I sincerely appreciate the trouble people take on this list to spread
knowledge to a dumbo G3 with thinking circumscribed by 807's . I am here
more for that than for knowing where to buy a TSxxx mark 2 or a supply of
cheap litz wire..
I must clarify a calumny however ....
Any suggestion of snoring on Saturday is due to a misinterpretation of my
grunts of agreement and approval at various things declared by the
lecturer.. After all.....to call out Hear ! Hear! [or is it Here Here ? -
I never know ] or "Yeah man " or "Alleluiyah Praise the Jim "- would not be
in keeping with the serious mien of shock and awe adopted at the declaration
of 'fully loaded Q may well be lower' on these occasions. ...so I just
grunted my approval. How easily can a man be misunderstood in todays
multi-cultural society ........[of Great Britain with shrine at Potters
Bar.] ? ?
Why doesnt the UK licence just specify field strength at a fixed distance ?
[ in the far field naturally ] - OK , I jest
Thank you,
Bryan
---- Original Message -----
From: "James Moritz" <[email protected]>
To: <[email protected]>
Sent: 09 October 2006 21:56
Subject: LF: Re: erp ierp - bluff
> Dear Bryan, LF Group,
>
> > If a man from Ofcom turns up here and says "demonstrate that you are not
> > exceeding the 1w ERP specified in your licence" how would I
theoretically
> > dispose the dipole to which ERP refers . Assuming the rx antenna is a
> dipole
> > it would make a big difference how I oriented the Tx dipole to compare
> with
> > the inverted L and plastic laundry basket former-loading coil.
> >
>
> The ERP definition compares the field strength produced by the real
antenna
> to that of a half-wave dipole in free space. It is assumed the field
> strength is measured in the direction the antennas produce their maximum
> radiation. So theoretically, you would dispose the reference dipole with
its
> feed point where the feeder is connected to your TX antenna. It would be
> convenient (although not neccessary) to position the antennas so that the
> maxima of the radiation patterns of the two antennas coincided, and the
> polarisation was the same. For this, the reference dipole would be
vertical.
> Since it is a dipole in free space, you would also have to remove the
Earth
> somehow, which would be awkward. The dipole would also have to be cooled
to
> absolute zero, in order to make it "ideally" resistance free.
>
> Luckily, the Ofcom man won't ask you to do this, because he just needs to
> know the field strength that the dipole would produce if it was there,
which
> can be calculated from a simple formula:- E = 7*sqrt(P)/d, where E is the
> electric field strength, P is the power fed into the dipole, and d is the
> distance from the dipole. This can be turned round to tell him what the
ERP
> is if he measures the field strength d metres from your antenna:-
> P(erp)=(Ed)^2 /50. It's up to him to sort out the polarisation, direction,
> etc. of his measuring system to suit the signal.
>
> > Is there some way of showing and measuring distant FS without putting an
> > antenna there?
>
> In principle at least, you could use a bolometer to determine the field
> strength (or the power density anyway), i.e. place some absorbing object
in
> the path of the radiation and measure how much its temperature rises.
> Actually doing this would be fraught with practical problems, however.
There
> might be other ways of doing it which I can't think of at the moment.
>
> Certainly the FS will be different if the tx dipole is
> > broadside on or end on .
> >
> Yes, but the convention is that ERP has to be measured in the direction of
> maximum radiation
>
> > [ ps enjoyed the talk on Saturday - apology if closing my eyes to
> > concentrate on loop bandwith gave impression of dropping off ;-) ]
> >
> Your impression really had me fooled - very impressive! Especially your
> impersonation of snoring :-)
>
> Cheers, Jim Moritz
> 73 de M0BMU
>
> (BTW, it is EIRP, not ierp)
>
>
>
>
> > G3GVB/ Bryan
> >
> >
> > bandwidth gave the impression of sleep in the front row ;-) ]
> > ----- Original Message -----
> > From: "james moritz" <[email protected]>
> > To: <[email protected]>
> > Sent: 09 October 2006 14:46
> > Subject: LF: Re: erp ierp VY1JA
> >
> >
> > Dear Bryan, LF Group,
> >
> > ERP is defined by the field strength at a point distant from the TX.
Field
> > strength is a measure of how much signal is present at a particular
point
> in
> > space. Of course, if you place a receiving antenna at that point, the
> signal
> > level at the antenna terminals will be reduced if its polarisation does
> not
> > correspond to that of the signal. But the field strength itself does not
> > depend on the receiving antenna, or indeed the presence of any antenna
at
> > all.
> >
> > In practice, to measure field strength, you usually have to use some
kind
> of
> > calibrated antenna to convert the radio wave into an electrical signal,
> with
> > a known relationship between field strength and antenna output signal
> level.
> > It is up to you to ensure that any effect of mismatched polarisation (or
> > directional pattern, mismatch or any other kind of gain or loss)is taken
> > into account.
> >
> > Cheers, Jim Moritz
> > 73 de M0BMU
> >
> > -----Original Message-----
> > From: [email protected]
> > [mailto:[email protected]] On Behalf Of captbrian
> > Sent: 08 October 2006 20:01
> > To: [email protected]
> > Subject: Re: LF: Re: erp ierp VY1JA
> >
> > Well I always thought there was a large loss depending on the extent to
> > which polarisation differed between emitter and recvr.?
> >
> >
> >
> >
> >
> >
> >
>
>
>
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