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Author Topic: General Coverage Comms rxer down to 20KHz?  (Read 1472 times)

Offline KaySeeks

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Re: General Coverage Comms rxer down to 20KHz?
« Reply #15 on: January 03, 2019, 0701 UTC »
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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Offline Josh

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Re: General Coverage Comms rxer down to 20KHz?
« Reply #16 on: January 03, 2019, 2121 UTC »
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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Offline ThElectriCat

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Re: General Coverage Comms rxer down to 20KHz?
« Reply #17 on: January 03, 2019, 2204 UTC »
The Analog Devices AD797 is a fantastic choice for LF and VLF preamps.
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Offline Josh

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Re: General Coverage Comms rxer down to 20KHz?
« Reply #18 on: January 03, 2019, 2218 UTC »
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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Offline KaySeeks

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Re: General Coverage Comms rxer down to 20KHz?
« Reply #19 on: January 04, 2019, 0256 UTC »
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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Offline KaySeeks

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Re: General Coverage Comms rxer down to 20KHz?
« Reply #20 on: January 04, 2019, 0300 UTC »
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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Offline NJQA

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Re: General Coverage Comms rxer down to 20KHz?
« Reply #21 on: January 04, 2019, 1218 UTC »
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.


Offline KaySeeks

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Offline ThElectriCat

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Re: General Coverage Comms rxer down to 20KHz?
« Reply #23 on: January 05, 2019, 0253 UTC »
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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Offline Josh

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Re: General Coverage Comms rxer down to 20KHz?
« Reply #24 on: January 05, 2019, 1932 UTC »
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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Offline NJQA

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Re: General Coverage Comms rxer down to 20KHz?
« Reply #25 on: January 14, 2019, 0003 UTC »
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


Offline pjxii

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Re: General Coverage Comms rxer down to 20KHz?
« Reply #26 on: January 17, 2019, 0133 UTC »
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.

Offline ThElectriCat

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Re: General Coverage Comms rxer down to 20KHz?
« Reply #27 on: January 18, 2019, 0259 UTC »
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. 
In another life, I could have been a telephone engineer.