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G8MNY > TECH 10.09.04 19:38l 149 Lines 6654 Bytes #999 (0) @ WW
BID : 10122_GB7CIP
Read: DL7NDF GUEST OE7FMI
Subj: Piston Absorption Wavemeter
Path: DB0FHN<DB0THA<DB0ERF<DB0FBB<DB0GOS<ON0AR<ON0AR<7M3TJZ<IK1ZNW<GB7CRV<
GB7CIP
Sent: 040910/1540Z @:GB7CIP.#32.GBR.EU #:10122 [Caterham] $:10122_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (New Feb 04)
This ¬ wave line meter can detect Tx frequencies from 70MHz to 1.3GHz in one
range. With an accuracy of about 1%. At the higher frequencies 3/4 or 5/4 wave-
length resonance modes also give good accuracy.
PRINCIPLE
RF is coupled into a variable length ¬ wave resonator. At resonance a pickup
loop drives a diode detector to give an indication to a meter. As the length is
varied the exact position of the peak is indicated on a frequency (wavelength)
scale.
HARDWARE
1.1M of 25mm Square Aluminium tube.
1.1m of 3 to 5mm Brass rod.
x1 22x22x6mm or thicker Aluminium Blanks (off old heatsink?)
2x Chassis sockets N or SO239 or BNCs
4 Screws eg Steel 4BA CS.
8 pop rivets/Self tap screws
2cm of plastic support rod (heat glue stick)
Steel Wire (Coat hanger)
Clip to support Steel wire!
1x Signal diode
10cm of 18-25swg enamelled copper wire
1x 1n feed through cap (bolt type).
TOOLS
Metal Saws
Metal Files
Taps for screws
Pop Rivet Gun (with tube collar!)
Drill & bits for Screw tap & clearance.
Blow lamp / large heat source.
70cm & 2M Tx for calibration.
CONSTRUCTION
1/ An Aluminium blank need to be made to closely fit inside the end of the
tubing, at least 6mm thick plug.
2/ Fit the blank, drilled 4 tapping holes one each side of the tube. Mark the
blanks position & remove.
3/ Tap the blank to take the screws. Drill clearance holes in the tube.
4/ The blank is centrally drilled out/filed to be a tight sliding fit to the
brass rod.
5/ Drill holes for the RF sockets (pop rivet size/self tap) in the tube near to
the blank as possible, with then as close to each other as possible.
6/ Solder a thick wire to make the Driving link on one of the sockets.
Check that it clears the Brass rod OK. Pop rivet/screw in place in the LOAD
position.
7/ Put the Tx Socket in place Pop rivet that & solder up the link.
8/ Drill a hole for the bolt in feed through capacitor in the tube opposite to
the load socket.
9/ Solder the signal diode with minimum lead to the capacitor. Then solder a
wire to free end of the diode to make the detection loop.
10/Fit the capacitor making sure that all the bits will clear the brass rod.
11/File or saw a slot in the blank to ground the detector wire. Bare the end of
the wire. The wire can be placed under a blank fixing screw if needed.
12/Place the blank & brass rod in place. Push the brass rod so it just
protrudes from the tube open end. Cut the spacer plastic bar to neatly fit
diagonally across the tube. Drill an undersized hole centrally on it. Heat
the brass rod up & force into spacer. This should attach it OK. Otherwise
glue it.
13/Bend up a coat hanger wire to make the frequency pointer. A few turns
around the brass rod & soldered up will attach it.
14/Put a small cable clip (folded P shaped type) as a guide around the sliding
wire & use a blank fixing screw & washer to hold firmly in place.
15/Attach a sensitive meter (& a pot) to the detector O/P & connect some RF.
If moving the rod you can see a peak, then you can do the calibration.
Tx Load
Screws ÚÄ0Ä¿ ÚÄ0Ä¿
\__³ ³ ³___³ ³ ³_______________________________________________________
Blank³ ³ ÀÄÄÄÄÄÄÄÙ Tube | | ³
³ ³ Driving link Spacer| | ³
O======================================================================== ³
³ ³ ³ ÚÄÄÄÄÄÄÄÄÄ¿Pick up Brass Rod | | ³
³ ³_³/__________D____________________________________________________|_|_³
³ CLIP ³Feed C FREQUENCY SCALE
ÀÄÄ(--------------------------------------------------------------Ä----ÄÙ
Coat Hanger Wire
SCALE ==o
ÚÄÄÄÄÄÄÄ//ÄÄÄ¿
RF ³ // ³
SocketsÚÄÄÄ´ // ³ C
³ ³= 0 ³]---------¿
ÀÄÄÄ´ Brass ³ POT<--METER
POP Rivets>³ Rod ³----------Á---Ù
ÀÄÄÄÄÄÄÄÄÄÄÄÄÙ
\ Blank
x4 Screw
Fixings
CALIBRATION
Two frequencies are needed for this as the electrical end point, will not be
the same as the brass rod physical end (usually outside the tube!). Using 2M &
70cms markers it should be quiet easy to extrapolate the full scale.
Reference
Infinity 432MHz 144MHz
???? ³ ³
point
The distance between 432 & 144MHz marks is exactly 2x the distance from the
Reference scale infinity to 432. Note 432MHz will also produce resonance around
the 144MHz mark as a 3/4 wave resonance. Ignore the longer resonances for now.
End point (144-432 marks mm)
from 432 D432 = ----------------- mm
Mark 2
So place a length light coloured tape under the coat hanger pointer & mark off
all the known frequency lines you can. Accurately measure these & put into a
chart (eg a spread sheet) to calculate the length of any frequency.
Distance from D432 * 432
End point for DFx = ---------- mm
Fx MHz Fx
Now make a scale chart for 70,75,80,85 90,95,100,110,120,130,140,150,160,170,
200,250,300 400 500 600 700 800 900 1000MHz
1.1, 1.2, 1.3 GHz. Note the high frequencies a very close together & suitable
marking are difficult.
= = = ==
³ ||³||³||³ ³||||³ ³||||³||| ³ | ³ | ³ ³||||³ ³|||| ³ ³ ³||||³||||³ ³
ì 1 7 5 4 3 2 2 1 1 1 1 1 1 9 8 8 7 7
G 0 0 0 0 5 0 7 5 3 2 1 0 0 5 0 5 0
H 0 0 0 0 0 0 0 0 0 0 0 0
Then engrave these measurements onto the tube leaving room for a 3/4 & 5/4
wave scale sets if you want to add those in further calibration scales.
IN USE
I high lighted the ham bands in coloured felt pen. You should find that they
show up as quite wide bands, as 2MHz of 2M is 1cm long. So if you have been
accurate in the scale marking, basic frequency measurement down to about 1%
should be possible.
Powers of 100mW - 50W should be OK mainly limited by the diode PIV.
Although this is not a spectrum analyser etc, it is able of detecting high
levels of harmonics & strong side spurii.
Why Don't U send an interesting bul?
/QSL
73 de John G8MNY @ GB7CIP
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