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LF: Re: 500KHz NOV

To: <[email protected]>
Subject: LF: Re: 500KHz NOV
From: "Gary - G4WGT" <[email protected]>
Date: Sat, 28 Apr 2007 10:43:53 +0100
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References: <[email protected]>
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Hi Peter & LF,

I had a similar e-mail from Ofcom.

Copy of Ofcom mail & my reply below, the NOV was issued soon after.

I hope this helps.


Gary - G4WGT - IO83qp

Mr Taylor,
Thank you for your recent application for a Special Research Permit to operate in the bands 501 -504kHz. Your application is currently being processed pending authorisation.
Whilst this is in motion I would just like to gain further clarity on the
matter relating to ERP levels.
Could you therefore please provide a statement on how you propose to control
your transmissions to within the limit of <-10dBW
I appreciate that this was not an explicit requirement in the original
application however we do still need this information.
I await your response and, in the meantime, would like to take this
opportunity to thank you again for contacting Ofcom.
***********MY REPLY**************

Hello Mr Gohil,

Thank you for your e-mail.

I propose to control the transmissions from my 500 KHz station using the
following method, the PA stage of the transmitter will have two means of

1 - Variable DC voltage supply of 9 to 15 volts
2 - Tapped output transformer

I will adjust these variables whilst monitoring the antenna current to
maintain an ERP of no greater than -10 dbW.

My detailed explanation :-

The transmitter I propose to construct for this frequency will have a single
low power mosfet PA operating in class C or D mode with a variable DC
voltage supply of 9 to 15 volts to the output transistor and I estimate it
to produce 25 watts DC input.

Assuming around 90% efficiency this will give an RF output of around 22.5
watts to my 12 metre vertical Marconi top loaded antenna in my small garden
which I have calculated to be 1.07 % efficient at 504 KHz and will require
0.41 Amp aerial current for an ERP of -10dbW.

Taking into consideration the antenna efficiency, feeder and other losses I
doubt that this transmitter power will even allow the antenna to radiate -10
dbW ERP, I have calculated that 50 watts DC input will be required to meet
the maximum ERP allowed with my system. I have taken the steps to keep the
maximum available transmitter power low so as to easily maintain lower
than -10 dbW ERP.

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