General Practice My Dipper
VARIOUS SCHEMATIC, HOW TO USE AND ACCESSORIES
HOW TO USE DIPPER
ACCESSORIES FOR DIPPER
(Click on a picture to see it bigger)
WITH BIPOLAR TRANSISTOR
WITH TUNNEL DIODE
HOW TO USE DIPPER
Put the dipper and the circuit to test together; usually I start putting the dipper coil very closed and parallel to the circuit; keep away from circuit any metallic objects; switch on your dipper and turn slowly the VFO knob until you can see a big dip in the meter; if ther's no dip, try again with an other coil. Now move the dipper away from circuit as far as the dip is very low (probably it will be necessary to retuning vfo fine): measure now the frequency using a frequency meter or, better, a monitor receiver.
It's the same as above (see Picture):
Put a well known capacitor in parallel to a coil; measure the resonance of LC circuit with dipper (the meter will show a big "dip": it's the resonance point);
Place the dipper as far as possible from the LC circuit (until the dip on the meter is very low): ok, take note of the frequency; with the below formula you can now know the inductance of the coil:
MicroHenry = 25330 : (MHZ x MHZ x pF).
It's not a very fine measure of Q but...we are hams; make the same as above;
as far you can read the dip, as high is the Q of coil (you need to use a good-high Q capacitor).
It's similar to Inductance measure but now you know L value: use the following formula:
pF = 25330 : ( MHZ x MHZ x MicroHenry).
MEASURE OF COAXIAL CABLE LENGTH
AND FACTOR OF VELOCITY:
to measure coaxial cable (i.e. 1/4 or 1/2 wave for building stub, filters ecc.) cut the cable something more than half wave;
NOTE: with the dipper you can measure the electrical length and not phisical one (the phisical length is the one you measure with a meter); you can obtain the electrical length dividing phisical one by velocity factor; for hard-dielettric cable, as RG213, RG8, RG58, it's 0,66, for other it's about 0,89 (foam TV cable);
so if you need a 1/4 wave cable for 28.500 you need at first the one wave length (Lambda);
Lambda=300/F >>>>> 300/28.500=10,52 meter;
1/4 wave= Lambda/4 >>>>>> 10,52/4=2,63 meter;
this is the 1/4 wave length is velocity factor of the cable is 1, but suppose you're using RG213 (F=0,66); so
2,63 x 0,66=1,73 meter;
cut the cable at about 1,8 meter; shortcut both ends (one with a small loop where put the dipper); switch on your dipper at about 28.000 MHz and put it near the small loop on the cable; you should have dip lower (infact we have cut the cable longer); after found the dip, cut the cable step by step, until you find the dip at 28.500 (remember to short-cut one end of the cable);
now we have 1/2 wave, just half-cut it and you'll have your 1/4 wave coaxial stub;
NOTE: measure the cable length from the points where the screen is over the central wire; make sure to not shorten it when soldering PL259 (the PL length is part of the lenght).
Sometime it's better to open one end of the cable and measure directly a 1/4 wave (i.e. your dipper can't go up 100 MHz and you need 1/2 wave on 200 MHz; measure a 1/4 wave at 100 MHz and it will correspond to 1/2 wave at 200 MHz).
You can also measure the velocity factor of an unknown cable: measure at first phisical length and than the resonance frequency (of course, if you have a 2 meter cable, you should expect resonance at about 25-30 MHz, be careful with arnmonic resonance);
as usual (see picture).
ACCESSORIES FOR DIPPER
SEPARATOR: it's useful to pick up RF signal generated by dipper for reading it on an external frequency-meter or to use dipper as signal generator; it's a simple high-impedance RF amplifier (See Picture 1).
MODULATOR: it's an audio frequency generator that modulates the RF signal with a tone: useful to make the RF signal more "visible" (See picture 2).
XTAL TESTER: as the same word says, it's a circuit to test the xtal efficiency (See Picture 3);
LC BRIDGE: it's a simple variable capacitor with a graduate scale and a coil; knowing C and F value you can know L value (or knowing L and F > C, see use of dipper for capacitance and inducatance measure) (See Picture 4).