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G8MNY > TECH 17.02.25 16:41l 43 Lines 1773 Bytes #4 (0) @ WW
BID : 26192_GB7CIP
Read: GUEST
Subj: 23cm Filter
Path: JH4XSY<IW0QNL<SR1BSZ<EA2RCF<LU9DCE<LU4ECL<ED1ZAC<GB7CIP
Sent: 250217/0738Z @:GB7CIP.#32.GBR.EURO #:26192 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Dec 03)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
Here is a simple filter that will remove most unwanted signals often found as
unwanted images in 23cms Rx. eg UHF TV signals x2. It will also give some
static protection for preamps as the double tuned line is grounded, but the
loss can be as high as 2dB depending on materials! Bandwidth is quite narrow &
the filter will need tuning top to bottom of 23cm band. It is not suitable for
Tx over 1-2W due to the trimmer losses.
The I/P & O/P can be coax leads soldered straight to the box & line or BNC/F
connectors etc.
<-1.5cm-> <-1.5cm->
Coax or BNC Coax or BNC
^ ======= ! ======================== ! ========
1.5cm ｳｳ_________________________________________ｳｳ
v ｳｳ [^] Brass strip ｳｳ\...End Wall
====================! !======================
0.5-3pF \..Side Wall
< - - - - - - - - 8cm - - - - - - - - - - - >
It is made from double sided PCB 2cm tall all seam soldered up with the bottom
& end pieces slightly larger to allow inside & outside soldering of the side
walls. Leave the lid off until after the initial tune up.
The brass strip is 4mm wide (can be thick copper wire) & is soldered to both
end walls. The trimmer is a bolt in type, but soldered in ceramic ones from old
mechanical TV tuners will do.
Once it is tuning well, tack solder the lid on & retune, you should have
slightly better Q, make sure the tuning is OK before properly soldering up the
seam.
Why Don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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