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GM7HUD > FT817 28.04.07 11:50l 62 Lines 2261 Bytes #999 (0) @ WW
BID : 2C4562GM7HUD
Read: GUEST DL1RX VE7HFY DG4IAK
Subj: Re: Max current from mic 5v pi
Path: DB0FHN<DB0FOR<DB0SIF<DB0IDN<DB0MW<DB0SWR<DK0WUE<DB0RES<ON0AR<GB7SYP<
GB7ESX
Sent: 070428/0855z 61782@GB7ESX.#31.GBR.EU $:2C4562GM7HUD [Witham, Esx]NNA V3.1
G0FTD wrote:-
>
>
>> ZL1ANM wrote:-
>>> Also, you're aware that modern rigs generate AM in a low level
[snip]
>
> Somehow I don't think BBC WS , VOA et al are all using 500KW modulators
> to get punch - do you ;-) ?
>
From the 1930's document "The London Twin-Wave Broadcasting Station
Brookmans Park, (c) The British Broadcasting Corporation, Savoy Hill,
London"
"The two transmitters are identical in construction, and operate on the
principle known as 'choke control at low power'. That is to say, the
high-frequency oscillations are first of all generated at low power, then
modulated, and afterwards magnified to the full power of the transmitter."
Which suggests that one of the UK's largest AM broadcast transmitters
(140kW in 1939) was not using high-level modulation.
> I agree with HUD.
I'm not actually disagreeing with anyone for a change! I'll believe that
high-level sounds different to low-level but I want to know why. 100%AM is
100%AM so any difference between low and high level modulation has to be
something do with distortion products as my namesake mentions below:
> The "punch" came from all that harmonic distortion and emphasised freq
> response from mismatched mic inserts in reality.
>
>
> These days broadcasters (cue M0PZT) use Optimod units to introduce
> *selected*
> harmonic distortions to create a modulation "reinforcement" effect.
Ah The Optimod. It would appear to me that Optimods are used by local FM
commercial stations to achieve that immortal line from the opening dialogue
of Deep Purple's "The Mule" on their seminal 1973 album "Made in Japan"
which has Ian Gillan saying
"....we want everything louder than everything else...."
I'm old enough to remember when FM broadcast radio in this country implied
quality. Then along came commercial broadcasting and competition for
listeners.
DAB... we wont go there please. A fanatastic idea (almost CD quality)
broadcast music taken over by the idea that people want more choice and
less quality. Hence a bazillion stations transmitting mono 96kbps streams.
I'd rather listen to medium wave after dark!
I have to say that I've never seen the attraction to AM on amateur
frequencies. It just seems so wasteful of bandwidth and power.
73 de Andy GM7HUD
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