PDA

View Full Version : Tunable Lowfer/LF Receivers and You



KG4CGC
12-29-2009, 12:10 AM
Anyone monitor VLF/LF? (LW)?
What equipment did you use?
What wisdom can you depart amongst us?

Thank you for your time.

kf0rt
12-29-2009, 08:38 AM
Long time ago (60's and early 70's), I used to listen to a weather station on LF using an old Knight-Kit Star Roamer. This was below 300KHz and I gathered at the time that it existed to provide weather to pilots. Marine use made more sense to me at those frequencies, but there's not a lot of that in the mountain time zone and the weather reports always had places like Chadron, Nebraska and they always included the cloud ceiling. Last I listened down there, the band was dead, so the weather station must have gone the way of some other technology.

More recently, did a little looking into the system behind the "atomic" clocks and watches that you can buy; the ones that automatically stay in sync with the NIST clock. This is all done at 60KHz using a VERY low bitrate by "power modulating" the transmitter. That is, they indicate the mark-space stuff by raising and lowering the transmitter power output. The odd thing is that, while I have a couple devices that USE this (and they do work), I'm unable to hear the signal on an IC-7000. You would think that a reasonably sensitive receiver would pick up a carrier when a $30 watch has no problem. (Must be something I'm missing).

Anyway, here's an interesting (fairly technical) paper on the whole atomic clock thing:
http://tf.nist.gov/general/pdf/1877.pdf

HUGH
12-29-2009, 01:56 PM
Just setting up for 136kHz here with the intention of applying for 500kHz which is available on request. I have a Kenwood R5000 with all the filters and made a tuner for 136kHz to block strong adjacent signals. Reception should be on one of a pair of frame antennas and transmission on a long wire. That's where the fun will really start!
In progress at this moment is a 2-vxco mixer to generate 136-138 kHz and I have collected some IGBTs for power.

KG4CGC
12-29-2009, 03:47 PM
Thanks and thanks.
Part of the question deals with the fact that although the average ham rig will tune down pretty low, they are deaf and in the case of an FT100, you just hear the internal oscillator.
So where do you go for a tunable receiving device. I already have the kit mentioned in another thread and as soon as I've tested that out I'll let you know what I think.
http://jacksonharbor.home.att.net/lfconv.htm

kf0rt
12-29-2009, 03:58 PM
I've been meaning to check into the AM BCB attenuation in the IC-7K. As I recall, they attenuate that band by 20db or something (but it can be turned off?) -- explains KOA being S8. Could be the attenuation starts at 1.6MHz and works to the lower limits of the rig.

The converter looks like a fun project. What do you expect to hear?

KG4CGC
12-29-2009, 04:04 PM
Aside from the usual stateside stuff, I want to hear LWBCB from everything to the east of me.

KG4CGC
12-29-2009, 08:45 PM
Just heard about trying a Selective Level Meter. What is it and how would I use it?

N8YX
12-30-2009, 03:59 PM
Look at getting an old marine receiver. Most will cover down to 10KHz and have a preselector built in:

http://www.qsl.net/n/n4xy//Images/Electronics/Ham_Radio/Receivers/rcvr_itt-mackay-marine_3031a.jpg

A Harris RF-590, Collins HF-2050 or Racal 6790 is also a good choice.

You can often find the Mackay receivers available on the surplus market. I paid $650 for a 3031A and $550 for a 3030AR, which is a thumbwheel-tuned version of the 3031.

Both work extremely well for pulling in signals in the LF/MF region of the spectrum.

Neither has a noise blanker, but an outboard DSP unit takes care of that.

Unless you have a lot of room for a Beverage antenna, you'll probably want to utilize a magnetic-loop arrangement for purposes of noise cancellation.

Here's a page with a wealth of information on them:

http://www.nitehawk.com/rasmit/ws1_21.html

KG4CGC
12-30-2009, 04:34 PM
Nice link. :) Thanks.

XE1/N5AL
01-03-2010, 02:05 AM
Just heard about trying a Selective Level Meter. What is it and how would I use it?

Some suggested reading:

"Frequency Selective Voltmeters and their Uses in the Radio Hobby", by Don Moman
http://www.qru.de/selective%20level%20meters.html

"Off-the-air Frequency Measurement and the HP3586B Selective Voltmeter", by Jack Smith, K8ZOA
http://www.cliftonlaboratories.com/off- ... troduction (http://www.cliftonlaboratories.com/off-the-air_frequency_measurement.htm#Introduction)

"A Practical Guide for Using the HP 3586 A/B/C Selective Level Meter", by Bill Feldmann, N6PY
http://www.k7jrl.com/pub/manuals/hp/358 ... 20V2.0.pdf (http://www.k7jrl.com/pub/manuals/hp/3586/HP%203586%20OPERATING%20GUIDE%20V2.0.pdf)

The Hewlett Packard 3586A, 3586B and 3586C units show up on eBay all the time. With luck, you can get one for less than $100 USD, but they are heavy and it might cost an additional $50 USD to ship it.

