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PA2RHB > TECH 28.02.03 00:15l 43 Lines 1553 Bytes #999 (0) @ WW
BID : 470211PA2RHB
Read: DB0FHN GUEST OE7FMI
Subj: "Explorers", how do they work?
Path: DB0FHN<DB0ZWI<DB0HDF<DB0ERF<DB0FBB<DB0GOS<DB0PKE<PI8DAZ<PI8WFL
Sent: 030227/2207Z @:PI8WFL.#NH1.NLD.EU #:7512 [Enkhuizen] $:470211PA2RHB
From: PA2RHB@PI8WFL.#NH1.NLD.EU
To : TECH@WW
Hi all, thanks for reading this.
There are at least some commercial makers of hand held "near-field"
receivers that will lock onto a transmission in a matter of a second or
far, far less, wherever in a range of, say, 30 to 2000 MHz the
transmission may take place.
So, it must "scan" the band very quickly, "lock in" to a transmission, and
demodulate it. All advertise FM demodulation, some will do AM as well, and
one really expensive one does all sort of tricks with DTMF, CTCSS and so
on.
Locking so quickly does mean they can't tell you the frequency to the
nearest kHz, but 100 kHz resolution seems normal.
I understand that such a device will lock on the first signal it meets
that is loud enough. There is a "skip" button, though. I could not very
well be very sensitive, for then it would stop _everywhere_. A gain
control seems usefull.
Question is, "How do they do it"? Synthesizing all those channels so
quickly could be very expensive, then again, some _are_. But perhaps an
analog system could work, sweeping a VCO from 2 to 4 GHz, with 2GHz as the
first IF (immediately followed by a mixer to something more manageable).
Super sensitivity would not be needed.
Has anyone tried to make something like this?
Has anyone some tips as to what may be in the commercial ones, especially
the cheaper ones? (FC-5001 springs to mind).
Or perhaps you see this idea for the first time and Presto, you think of
an answer..
Thanks again, and cheerio,
Rudolf, PA2RHB
Heemskerk, The Netherlands.
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