[Lf] Experimental LF transmitter]

[Andre' Kesteloot]

Richard Rogers wrote:

> G'day All,
>
> I now have my PIC running at 10.245MHz, generating 182.9KHz, with 43% duty
> cycle.
>
> I measured the TX output as 196 watts at 104% efficiency with 5 volts on
> the driver and 205W and 114% with 12V!
>
> These odd figures turned out to be because my dummy load was not 50ohms,
> but 58ohms.   The corrected figures are 169W at 90% and 176W at 96%.   I
> suspect these are probably not accurate also, but at least the trend is
> clear.   There is now a slight improvement with the higher drive voltage.
>
> The loss formulae in the Hitachi book are a bit hard to explain without
> their diagram so I'll simplify it a bit by neglecting the switch on loss.
>
> I assume they mean f to be frequency.   t2 = on time and Ip is the peak of
> the triangular drain current, then P2  = (f x t2 x Rds x Ip^2)/3.
>
> For the switch off loss, t3 is the switching time and Vp is the peak drain
> voltage, then P3 = (f x t3 (Vp x Ip + 2 x Ip^2 x Rds))/6
>
> I'll check these with f=180K, t2=5.4uS, Rds=.1, Ip=20, t3=200nS, Vp=80
> Then P2 = 13W and P3 = 10W
>
> Many thanks for your help.
>
> 73, Ric, VK7RO