N2NH
01-03-2010, 02:10 AM
Kewl. I didn't know there was actual equipment you could buy to XMIT for LowFER freqs.

Here's the Wiki on the Lowfer Band 160Hz to 190Hz (1750 Meters). I've known about the secondary allocation on this band and the fact that no license is needed since college. My friend and I were going to set up a legal Phone broadcast station there in the early 1970s. Much like the European LW broadcasters. We even contacted the FCC about it. They reluctantly agreed that there was nothing in the rules (then) that said phone wasn't allowed. They were even more reluctant to admit that most stations there used a fixed frequency. ;)

Money, a lack of affordable equipment and a really wacked out old coot (who had the lone patent then for some of the equipment we needed) taught us this was not a prudent avenue of pirate radio.

http://en.wikipedia.org/wiki/LowFER

As far as listening, I used a SONY ICF-2001 with some success back in the early 80s. All stations on the band were beacons sending Morse. If I remember right, I had no trouble picking up Halifax and Boston. Sometimes I'd get Gander.

N2NH
01-03-2010, 04:25 AM
Here's a site I came across for LFDX

http://www.lwca.org/

http://www.lwca.org/sitepage/part15/index.htm

I believe the 185Hz station used to be the "Boston" station.

122.5 is still Halifax HERE: http://www.beaconworld.org.uk/files/lfguide.pdf

KG4CGC
01-03-2010, 10:23 AM
Thanks for furthering the infos.
Now John, did you mean Hertz, or KiloHertz?

N2NH
01-03-2010, 06:52 PM
Thanks for furthering the infos.
Now John, did you mean Hertz, or KiloHertz?

KILO Hertz. Ever since I dropped soda on this "waterproof" keyboard, I've been dropping first letters everywhere.
:lol:

N4VGB
01-04-2010, 11:50 PM
Just heard about trying a Selective Level Meter. What is it and how would I use it?



Just heard about trying a Selective Level Meter. What is it and how would I use it?

Some suggested reading:

"Frequency Selective Voltmeters and their Uses in the Radio Hobby", by Don Moman
http://www.qru.de/selective%20level%20meters.html

"Off-the-air Frequency Measurement and the HP3586B Selective Voltmeter", by Jack Smith, K8ZOA
http://www.cliftonlaboratories.com/off- ... troduction (http://www.cliftonlaboratories.com/off-the-air_frequency_measurement.htm#Introduction)

"A Practical Guide for Using the HP 3586 A/B/C Selective Level Meter", by Bill Feldmann, N6PY
http://www.k7jrl.com/pub/manuals/hp/358 ... 20V2.0.pdf (http://www.k7jrl.com/pub/manuals/hp/3586/HP%203586%20OPERATING%20GUIDE%20V2.0.pdf)

The Hewlett Packard 3586A, 3586B and 3586C units show up on eBay all the time. With luck, you can get one for less than $100 USD, but they are heavy and it might cost an additional $50 USD to ship it.

If you've never worked with a frequency selective voltmeter before, it might be exasperating trying to use one for a VLF rcvr. Since they were designed as test equipment, they don't feature AGC/AVC, noise canceling circuits, etc., all manual control is the name of the game with them.

Some of them don't have enough front end gain to be used as an off the air rcvr, so a preamp might be necessary with those sets.

All of them will work as VLF rcvrs, but you must remember that was not their intended use and mods may be necessary for your particular use. My personal choice would be Sierra or Rohde & Swarz units.

KG4CGC
01-05-2010, 12:35 AM
I'm not sure the AgC/AvC would be of concern once the noise was blocked out. The front end may be helped with a pretuner for the antenna considering that an antenna resonant at 3 mHz would be nothing more than a capacitor.

If there is more to this I would like to hear more. I am aware of the considerations involved in using a piece of test equipment. I understand that Rycom made a unit that was practically a radio back when the level of manmade noise was not an issue.

N4VGB
01-05-2010, 02:03 AM
I'm not sure the AgC/AvC would be of concern once the noise was blocked out. The front end may be helped with a pretuner for the antenna considering that an antenna resonant at 3 mHz would be nothing more than a capacitor.

If there is more to this I would like to hear more. I am aware of the considerations involved in using a piece of test equipment. I understand that Rycom made a unit that was practically a radio back when the level of manmade noise was not an issue.

