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[CQ-Contest] 87A question

Subject: [CQ-Contest] 87A question
From: k8cc@mediaone.net (k8cc)
Date: Mon Jan 22 22:28:32 2001
At 01:01 AM 1/22/01 -0500, Dick Green wrote:
 >I don't know how they do the RF sampling, but even if they had to wait an
 >entire cycle at 1.8MHz to determine the frequency, that would still be less
 >than a millisecond. My guess is that the detection takes place faster than
 >that (and certainly faster at higher frequencies.) So, my conclusion is that
 >no audible portion of the dit is lost.

I suspect the sampling time is a lot longer than this.  While I'm not
certain which microcontrollers are used in the 87A, due to the age of the
design I will bet that their clock oscillators run a lot slower than 10
MHz.  Therefore, the CPU cannot measure frequencies such as 10M or 15M
(particularly with enough resolution to discriminate between) without a
divider between the RF input signal and the CPU.  While I've not done the
required math, my educated guess is that the actual sampling time is more
like 50-100 mS once these factors are taken into account.

I also don't know if its a valid assumption that the PIN diode T/R
circuitry is capable of withstanding hot switching, particularly on the
output.  I suspect the design will begin tuning on the dit, but will not
switch into transmit until the RF input signal is absent.


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