Re: LF: Re: VLF Stability and soundcard locking

[M0FMT <m0fmt@yahoo.co.uk>]

Mal.....  for my ten cents worth.

 

Without being able to add modulation or on-off keying then no QSO is taking place.

 

I suppose you could say if there is a carrier then some one is in the shack but that's not really a QSO.

 

I was hoping at the start of this exercise that a CW or other PSK or similar real time QSO could be carried out over say 10/20kms. From the tests Chris G3XIZ has done the best looks like a real time QSO would only happen over a 1.5km path cross town.

 

Academically these tests are very interesting but I don't think IMHO they are advancing Amateur Radio Communications. It will be limited to a very select number of enthusiasts who are set up to TX and RX this type of transmission. However I will continue to try and pick up Chris 11kms away. It will help me understand how to make a sensitive receiver (something I need badly)

 

73 es GL Pete M0FMT IO91UX

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From: mal hamilton <g3kevmal@talktalk.net>
To: rsgb_lf_group@blacksheep.org
Sent: Wed, 9 March, 2011 15:55:12
Subject: LF: Re: VLF Stability and soundcard locking

I agree with these comments, and have said it before.

If all radio amateurs on all the other bands used this system of uh bandwidths and day long qso's Amateur Radio would cease as a hobby.

The aim should be to generate enough ERP so that a qso could take place in a reasonably short time and be observed by others in say QRS 3 - 60. SWL listeners/viewers could also particpate.

The Dreamers band will fizzle out if transmitted signals are not improved so that a larger audience can engage in the activities. 

also who is going to buy a PCM2900 or similar gadgets for a ONE OFF QSO if you are lucky.

Again QSL reports on frequency alone are not VALID - it could be any carrier.

G3KEV

 

 

----- Original Message -----

From: Andy Talbot

To: rsgb_lf_group@blacksheep.org

Sent: Tuesday, March 08, 2011 8:42 PM

Subject: LF: VLF Stability and soundcard locking

It would appear that a typical soundcard isn't stable enough for VLF use when stations are running 1mHz bandwidth signalling, and using any locking option to other off-air signals is a bit restrictive in what software you can run.

 

It may be worth looking at a custom codec driven from a locked frequency source.   The PCM2900 (which costs only a few pounds from Farnell, and they supply the data sheet) is a self contained USB codec which needs only a handful of additional components for a USB soundcard with stereo line input and output.     For normal operation it needs a 12MHz crystal, but an external 12MHz source can be used which could be locked to, or derived from, a high stability reference.  Even a TCXO on its own with typically 1ppm accuracy / stability would be better than any normal 20ppm crystal

 

I've built one of these codecs, but have yet to confirm the resulting sampling rate(s) are exactly what they should be.  By the time it has gone through USB packetising and Windows'  drivers I hope full synchronicity is maintained right through to the user software.   This may only be the case for sampling rates like 12000Hz - it all depends what windows does.   Exact conversion is needed for this solution to be worthwhile, not just a close approximation.

 

Andy

www.g4jnt.com