gimmick

Cute idea! I traditionally use only #24 Teflon wire on any of my breadboards ...Jim Thompson

What I mean is, being long married, one isn't going to be doing anything about it either way, so why worry? ;)

Cheers

Phil Hobbs

I wrote that after midnight. No warranty expressed or implied.

It does badly in vibration because it has to be elevated above the PCB to reduce capacitance to the PCB ground, and to allow for adjustment range. We used it for high-Z filter coupling capacitors where it was physically impossible to install a cylindrical trimmer. I sized the above numbers for the specified capacitance range. If 2.8 mm minimum overlap is too little for stable operation, high voltage wire, with more insulation should allow for longer wires.

We actually did run a vibration test on the radio and found that the cantilevered capacitors broke where the wires entered the PCB. More hot melt glue was the quick fix. Adding a Bivar component mount was better (because it made production happy). The capacitor still flopped around but due to the low mass and short lever arm, never hit any real mechanical resonances. When I cranked up the frequency to where it did resonate, I broke the wire bonds in some transistors and crystals before the capacitor started wiggling.

Incidentally, I also made tunable coaxial capacitors using brass tubing and teflon insulated wire. Same idea except that I rolled a detent near both ends of the tube, to compress the insulation, and still leaving it easy to slide the teflon wire in and out.

Minimal. Certainly none at 80 Mhz. Use the clear stuff and avoid the brown and orange flavors. If over

About the same as an equivalent length of wire. Add the connecting lead inductance which should be the same for both the gimmick and axial capacitors. For #24 AWG: I get 0.724 nH/mm. Series reactance at 80MHz: XL = 2 Pi f L XL = 2 * Pi * 80*10^6 * 0.724*10-9 XL = 0.364 ohms/mm

I haven't had much luck with gimmick capacitors in RF circuits. The problem is that the thermal expansion of copper with heating causes the gimmick to unravel. Twisting the wires together essentially puts the insulation under a slight amount of tension. When hot, the insulation softens and cold flows, changing the capacitance. This is aided by the copper moving around with temperature. Parallel wire capacitors and teflon insulation are more mechanically stable.

P.S. for normal AWG28 1.27mm pitch ribbon pairs, the capacitance will be about

C ~= 0.13 + 0.33*a pF/cm

where a is how much insulation is not hanging off the end (0

Exactly. You don't have to climb every mountain to enjoy the scenery.

One off-putting thing about the hook-up world is the number of STDs around, the good old classics and about 40 more incurable viruses of various nastiness. I've seen an estimate that 40% of twenty-somethings are carrying at least one.

Make sure your kids, male and female, have had all their shots.

Not handy, but the web site or a rep should know. It's free, and it's got a

--

John Larkin Highland Technology Inc

Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators

I'm only using an 80 MHz opamp here.

(Can't belive I just said "only 80 MHz.")