Re: Measurement Receiver Inductors

John Kolb

I was a manufacturing engineer for Southcom International back in the dark ages. We had the coils wound by a subcontractor (our production ladies working at home) and then adjusted them tighter or loser using Boonton Q meters. I was going crazy writing engineering change notices on the coil drawings with each new batch of cores till I was allowed to specify the winding instructions as + or - a number of turns. It was probably +/- 4 turns for a coil of 120 turns.

So yes, for critical applications, toroids have to be tweaked by squeezing or expending the winding around the core or even changing the number of turns.

We once received a coil from a commercial coil manufacturer where their wire spool had run out in the middle of the winding and another wire was joined with nice square knot on the insulated wire. Couldn't figure out how a single toroid could not have continuity from one end to the other :)


On 2/19/2016 9:23 PM, k5ess.nothdurft@... [PHSNA] wrote:
Wonder if others have found that the inductors called for in the
Measurement Receiver need tweaking? I found that the inductors in the
impedance matching networks at each end of the crystal filter needed one
less turn (11 vs 12) and needed for the turns to be all scrunched up to
arrive at a value close to 8.05┬ÁH. Value was determined using the
Crystal Test Fixture and measured known capacitors.(This is another good
use for the Crystal Test Fixture). Still, I can't see any difference
when tuning the variable caps associated with the matching networks at
each end of the filter. I modeled the matching networks in LTSpice with
a 600 ohm 6dB pad between them and the response is pretty broad. So are
the variable caps even needed? I'd be interested in others experience.

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