"One of the complaints that
we were aware of was that some commercial pre-amps suffered from
being driven into distortion from broadcast and other sources nearby
in frequency."
BCNU DE N2LO
I'm surprised that none's mentioned the PRE-1 & 2 preamps that K9AY
builds. I tested the PRE-2 in my company's lab and found it has an
excellent IP3 and very good rejection of BC signals. I don't have the
numbers in front of me, but I believe they were 50 dB or better.
There's another parameter that hasn't been mentioned in this thread.
I've wondered about the effects of impulse-response in preamps. When
a preamp increases the width of narrow (short-duration) pulses such as
those we hear from lightning discharges, the receiver may be
effectively disabled for the duration of the pulse. I injected 20
nS-wide, positive-going pulses and looked at the preamp output on a
fast, digital scope. Some preamps reproduced them perfectly. Others
rang like bells for as long as several milliseconds.
The PRE-2 did very well in these tests, even though it has tuned
circuits ahead of the active device. The rule is, the more
selectivity you put ahead of the preamp, the more likely the tuned
circuit will store the energy in a pulse and release it slowly. The
PRE-2, which covers 160 through 40 meters and rejects the BC band is a
good compromise in this respect.
I can email data if anyone is interested in seeing it.
73,
Brad, KV5V
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