On Oct 11, 2004, at 1:40 AM, peter.chadwick@Zarlink.Com wrote:
One point to bear in mind is that the secondary of the modulation
transformer has a lot of DC in it, which means that you need more iron
(and probably an air gap) to avoid the core being saturated by the Dc
feed
to the PA. This is apparently why modulation reactors are used - the
transformer is designed for no DC, and feeds through a blocking
capacitor
to the plate supply and ground, there being the 'modulation reactor' in
series with the plate supply to avoid the AF being shunted. The
etchniques
is apparently fairly common in the AM broadcast area for powers of 1
to 5
kW.
- This was common practice in ancient times, and it substantially
improved the bass response of the modulation transformer, however, I
doubt that very many "plate modulated" AM broadcast transmitters are
presently being produced. The excellent sounding AM signals that I
have heard on the Ham bands use a low-level modulator IC and linear
amplification.
cheers, Peter
Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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