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From: Talbot Andrew <ACTALBOT@mail.dstl.gov.uk>
To: rsgb_lf_group@blacksheep.org
Date: Tue, 10 Oct 2006 12:08:00 +0100
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Subject: LF: RE: Re: RE: Re: Re: erp eirp - bluff
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Welll........
As as an isotrope is a point source, it must have one dimensional
polarisation mustn't it :-}

In reality, polarisation cannot be defined - a true omnidirectional radiator
is (probably) not possible.  If it were, its polarisation would have to be
uniform in all directions at the same time.

Having said that, I remember being told by someone who worked on the UK
space programme in the 1950's that they put up an ionospheric drag
monitoring satellite that consisted of a completely spherical spacecraft
that they wanted to freely tumble. The diameter would have been in the
region of 0.5 to 1 metre I imagine.  Consequently it had to have a good
isotropic radiating pattern at VHF.  They ended up with a surface made up of
three equal sections each fed 120 degrees out of phase that exhibited a
pattern within 1.5dB of isotropic.   With a radiatiator made up of three 1m
type sections, there must have been some polarisation sensitivity, and that
probably comes into the 1.5dB error budget.

Working in a government scientific establishment in those days must have
been quite interresting.

Andy  G4JNT


-----Original Message-----
From: owner-rsgb_lf_group@blacksheep.org
[mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of captbrian
Sent: 10 October 2006 11:06
To: rsgb_lf_group@blacksheep.org
Subject: LF: Re: RE: Re: Re: erp eirp - bluff

Aha I wasn't so stupid then.....
Now ,  you asked for this.......what is the polarity of an   'isotropic '
radiator .?

Bryan
----- Original Message -----
From: "Talbot Andrew" <ACTALBOT@mail.dstl.gov.uk>
To: <rsgb_lf_group@blacksheep.org>
Sent: 10 October 2006 08:04
Subject: LF: RE: Re: Re: erp eirp - bluff


> It should be, but the 'rule makers' way-back-when in their infinite 
> wisdom decided that dipoles were easier for the humdrum public to 
> visualise so defined ERP as being relative to a perfect dipole.
>
> As it is difficult to make dipoles at high frequencies (actually it is 
> a
lot
> wasier easier, but... Never mind) ERP there was defined as being 
> relative
to
> isotropic.  So...
>
> Below 1000MHz ERP is defined as being realitive to a dipole, above 
> 1GHz
ERP
> is defines as being the same as EIRP.
>
> Its just a matter of semantics.  I fell into this trap and queried the 
> ERP limits when 50MHz was first introduced several decades ago.  50MHz
requires
> EDRP, so the actual maximum RF power could be more than would be 
> needed
for
> an isotrope.
>
> Andy  G4JNT/G8IMR (still lurking)
>
>
>
> -----Original Message-----
> From: owner-rsgb_lf_group@blacksheep.org
> [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of captbrian
> Sent: 10 October 2006 03:13
> To: rsgb_lf_group@blacksheep.org
> Subject: LF: Re: Re: erp eirp - bluff
>
> Then why isn't ERP called  EDRP ?
>
> eg  EIRP, EMRP, EDRP ......s'obvious innit.?
>
>
> ----- Original Message -----
> From: "James Moritz" <james.moritz@btopenworld.com>
> To: <rsgb_lf_group@blacksheep.org>
> Sent: 09 October 2006 21:56
> Subject: LF: Re: erp ierp - bluff
>
>
> > Dear Bryan, LF Group,
> >
> > >< snip >>
>
> > Cheers, Jim Moritz
> > 73 de M0BMU
> >
> > (BTW, it is EIRP, not ierp)
> >
> >
> >
> >
> > > G3GVB/ Bryan
> > >
>
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