Message 20916 in TECH.WW
From: G8MNY
Date: Thu, 16 Apr 26 08:27:00 Z
Newsgroups: TECH.WW
Subject: BURNS's MF-UHF Wavemeter TC-101
Message-ID: <57377_GB7CIP>
Path: N2MH4|GB7BED|GB7YEW|GB7CIP
R:260416/0832Z 30290@N2MH4.#SENC.NC.USA.NOAM LinBPQ6.0.24
R:260416/0831Z 9880@GB7BED.#21.GBR.EU LinBPQ6.0.25
R:260416/0831Z 17234@GB7YEW.#79.GBR.EURO LinBPQ6.0.24
R:260416/0827Z @:GB7CIP.#32.GBR.EURO #:57377 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Correction Sep 12)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
Here is a reverse engineered diagram & layout of one I picked up the other day.
FRONT PANEL
LAYOUT
CIRCUIT
500-200 200-57 57-18 18-6 6-2.2 2.2-0.8MHz
HOW IT WORKS
The input from a 2 turn loop probe feeds low impedance test signals to the "TV
Belling Lee" input socket. The 6 pole 2 bank switch is actually a 4 bank band
change type with 2 earthing contacts banks on the unselected bands. The lower 4
bands the ferrite cored preset coils L3-L6 are quiet conventional with a 1 turn
drive primary, the layout not too important for the low frequencys.
_
The tuning capacitor is a constant frequency snail shaped type, /~ ~\
For the VHF range L2 is a thick wire loop split into two by the switch. Layout
is everything to getting the right L and stay capacitance for the indicated
frequency on this range.
On the same tuning cap there is a UHF 20pF section and a 2cm long copper strip
folded across it that forms L1. The coax drive tap is placed 25% from ground,
and the diode D1 detector on the 50% top of the U bend. Layout & small size at
UHF is needed for stable calibrated scale.
Note that in this circuit the germanium/Schottky diodes D1 & D2 are in series
on UHF range! But this does not affect the sensitivity much with the 50uA
meter. Input power (e.g. direct connection or PA pickup) should be limited to
below 100mW if the diodes are not to be dammaged, as there is quite a bit of
voltage step up!
Also look at my TECH buls on "Piston Absorption Wavemeter", "AKD's VHF/UHF
Wavemeter WA1", & "RF Field Indicator FL-30AH".
Why Don't U send an interesting bul?
73 de John G8MNY @ GB7CIP
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