swood@vela.acs.oakland.edu ( EVENSONG) (09/24/90)
I just got one of those "deals you can't pass up" at the local flea market on a grid dip meter by Eico. The catch: no coils. I got the thing for $2 though. I was wondering if anyone might know where I might get some coils, or how I may go about making some perhaps? swood
larry@kitty.UUCP (Larry Lippman) (09/24/90)
In article <3110@vela.acs.oakland.edu>, swood@vela.acs.oakland.edu ( EVENSONG) writes: > I just got one of those "deals you can't pass up" at the local flea market > on a grid dip meter by Eico. The catch: no coils. I got the thing for > $2 though. I guess we all basically get what we pay for. :-) > I was wondering if anyone might know where I might get some coils, or how I > may go about making some perhaps? I have an EICO Model 710 Grid Dip meter, which is probably what you have. I have no manual for it, however. I will tell you what I know about the coils, and perhaps other readers can add to it. The EICO model 710 uses eight coils labeled "A" to "H" to cover the frequency range of 0.4 to 250 MHz. The lower frequency coils have a tapped winding, while the upper frequency coils do not. The following chart tells you all I know: COIL FREQUENCY TAP DESCRIPTION OF COIL "A" 0.4 - 0.7 MHz yes lots of turns of Litz wire & tuned slug "B" 0.7 - 1.38 MHz yes lots of turns of Litz wire & tuned slug "C" 1.38 - 2.9 MHz yes lots of turns of Litz wire & tuned slug "D" 2.9 - 7.5 MHz no approximately 30 turns of 28 AWG enamel "E" 7.5 - 18 MHz no approximately 15 turns of 24 AWG enamel "F" 18 - 42 MHz no approximately 6 turns of 20 AWG enamel "G" 42 - 100 MHz no approximately 2 turns of 18 AWG enamel "H" 100 - 25 MHz no 1/2 turn U-shaped 0.125" wire loop The coil forms for "A" to "G" are all 0.75" plexiglass, with the coil winding being about 2" from the pins. Armed with the above information and some trial and error, you could probably duplicate the required coils. Larry Lippman @ Recognition Research Corp. "Have you hugged your cat today?" VOICE: 716/688-1231 {boulder, rutgers, watmath}!ub!kitty!larry FAX: 716/741-9635 {utzoo, uunet}!/ \aerion!larry
swood@vela.acs.oakland.edu ( EVENSONG) (09/24/90)
Hey! The 710 is the very animal that I have. (Eico 710, 8 bands from .4-250 MC) Any one have any hints on how to create and tweak coils for this animal? Pretend I don't know anything about building resonant coils for dip meters, and you won't be far from off. (I have had a lot of work with resonant loads, from antennas to resistance networks, but have never worked with dip meters - perhaps I would have been more successful if I had) Thanks. swood
larry@kitty.UUCP (Larry Lippman) (09/25/90)
In article <3113@vela.acs.oakland.edu>, swood@vela.acs.oakland.edu ( EVENSONG) writes: > Hey! The 710 is the very animal that I have. (Eico 710, 8 bands from > .4-250 MC) > > Any one have any hints on how to create and tweak coils for this animal? > Pretend I don't know anything about building resonant coils for dip meters, > and you won't be far from off. Get some 0.75" OD plexiglass tubing and cut it in 2.5 inch lengths. You'll have to use some ingenuity in fabricating pins to fit the socket on the end of the grid dip meter. Heavy solid wire, like some tinned 12 AWG may be about right. The grid dip meter is tuned *solely* by the inductance of the coil; there is obviously no bandswitch on the instrument. While the 3 lower frequency coils may be tricky since they are tapped and I cannot estimate the turns, the higher frequency coils from 2.9 MHz to 250 MHz should be easy to build. Just start with winding a coil based upon the description in my previous article. All you need to test is a sensitive frequency counter. Set the scale on the grid dip meter to a given frequency. Take the test leads from the counter and loosely wrap a turn around the coil form for inductive coupling. Merely add or remove turns on the coil until the grid dip meter calibration matches the reading on the frequency counter. These coils, by the way, are not exactly hi-Q, so I wouldn't sweat your fabrication technique. I can't do much more than tell you the above. Larry Lippman @ Recognition Research Corp. "Have you hugged your cat today?" VOICE: 716/688-1231 {boulder, rutgers, watmath}!ub!kitty!larry FAX: 716/741-9635 {utzoo, uunet}!/ \aerion!larry
whit@milton.u.washington.edu (John Whitmore) (09/25/90)
In article <4052@kitty.UUCP> larry@kitty.UUCP (Larry Lippman) writes: >In article <3113@vela.acs.oakland.edu>, swood@vela.acs.oakland.edu ( EVENSONG) writes: >> Hey! The 710 is the very animal that I have. (Eico 710 > > Get some 0.75" OD plexiglass tubing and cut it in 2.5 inch lengths. > > The grid dip meter is tuned *solely* by the inductance of the >coil; there is obviously no bandswitch on the instrument. While the >3 lower frequency coils may be tricky since they are tapped and I cannot >estimate the turns, the higher frequency coils from 2.9 MHz to 250 MHz >should be easy to build. > ... [more helpful information, followed by] > > I can't do much more than tell you the above. But if you've got a working grid dip meter, you can tell him the inductance of the taps on the coils; just clip a capacitor onto the taps and measure away with ... a grid dip meter. Since the things are low frequency coils with the inbuilt tuning capacitor (circa 50 pF), this will likely require using either another grid dip meter, or measuring only the higher-frequency tapped coils ('cuz you're unlikely to be able to estimate the stray capacitance better than a large fraction of that 50 pF.) The inductance, of course, goes as the square of the turns ratio. John Whitmore