Re: Testing the Measurement Rcvr

Nick Kennedy

It's been 4+ years since I built mine, but I have some notes, fortunately.
Your idea of testing in sections is certainly a good one. I had to do a lot
of troubleshooting, although not generally due to the design or concept but
due to having a couple of bad mixers.

Also, I made a lot of changes so I had to be sure I'd done them correctly.
I used some 5.528 MHz crystals I had on hand so that changed the operating
frequency, the diplexer, the L-matches and so on.

Shooting through the crystal filter and its L-matchers before connecting to
the rest of the world is definitely a good idea. And since you have that
nice PHSNA instrument sitting there, why not?

I like to measure my critical component values pretty closely and also
simulate the circuits in LTspice, so sometimes I don't actually feel the
need to adjust trimmers. My notes say I pre-set my L-match trimmers to the
required value. But I could see plotting the filter curve and playing with
those trimmers until you got a nice flat response curve might be a good

I substituted an ERA-1SM for the ERA-3+ which changed other component
values a bit. It's easy enough to verify the gain of that stage acting
alone before installing the mixer.

For whatever reason(s), I didn't feel the need for so much oomph out of the
output amplifier so I changed the biasing to reduce standing current to
about 10 mA and didn't need a heat sink.

I did take a look through the diplexer before connecting it to the driving
and driven stages. I had already modeled it on LTspice and seen that, by
design, you don't get sharp peaks but you do get a constant load over a
wide range of frequencies. Which I guess is its function.

So getting back to testing in stages. Yes, especially on through-hole board
projects, it's a great idea. Sections can be hard to break apart after the
fact. And as I guess I've suggested already, you could easily build and
test separately the MMIC amplifier, the diplexer, the crystal filter plus
matchers and the output amp. Or combine the output amp with the filter.
This can be accomplished by holding off on installing the mixer until last,
testing the boards separately, and maybe keeping C15 out until you've
tested the filter and output amplifier separately.

On the fuse and blocking diode - your proposal to share them seems
reasonable. I don't remember exactly what I did there.

73 & good luck with the project,

Nick, WA5BDU

On Tue, Jan 1, 2019 at 6:40 PM Nigel Maund <maund.n@...> wrote:

Dear PHSNA testing community;

I am finally building the Measurement Receiver.

I wanted to ask advice on how to test/tune it as I build it in sections?

Here are my thoughts:

1) using the PHSNA, sweep the Xtal filter alone, and adjust the trim
capacitors to get a flat response curve
2) add the 2n2222 Amplifier, to then see the sweep with a 20 dB gain

Next steps - how would I make sure that the Bridge Tee Diplexers are
properly tuned?

Is it simple enough to wire up all the components and go for broke.
Or, is there a way to perhaps add in the Diplexer circuit and sweep it
using a 3.2768 MHz (spare crystal) oscillator,. If I were to use a return
loss bridge would this then give me some interesting way to use all the
test components and actually see the Diplexer working?

I am thinking of how best to test each of the two boards separately, using
the PHSNA and Power Meter, before connecting them together.

One final question: the schematic shows only one power connection
circuitry (200 mA resettable fuse, shotkey diode) but both boards have PCB
locations for this circuitry. Is it acceptable to simply wire one board
with this circuitry, and jumper the 12 volts supply to the 2nd board. Or,
do both boards need a 200 mA resettable fuse?

Nigel, Va2NM

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