[cma-l] AM v FM

[Ian Hickling]

I do sincerely agree
But with the amount of land required, plus the structure and its erection, plus the earth mat and ATU - the construction of an aerial which is anything like naturally resonant is a major project and expense.
Hence they are nowhere near a quarter wavelength and need added capacitance and inductance in order to achieve a reasonable match.
This also introduces a huge question mark over the shape of the propagation envelope and removes any hope of effective modelling.
So overall efficiency is about 8 to 10%

Ian Hickling
Partner

Office: 01635 578435  (7am-11pm UK time)Carphone: 07530 980115 (only responds when driving)6 Horn Street, Compton, NEWBURY, RG20 6QS

> From: tlr at gairloch.co.uk
> To: cma-l at mailman.commedia.org.uk
> Date: Mon, 14 Dec 2015 17:11:10 +0000
> Subject: Re: [cma-l] AM V's FM
> 
> >
> > If you need to generate 800W of RF for an EMRP of 70W I'd say you need to
> > improve your antenna system efficiency :-)
> >
> 
> As you know, easier said than done for a small station David! With a typical 
> wavelength of 200-300 metres, an efficient omnidirectional radiator can be a 
> mighty big thing. A traditional quarter-wave vertical mast is not something 
> you can just pop on a roof pole like an FM dipole! Loading coils can shorten 
> it, but nonetheless efficiency rapidly falls off as you make the antenna 
> more compact.
> 
> A more surprising figure is Ian's implied 28% electrical efficiency for the 
> AM transmitter - Nautel's J1000 offers 60%-70% efficiency (ie ~1300W 
> consumption for 800W modulated output). The Nautel TX costs around £10k, but 
> it would save around £1,800 electricity a year in Ian's example, so would 
> probably pay back the extra cost in a little over 2 years.
> 
> Alex
> 
> ----- Original Message ----- 
> From: "Info" <info at transmittersrus.com>
> To: <cma-l at commedia.org.uk>
> Sent: Monday, December 14, 2015 4:03 PM
> Subject: [cma-l] AM V's FM
> 
> 
> > Ian,
> >
> > If you need to generate 800W of RF for an EMRP of 70W I'd say you need to
> > improve your antenna system efficiency :-)
> >
> > David
> > Transmitters 'R' Us
> >
> > _______________ 
> 
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