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.
73
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
control,
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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