HFU HF Underground
Technical Topics => Equipment => Topic started by: Looking-Glass on December 09, 2018, 0927 UTC
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Does any one know of a HF gen coverage receiver or amateur transceiver that goes as low as 20KHz or even 10KHz would be even better?
Preferably something recent/modern.
All my gear cuts out at 30KHz...except for the FT-2000D where I use the 10KHz receive clarifier to get down to 20KHz... ;)
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As I recall, the R71 will go down to 10KHz either by tricking the tuner, or using one of the replacement rom boards. A selective voltmeter might be a easier piece of gear to get that tunes down there without funky programming or replacing roms.
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The AOR AR7030 goes all the way down to well below 10kHz.
Noel.
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It's said that the lower you can tune your rig is directly proportional how well the engineers regarded the cleanliness of their local oscillator.
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I think the RX-340 goes down that far. Mine seems to anyway.
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As far as radios that are not insanely expensive/hard to get. The Rycom 6040 selective voltmeter is a good choice. I think it goes down to less than 10 Kc, and up to a few Mc. it has a frequency counter as the freq. display, and digital automatic frequency control, so its about as stable as a synthesized rig and as easy to read. they turn up on eBay fairly often for between $200 and $1000. Of course, earlier models without a digital readout can often be cheaper. I used to have a Rycom 3121A, which had a dial rather than a readout. My first NDB was heard with that radio.
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My Kenwood TS-2000X will dial down there as well. It initially stops at 30kHz, but the RX RIT can dial down an addition -20kHz so that you can end up at 10kHz. If this rig does this, then I suspect that the TS-590, TS-480, TS-570, TS-990, and other Kenwood rigs could probably do this too, and no modifications required.
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I also Forgot to mention Demodulators. These can be hard to find unless you search them specifically, because 'Radio' often is not in the title. The receiver I use is a WJ DMS-105a-2 Watkins Johnson demodulator. You probably won't find one of those, but there are others. Being designed for subcarrier listening on microwave baseband channels, many are not very sensitive, and need an external preamp, but they pretty much all will tune as low as 4 kilocycles, as this is the first channel in an FDM telephone cable. Mine (and many others) will tune to 1000 Hz or even slightly lower. Modern amenities are not to hard to find either as many demodulators are either digitally controlled, or fully software defined.
P.S, if you want to use a computer for the low end stuff, there is no better source of info than this site,
http://www.vlf.it/
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Most interesting!
Str.
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I also Forgot to mention Demodulators. These can be hard to find unless you search them specifically, because 'Radio' often is not in the title. The receiver I use is a WJ DMS-105a-2 Watkins Johnson demodulator. You probably won't find one of those, but there are others. Being designed for subcarrier listening on microwave baseband channels, many are not very sensitive, and need an external preamp, but they pretty much all will tune as low as 4 kilocycles, as this is the first channel in an FDM telephone cable. Mine (and many others) will tune to 1000 Hz or even slightly lower. Modern amenities are not to hard to find either as many demodulators are either digitally controlled, or fully software defined.
P.S, if you want to use a computer for the low end stuff, there is no better source of info than this site,
http://www.vlf.it/
Oops, forgot our pc's have soundcards that can listen down there, just need an antenna, some software, and you're all set.
http://www.vlf.it/pernter1/x-fi_modifications.html
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The FT-2000D base radio goes down as far as 20KHz with the introduction of the Receiver Clarifier, however, I also notice with the big Yaesu that receiver sensitivity also drops dramatically below 40KHz, unlike the small Icom IC R-75 which holds it's own.
Will look at the AOR AR7030 when I have time over the weekend, thanks for that, also will look and see what a RX-340 is too...thank you people.
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If you use an active antenna or antenna preamplifier the low sensitivity may not be a problem, many such receivers just have a 6dB/octave roloff below a certain frequency, or a transformer that is designed to be lossy at lower frequencies to prevent overloading from static or broadcasts. the performance and selectivity should not suffer as long as you can get enough signal into the receiver.
There are also modifications listed online for many rigs, and improving LF performance may be as simple as removing an RC circuit or winding a new transformer, I however, understand if you would want to modify n expensive new radio. not so sure I would either.
(I have this problem, where I modify things that work perfectly and break them, most of my repair skills came from repairing stuff I broke)
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Also, possibly someone still makes converters that shift the vlf up to say 10MHz or wherever. These might offer improved performance as they're designed for the band in question but transvert the sigs where a hf receiver will be at peak performance.
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My WJ 8718 will tune down to 5khz I think the Racal will too
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The wj8718, 8716 and 8718-a don't all say they will go that low, but they probably will. My 8718 specifies 500 KHz as the bottom end, but will tune down to 15 or so
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Also, possibly someone still makes converters that shift the vlf up to say 10MHz or wherever. These might offer improved performance as they're designed for the band in question but transvert the sigs where a hf receiver will be at peak performance.
That would be my vote too.
You can make your own up converter for this range; you just need a DC-coupled mixer, a variable LO, probably a few amplifiers and baluns as a quick and dirty bare bones solution. Op-amps make great amplifiers at LF. :)
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Yeah, just make sure you use opamps rated for hifi audio as run of the mill opamps like the 741 are great noise sources.
