Re: VLF: Transmit hardware

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

Hi Markus

 

Great development work always the unexpected in the best planning.

 

In UK 405 line TV was notorious for the 10kc/s whistle from the LOPTI (405x25 [interlaced] frame TB = 10125Hz) and even the modern 625 lineTV is / was noticable at around 15kc/s (kHz) by the younger generation with good ears... ;-)   

 

So, yes I can understand the issue now you bring it up.

 

BTW I have been looking with Sound card RX and LW but seem to be getting odd effects new to me BC AM break thro - also not seeing any Alpha stations? The big Mil stations are visible with a station on 18kc/s transmitting 12wpm CW at times then TTY and other phase shift transmissions..... the CW always ends with a K as though inviting a reply.

 

Thanks for your efforts Markus.

73 es GL petefmt

I support www.NotSpotTelecom.Com your community Telco / ISP.

--- On Sun, 10/10/10, Markus Vester <markusvester@aol.com> wrote:

From: Markus Vester <markusvester@aol.com>
Subject: Re: VLF: Transmit hardware
To: rsgb_lf_group@blacksheep.org
Date: Sunday, 10 October, 2010, 11:20

I got a complaint from the neighbourhood about acoustic radiation from the coil! So I interrupted the carrier for a few minutes around 12:35 and improvised a foam package for noise mitigation.

 

BTW It is quite remarkable that an air coil vibrates at 9 kHz and not 18 kHz, as Lorentz forces between windings should be a purely quadratic effect. I presume that the vibration is induced by the earth field - at only 50 uT it's amazing how strong the effect still is! The loudest part of the setup is the ferrite transformer, probably due to magnetostriction, with bias from some remanent core magnetisation.

 

Best wishes for a quiet Sunday,

 

MArkus (DF6NM)

 

 

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

From: M0FMT

To: rsgb_lf_group@blacksheep.org

Sent: Sunday, October 10, 2010 12:02 AM

Subject: Re: VLF: Transmit hardware

...

XYL has warned no coils on the roof here!............. hee.