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Inductors - RX Probs

Mark Jones <Mark@...>
 

Hi all

Looking for some help here.

Testing the RX today, AF amp clearly OK, the simple tests in the text work
out fine i.e. Touch base Q4 static, Q3 more static, Q2 less static. Trimmers
with L1,2 & 3 do little or nothing, but the trimmer in the T3 mixer has a
huge effect on noise out of the speaker. At either end of the travel very
loud.

It looks like there is no RF coming in. I have re-wound the two mixers with
no change, I'm wondering about the coils.

Here's what I have:

L1,2,3 22 turns 24 SWG on T-50-6
T1, T3 13 turns triffiliar 28 SWG on FT37-43

Any thoughts?

Mark Jones (G0MGX)
07971 091767

Jim Strohm <jstrohm@...>
 

On Jun 29, 2004, at 8:13 AM, Mark Jones wrote:

Here's what I have:

L1,2,3 22 turns 24 SWG on T-50-6
T1, T3 13 turns triffiliar 28 SWG on FT37-43

Any thoughts?
That wire is large enough that it should not have fractured within its enamel coating. For L1 - 3, an ohmmeter will confirm continuity.

For T1 and T3 -- this is worth asking -- did you use multi-colored wire for the trifilar winding to ensure proper connections and phasing? And did you check continuity before and after you soldered? A trifilar winding of #28 is much likelier to break without showing visible damage than the #24.

The only other possible cause I can think of is that the toroids are mis-marked and are so far from providing the right inductances as to make the circuit fail. If you can trust your supplier, this should not be a problem -- to test, use the mfg. data sheet to calculate inductance, place a 1 nF cap across the inductor's leads, and hit it with a dip meter. If it's a good toroid, it'll test within 10% of predicted inductance.

Jim N6OTQ