Re: LF: VLF Transmissions - G3XIZ - 12th / 13th February

[Chris Osborn <g3xiz@yahoo.co.uk>]

Mal,

I calculate the PA including the mains transformer is about 70% efficient.

The push-pull FET's are wired to the 10 - 0 - 10V windings and the output tappings are at 0 and 240 volts.
It has a laminated iron core.
The measured secondary voltage is about 350 volts rms so I dare not push the output power any higher.
I'm hoping that with a more efficient loading coil the secondary voltage will reduce and I can then push more power, hence current into the aerial.

I initially tried a LOPT but found the power output very limited.
Maybe I was doing something wrong !

73 Chris G3XIZ

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From: mal hamilton <g3kevmal@talktalk.net>
To: rsgb_lf_group@blacksheep.org
Sent: Fri, 11 February, 2011 16:15:43
Subject: Re: LF: VLF Transmissions - G3XIZ - 12th / 13th February

Chris

How efficient is ur mains transformer at 9 Khz, what sort of core, ferrite or laminated iron

I assume from what u say you couple your 5 ohm impedence PA to this transformer PRIM and output from the SEC to the antenna loading coil. Is the PRIM normal 250v and what is the sec voltage. or do u use a 6v winding. etc

I have a selection of mains transformers which I could ck out.

Have u tried instead a LOPT

de mal/g3kev

 

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

From: Chris Osborn

To: rsgb_lf_group@blacksheep.org

Sent: Thursday, February 10, 2011 7:23 PM

Subject: Re: LF: VLF Transmissions - G3XIZ - 12th / 13th February

Mal, Roger, Stefan and group

Thanks for the good wishes.
It will all depend on weather conditions as to whether I can fly the balloons but I shall keep you posted via the reflector.

I can try longer QRSS periods but begrudge the long wasted 'off' times especially if I'm having trouble keeping the balloons aloft.
A compromise would be for me to manually cut the carrier for 5-10 minute periods.

The transmitter feeds the loading coil and aerial via a large step up (mains) transformer.
The TX/ transformer will push its RF power into 2000 - 3000 ohms which is an approximation of the aerial circuit resistance when resonant..
I tried using a 50 ohms TX output and link coupling to the loading coil but without success.

The aerial current should be as before about 0.15 - 0.2 A

73
Chris G3XIZ

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From: Stefan Schäfer <schaefer@iup.uni-heidelberg.de>
To: rsgb_lf_group@blacksheep.org
Sent: Thu, 10 February, 2011 19:05:02
Subject: Re: LF: VLF Transmissions - G3XIZ - 12th / 13th February

Hi Chris,

I think DFCW-600 or even 2400 is a good compromise between a constant carrier and some ID but 60 is probably to fast. Jim received you in less than 2 mHz if i remember correctly. QRSS60 is to fast for that. Looking forward to your results :-)

73, Stefan

Am 10.02.2011 18:52, schrieb Roger Lapthorn:

Hi Chris,

Very good luck. I'll be looking for you and hoping for success this time.

An email direct and to this group saying when TX starts/ends would be helpful. Don't suppose you can send QRSS60 or similar to help with ID? Have passed the word on to Nick G4IKZ as he is closer to you than me and not sure he subscribes to this list.

73s
Roger G3XBM

On 10 February 2011 14:42, Chris Osborn <g3xiz@yahoo.co.uk> wrote:

LF,

 

I have had permission to transmit on VLF this coming weekend: 12th and 13th February.

Weather permitting I shall try again with my balloon-launched aerial, hopefully about 50m vertical.

 

The frequency will be

 

8.976 66 kHz  (i.e. 10.000 MHz / 1114) and is derived from an oven controlled xtal oscillator.

Hopefully the frequency will be more stable than last time.

If this frequency proves unsuitable I can transmit on 10.000 MHZ / 1112 . .10.000 MHz / 1116  etc.

 

I shall send a continuous carrier as and when conditions permit.

 

My newly built VLF TX is working well and can deliver about 150 watts of RF.

On this occasion I shall be using the original (fairly lossy) loading coil but am presently making a more efficient one.

 

All reports will be most welcome.

 

73

Chris G3XIZ

 

 

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