[AMRadio] Items For SWAP...

[Brett Gazdzinski]

Eddy,
I likely have them, but you may get many replies.
I could send them for nothing, if I have the correct size.

I think its much better to work from the antenna input and work the other
way,
but I have a nice spectrum analyzer to help.
Building a homebrew superhet of any type is very hard without
info as to what is going on!

The spectrum analyzer allows me to look at frequency, amplitude, and signal
types all at the same time.

Build an antenna input circuit, and look at the amplitude out, the
bandwidth,
etc.
Build a LO and look at the amplitude, harmonics, stability, frequency
range, stability.
Build a mixer and look at output noise, signal strength.
Look at filter operation, bandwidth and quality, center frequency,
loss through the filter.

I had problems with my 2nd receiver, the 2nd if stage oscillated
VERY well, and nothing would stop it.
I had to change to 6BA6 tubes in a different design to get rid of it.


I built the detector last night, and things were working well, till I
changed to 40 meters. Then I got all sorts of odd behavior, and spent
an hour tracking things down. Signals sounded like a BFO was on, and I found
the antenna coax had a bad ground (loose) connection at the cabinet.
It was picking up general noise and hash from the MFJ power supply that runs
the
Icom 756pro.

Building receivers is quite different than a straight forward transmitter
or modulator. Small signal RF can do crazy things in all sorts
of components, not enough shielding, different component types can cause
oscillation, feed through of signals can effect things a lot, etc.

I think I still need to do something better with the antenna input,
the large B+W coils have high Q, but likely pick up all sorts
of signals all by themselves.
I may try shielded coils on slug tuned forms, with a different circuit
maybe.
Every receiver is different, and has its own problems, it likely took a lot
of
design time to make a commercial receiver, every part likely had to be
located
and wired a particular way, along with less critical design types....

You need a modulated RF generator, and inject the signal into the IF stages
working your way forward.
It may be a LO or mixer problem.

Have fun, looking forward to the pictures,

Brett
N2DTS


>
> Greetings All,
>
> I came up two items short here in my 1929 homebrew replica
> superhetrodyne
> receiver project, specifically, two ceramic plate caps for my
> 224 globe
> tubes...
>
> Does anyone have a pair they'd like to part with...? They can
> be either
> National Radio type, or James Millen---as long as they're
> both white, glazed
> ceramic & presentable, I don't care.
>
> I'd be willing to trade TWO of my National 813-sized ceramic
> plate caps
> (i.e. R.F.E.---"Removed From Equipment") for your two
> 807/224-sized ceramic
> plate caps.
>
> Anything out there...?
>
> BTW, the behemoth is done---but NOT working (naturally!). The
> audio stages
> are FB, but little else. NOW comes the learning process...!
> I'm working
> backward from the detector stage on up to see what gives.
>
> It is one HEAVY mutha'! Good lookin', too, in a roaring 20's
> kind of way.
> Sure does look like it's hiding a lot of potential from
> me...with any luck,
> I'll be able to unlock its secrets BEFORE the 1929 QSO Party...!
>
> May have some digital pix taken & available on the weekend,
> too, in case
> anyone is interested---but I HATE taking shots of non-working gear...
>
> Thanks & my very
>
> ~73~ Eddy VE3CUI - VE3XZ
>
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