From: John Welch (firstname.lastname@example.org)
In response to the great discussion here and in
rec.radio.amateur.homebrew, I've decided to try a phasing receiver
just for funsies. I'm almost done with the one described in the
Signetics databook (using 2 NE602s, some op-amps, a 4053 and a bunch
of high-precision caps and resistors).
The 'heart' of this is a broad-band active audio phase
shifter, requiring 12 10K resistors, 6 1000pf caps and a few other
resistor values. Supposedly, for best results .1% parts would be
For the 10Ks, I got lucky. The engineering stockroom has (had
:-) some 10K 0.1% resistors. The 100pf caps I got by matching from my
pile of sm 5% caps - matched to 4pf according to my cap meter. The
other resistors are 1% values.
The rf is generated in quadrature by a 74F74 flipflop dividing
down a 48MHz signal to 12MHz. I may be able to get a better looking
signal if I change my 74HC14 to a 74F14 (an attempt to better square
up the 48MHz signal). From scope and spectrum analyzer, the signal
looks lousy. It *is* 12MHz, but has little resemblance to a square
wave - more of a rounded ramp. I'll try it this way firstm and if I
can find a 74F14 I'll try that too.
The main reason I'm using a 12MHz if is that I have built a
9-pole crystal filter at that frequency, to add ahead of the phasing
if strip if needed. Methinks it will be heavy overkill, but between
the filter and the phasing I expect to get rather decent selectivity
The front end will probably be a bandpass filter followed by
an SBL-1, with my trusty DDS signal generator providing the LO (after
some additional amplification required to drive the SBL-1 of course).
With luck, I'll have a reasonably bullet-proof front end.
For testing purposes I'll only build it for one band (40, 30
or 20 depending on the parts I don't have for the bp filter). I hope
to have it kludged up this week, and I'll let y'all know how she
flies. If she flies well, I'll try to get dork-cad to put out a
postscript file and enter it here. Stay tuned for more details.
-- John Welch, N9JZW
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