series is resonant down that far (although very expensively!). But the others generally aren't.
Oh, ok well thanks for clearing that up. I was under the impression that there was more going on on these frequencies. I might look into setting up a loop though. See if I get anything different going on.
 

StereoScout

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Oh, ok well thanks for clearing that up. I was under the impression that there was more going on on these frequencies. I might look into setting up a loop though. See if I get anything different going on.
There were many stations to listen to in that band until last year 2007. The FAA & FCC decommissioned that band of aviation communications. (Turned it off.) Now that band is mostly abandoned.
 

N1BHH

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About 10-15 years ago, I had a 750 foot wire only about 8 feet off the ground. I came across a roll of #22 silver, multi strand, teflon jacketted that was very rugged. I used it from 100 kilohertz to around 10 Megahertz for just about anything I could hear. I just walked out through the woods and pushed the spool over branches I could reach over. I end fed it out of a 120 foot buried piece of RG6/U that a friend had left over from doing cable television drop installations.

Where the coax came out of the ground on the edge of the woods, I had a couple 4 foot ground rods driven into the moist soil. The property next door to where I lived was once all swamp and was filled in, but had good ground conductivity. I also had some leftover #12 stranded copper that I poked into the ground to provide more contact with the soil. This antenna played very well. I could hear Medium Wave broadcast stations that went off air at sunset in the Central and Mountain time zones on a regular basis. The antenna served me well, until I moved out. This antenna was very low noise. When 75 meters was full of static, I used it as a receive antenna and heard everyone cleanly. I took it down and gave it to someone else, who made a few dipoles with it.
 

zz0468

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There were many stations to listen to in that band until last year 2007. The FAA & FCC decommissioned that band of aviation communications. (Turned it off.) Now that band is mostly abandoned.
This is untrue. Yes, the FAA is gradually removing NDB's from service, but there are still HUNDREDS of them on the air, and the FAA's actions have no impact on the marine beacons that still occupy the band. BTW, the NDB's are getting replaced with DGPS reference stations, which are every bit as interesting to listen to.

The band is quite active, on a good nights listening, I can hear 30-50 stations across most of the U.S.
 

VernM

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No one has touched on the fact that few receivers have anywhere the sensitivity at the Low F range that they do above the broadcast band. A pre-amp, such as Polimar used to make (and may still make) specifically for VLF is a must if you want to find things there.

There are US Navy VLF CW sigals there too, occasionally, and the amateur LowFer experimenters.
 

prcguy

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The noise is so high on VLF that it dominates the S/N rather than the receiver noise figure and a preamp will not help unless your using a very small loop or a clip lead for an antenna. Preamps for VLF can also get blitzed by strong AM broadcast. There are some good active antennas that have very high level FETS that don't overload easily and the active portion is more for impedance matching rather than gain. A great VLF antenna you can make is the AMRAD, cost about $75 in parts and plans can be found here:
http://www.arrl.org/tis/info/pdf/0109031.pdf
prcguy
No one has touched on the fact that few receivers have anywhere the sensitivity at the Low F range that they do above the broadcast band. A pre-amp, such as Polimar used to make (and may still make) specifically for VLF is a must if you want to find things there.

There are US Navy VLF CW sigals there too, occasionally, and the amateur LowFer experimenters.
 

ka3jjz

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This is untrue. Yes, the FAA is gradually removing NDB's from service, but there are still HUNDREDS of them on the air, and the FAA's actions have no impact on the marine beacons that still occupy the band. BTW, the NDB's are getting replaced with DGPS reference stations, which are every bit as interesting to listen to.

The band is quite active, on a good nights listening, I can hear 30-50 stations across most of the U.S.
And to add to the DGPS comment - these can be decoded. I'm pretty sure SkySweeper does it, and so does this...

http://www.coaa.co.uk/dscdecoder.htm

73 Mike
 

k9rzz

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I've had best luck with an EWE antenna. Low noise. The band here in the midwest is FULL of aero NDB beacons 24/7. No problem - always DX to chase. Broadcasters from EU and AF are _RARE_ here.
 
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