The old Rycom stuff that I have here is tube, not solid state, but they are very usable as rcvrs. The newer Rycom stuff is usually fairly high priced when in good condition and still working up to spec.

I used a multi turn loop turnstile antenna to null out as much noise as possible. It's still mounted in the attic of my old home on one of those cheapy Rat Shack rotators.

VLF was interesting for a while, then my interest faded and I haven't fooled with it for probably 20 years now. It gets really noisy down there very low, how low are you wanting to go?

W9WLS
01-05-2010, 08:13 AM
40 some odd years ago while still attached to the military, I had some exposure to a VLF installation South West of Colo.Springs.
The Rx/Tx equipment was actually in "THE" mountain but the antenna"FIELD" was in the basin just West of Ft.Carson , the antennas were "drilled" in to the basin to a depth of 600 feet (or thereabouts) , the Rx/Tx gear was a mix of Raython / Racal and Collins / Rockwell, don't remember exactly what the rx sensitivity was but the tx power was in the mega-watts.
The "story" I got was that the installation was used to communicate with submarines and "other" shore based installations around the country .
If memory serves (don't bet on that) there were similar facility's outside of San De ago (sp?) , some where near the Great Lakes Naval Academy, one on the South Carolina coast , the Texas Gulf coast and one in Hawaii (which would make sense) where all else , I'm not sure but it would be a safe bet that if we were doing it so were the Russians .
"If" such facility's are still in operation I'm sure they have been "upgraded" to solid state and most likely digital by now .
That's about all the history I can give you for now (at least on list), hope it gives you something to think about, some of the old equipment may be on a surplus list somewhere but I could not tell you where to begin to look and I really don't remember any "nomenclatures" so no help there.
73, John

WTKX
01-05-2010, 08:37 AM
http://spaceweather.com/glossary/inspire.html

http://www.smeter.net/stations/vlf-stations.php

N4VGB
01-05-2010, 08:10 PM
Have you considered one of the SDR pieces for VLF work???

Maybe not the cheapest approach, but a lot of bang for the bucks invested.

KG4CGC
01-05-2010, 08:25 PM
I need an example of a piece that would work there.

N4VGB
01-05-2010, 10:37 PM
I need an example of a piece that would work there.

RFSpace SDR-IQ, Perseus, Quicksilver QS1R and the list goes on forever. SDR pieces are springing up like weeds in your yard, they're everywhere now.

A Google search for SDR receivers will keep you busy shopping a long time.

Most of the SDR pieces will receive down to 10-15 kc just fine.

WARNING!!! Panoramic and waterfall RF displays are severely addicting, once viewed, you're hooked.

KG4CGC
01-05-2010, 11:44 PM
Bit of an overload looking for sdr that way.

This is nice: http://websdr.ewi.utwente.nl:8901/

N4VGB
01-06-2010, 12:49 AM
Bit of an overload looking for sdr that way.

This is nice: http://websdr.ewi.utwente.nl:8901/

Well, you could start off slow, the SoftRock lineup is good for that. Nice little kits, dirt cheap, great little performers. Nothing like winding toroids about the size of a Cheerio and soldering SMDs the size of an ant. :lol:

Or you could go on the SoftRock Yahoo Group and there you'll find some guys who will build the SoftRock kits for you about as dirt cheaply as KB9YIG/Tony Parks sells the things.

The SoftRock lineup is definitely the cheapest and easiest way to investigate SDR. Then proceed from that point onward and upward.

KG4CGC
01-06-2010, 01:44 AM
Saw his page. Nearly sold out of everything. http://www.kb9yig.com/
That's fine. I have enough to solder for a few days. Need to expand the work area.

N4VGB
01-06-2010, 02:44 PM
http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... K:MEWAX:IT (http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=270509358293&ssPageName=STRK:MEWAX:IT)


Here ya go barkeep, VLF made easy. Collins R-389, still a mechanical and electrical marvel, since it receives right through it's own IF range with no problem. Sneaky little IF shift going on to accomplish that feat.

KG4CGC
01-06-2010, 04:52 PM
Well, it's not from radio-mart soooooo, No Sale!

N4VGB
01-06-2010, 06:49 PM
Well, it's not from radio-mart soooooo, No Sale!

:rofl: :rofl: :rofl:

One of Martyn's loyal customers eh!?

:rofl: :rofl: :rofl:

KG4CGC
01-06-2010, 10:54 PM
Changing out a transformer AC line filter capacitor should be no biggie, right? Other than making sure it is discharged.

N4VGB
01-07-2010, 12:19 AM
Changing out a transformer AC line filter capacitor should be no biggie, right? Other than making sure it is discharged.

:chin: I don't really know what a "transformer AC line filter capacitor" might be??? :think