Re: [IRCA] Cable work

["Craig Healy" <bubba@xxxxxxxxxxxxxxxxxxxx>]

> "What I didn't do is space the
> toroid so it was centered in the box, nor were the windings exactly
opposite
> to each other on the toroid."
>
> A retired electronics pro that I know tested xfrmers with  a spectrum
> analyzer with built in tracking generator and discovered that he had
losses
> above 1000 kc on his transformers with opposing windings on J or 75 mix.
> His best results occurred with the secondary windings centered on top of
the
> primary, overlapping.
> His test results were outstanding from LW up.

I have read a few studies on this.  Most do seem that overlapping the
windings did work, but another said that windings on the opposite side of
the core had better isolation.  It also said there was more loss, as the
magnetic field "escaped" the core between the windings.  I've put
transformers together both ways and never really noticed much difference.

One thing I can do is take a reading on a couple of stations, then move the
windings on the toroid, or move the toroid in the box to see if it makes any
difference at all.

The boxes I buld for the dual RG-58 quasi-balanced line will be trifilar
wound.  We'll see how that does.

> For a transformer, I have followed Gary Breed's (k9ay) method of using two
> FB77-6301 Ferrite beads epoxied together to make a small bino core.  9
turns
> of #24 mag wire and 3 turns for the RX side.  I saw his note on topband.
> My buddy tested this core and found MW performance to be very good, but LW
> had more losses than the 114J or 75 core.  While the small twin bead xfrmr
> did not measure quite as good in the MW band as the toroid core, one would
> not notice the difference at the headset.  These beads are quite small in
> comparison with the 114 cores and cost $5/dozen.  The FT 114J's are $3.75
> per. http://www.amidoncorp.com/pricing/  If you are looking for a more
> compact transformer for strictly MW, the beads are the way to go.

Much of my listening is done in very high RF environments.  Small cores
might saturate and cause trouble.  That's one reason why I use much larger
ones.  The FT-290 cores probably are good for close to a kilowatt, depending
on the circuitry.  Other than price, I don't believe there is any real
advantage to a small core.  Space is not a premium in the boxes I use.  I
rather like the FT-87-J size core.  Easy to work with, and room for whatever
turns I want to use.  I tried some small cores salvaged from an old Harris
transmitter board.  They filled up at about 14 turns.  Ugh..

I picked up a 50' roll of chicken wire today.  Under $20.  When the showers
stop, and I get some time, I'll run out the 150' length of RG-58.  A scan
will be made, and some notes taken of S-Meter readings up the band.  Then
the chicken wire rolled out over the nearest 50' of coax.  I'll see if that
makes any difference whatsoever.  And, I may put in a ground rod or two to
see if that helps.  If there is a difference, I'll buy two more rolls of
chicken wire and see if an end-to-end shielding makes any difference.
Oddly, it's called "poultry wire".  Is chicken wire somehow politically
incorrect?  I didn't realize there was a political action lobby for
chickens.  Gallus Group, indeed..

Craig Healy
Providence, RI

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