Topband: Amidon Beads

[K9AY]

>> When I contacted Amidon to order some of the new cores I
> found that the FB77-6301 only has a single hole and is not
> binocular.  They also said the don't make a binocular
> version made with type 77 material. [W7KW]

This is the right part no. -- I use a drop of super glue to make a 
'binocular' core using two of them.

> You would not want a 77 material, so I assume that was a
> typo. 73 material is about optimum in an application like
> this since it has an impedance peak at or near 160 meters.
> Have an impedance peak near the low frequency end of
> response minimizes the number of turns needed. [W8JI]

No typo, Tom -- 77 material makes excellent 160M transformers (as does 73). 
It was recommended to me by Fair Rite engineers when they introduced it a 
number of years ago, since it was developed specifically for inductor and 
transformer applications, rather than EMI suppression like 73 material. 
However, while some 77 specs look better than 73, I would expect the 
differences between them in a 1.8 MHz transformer to be small.  The newer 78 
material may actually be the best choice among Fair Rite's materials, but it 
does not appear to be produced in the same quantity and range of parts as 73 
and 77.

The price works out the same within a couple cents for one BN-73-202 vs. two 
FB77-6301, and the latter will have substantially more ferrite material, 
which improves low frequency response and power handling.

73, Gary
K9AY