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The Analog Devices AD797 is a fantastic choice for LF and VLF preamps.
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Also, possibly someone still makes converters that shift the vlf up to say 10MHz or wherever. These might offer improved performance as they're designed for the band in question but transvert the sigs where a hf receiver will be at peak performance.
That would be my vote too.
You can make your own up converter for this range; you just need a DC-coupled mixer, a variable LO, probably a few amplifiers and baluns as a quick and dirty bare bones solution. Op-amps make great amplifiers at LF. :)
Someone, Palomar I think, used to make one that had a xtal osc and a nice diode mixer, translated the entire band to 3 or 10mhz or wherever it was. It's front end was designed to pass vlf and reduce anything higher. Wish I had one, my pro2 is a might deef down there.
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Yeah, just make sure you use opamps rated for hifi audio as run of the mill opamps like the 741 are great noise sources.
The 741 is very, very old and quite noisy. The AD797 is newer ( and still ~20 years old) but (as ThElectriCat mentions) is well-known for low-noise performance and reasonable distortion characteristics. 10 MHz gain-bandwidth product fits the bill here.
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Someone, Palomar I think, used to make one that had a xtal osc and a nice diode mixer, translated the entire band to 3 or 10mhz or wherever it was. It's front end was designed to pass vlf and reduce anything higher.
Yes, I remember that Palomar Engineers carried one back in the 80s and 90s, back when they had red lettering (or was it red cases?) on everything.
Maybe you can find one of these converters on Ebay.
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Hamcrafters (K1EL) has sold a Palomar copy in the past. Their web site indicates they may bring it back.
A more sophisticated VLF/LF converter is here:
https://www.herostechnology.co.uk/pages/VLF-LF-MF_Up-Converter.html
It is more expensive of course.
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https://www.herostechnology.co.uk/pages/VLF-LF-MF_Up-Converter.html
They have some neat stuff!
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Maybe this isnt what you are looking for, but if you look long enough on ebay you can find a preamplifier for a lock in. These are usually made by stanford research or princeton applied research (eg&g PARc).
These often have a 1 to 10 MEGohm full differential input, and will really bring a rather VLF deaf receiver to life, as in many cases the poor performance of some receivers in that range is just because of their lack of sensitivity.
Beware bandwidth limitations though, some of these have an upper frequency of a kilohertz or less. many, however, will go up to a couple hundred kilohertz.
PS. there are also transimpedance models that have near zero input impedance, and a gain between 10 KV per amp or 1GV per amp. these are good for loops
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Maybe this isnt what you are looking for, but if you look long enough on ebay you can find a preamplifier for a lock in. These are usually made by stanford research or princeton applied research (eg&g PARc).
These often have a 1 to 10 MEGohm full differential input, and will really bring a rather VLF deaf receiver to life, as in many cases the poor performance of some receivers in that range is just because of their lack of sensitivity.
Beware bandwidth limitations though, some of these have an upper frequency of a kilohertz or less. many, however, will go up to a couple hundred kilohertz.
PS. there are also transimpedance models that have near zero input impedance, and a gain between 10 KV per amp or 1GV per amp. these are good for loops
Having one or more of these is arguably bragable.
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Hamcrafters (K1EL) has sold a Palomar copy in the past. Their web site indicates they may bring it back.
K1EL posted an update (with a picture) of the replacement for the Palomar VLF converter they will be selling:
https://www.hamcrafters2.com/VLFX.html
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If you don't want to spend the big money on a Watkins Johnson and government/military receivers like that, and don't mind an older design, I've been using a Bearcat DX-1000 for years. It receives very well down to 10 kHz with excellent sensitivity below 2 MHz unlike most other consumer receivers. They can be found on eBay for around $100-150 because of some bad reviews (from SWLs) and I use it with a ferrite loopstick for finding those submarine signals down to 15 kHz with no problem.
Another, albeit more pricey, receiver is the Sony CRF-1. This one tunes and receives literally down to 0 kHz. They can be found occasionally but anywhere from $600 (which is what I paid for mine) to over $1000. For that much money, might as well save up for a WJ/Racal/Cubic.
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If you don't want to spend the big money on a Watkins Johnson and government/military receivers like that, and don't mind an older design, I've been using a Bearcat DX-1000 for years.
This is where selective level meters can really shine, if you are ok with an analog dial. my rycom 3121 was 120 dollars shipped. I haven't personally played with the Bearcat DX-1000, but other some even cheaper radios, can preform well in the right condition. I have a tecsun PL-880, and although it only goes down to 100 khz, I was surprised how good it can be if one is careful to not overload the front end. I bet there are many receivers out there that can do well with careful use.
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K1EL has abandoned efforts to revive the Palomar VLF converter.
https://www.hamcrafters2.com/VLFX.html
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I get very good results with several of my SDRs down in this region, I think I've posted screenshots of waterfalls if the various VLF submarine communication transmitters I've received. That's probably the lowest effort / best bang for your buck. Plus now you have a modern SDR radio ;D