|[AMRadio] Frequency Response|
jcandela at prodigy.net
Sat Sep 25 11:27:06 EDT 2004
I have always admired what Don has done with his modulation system. That 3400 hertz brick wall filter is a rarity unless one uses high technology active circuitry such as active op-amps, switched capacitor filters, dsp, etc. I believe Don has a passive module that does a great job. I wonder where he got it?
Also consider your individual voice characteristics, microphone, and speech polarity when building a modulation system.
Donald Chester <k4kyv at hotmail.com> wrote:
>What is a good ballpark response that I should use for operating AM in the
I would shoot for minimum of 100~ to 5000~.
According to the UTC catalogue (United Transformer Co.), to keep phase shift
distortion to a minimum, the response capability of the transmitter should
run one octave above and one octave below the actual response used, so a
transmitter with 50~ to 10,000~ capability would sound better even with
restricted response of the audio actually used.
Of course, that would require broadcast quality components. I would suggest
running response tests on the transformers in the rig, and then make sure
the coupling components in the rest of the audio chain allow at least the
response of the most restricted transformer. If you feel you need to
further restrict the response in any way, it should be done right at the
microphone preamp. If you limit your overall response to 300-3000~ you
might just as well run SSB.
I have been able to get satisfactory results with a very sharp, brickwall
lowpass audio filter that cuts off at 3400~, in combination with a rising
response boost in the mic preamp beginning at 800~ and peaking at about 9 dB
from 2000~ to the cutoff frequency of the filter, while the low frequency
response remains flat down to about 40~.
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