3280 and AD533 availability, EN frequency shifter

[Martin Czech]

:::I built the EN frequency shifter about ten years ago. I built it exactly as
:::published, with no deviations either in parts used or in circuitry (a rare

I have not build it.  But I may add that the (great) E.N. literature
research work on phase shift networks did one design aside (it is
mentioned, though), that is the polyphase network.

This network is passive and it was popular in the amateur radio world. (I
guess these guys go digital, today).  For our audio frequency needs we
don't need the rf transformers, 180deg phase shift can be done with
op amps.

The network has certainly the disadvantage of being expensive, because it
needs a lot of stages (each stage only 1.6 or so higher frequency). It
also has a bath tub magnitude response, which must be compensated. 

The advantage (that is claimed, I have no data so far), is low component
tolerance sensitivity, and no absolute but matching tolerance needs. Each
section has four resistors and four caps.  Ok, we can buy resistors with
1%, and on the same belt they often have actually 0.1%. This is easy
to measure. All resistors have the same value. The caps differ, but you
need only four matching caps for each stage.  No extreme matching between
stages. Caps vary with temperature, but matching caps won't vary much.
A decent multimeter has a cap measuring feature today, and even if the
absolute values are bogus matching should be ok.

And another pro: It is not E.N., so no copyright issue.
And dimensioning is straight forward, if you have a simulator.
The E.N. network is very difficult to dimension without the
given tables.

JH did once recieve a proposal of this network, I can not retrieve the
schematic today, since the schematic editor doesn't exist any longer.
Yes, Y2K!

If there is a need, I could do a copy out of the book and scan it.
If you have understood the principle, it is easy to adapt.

m.c.