Hello,

I suppose this is kind of a dumb question, but looking through my old (circa 1931) QST magazines,
the readers occasionally refer to another operator as a "Lid".

I don't think it's a good thing!

Is anyone familiar with this lingo?

Thanks!

73

--KC9KEP

One word of caution when using a printer.

Printers are frequently *not* perfectly linear.

I've got bit on this before, both when creating front panels and
years back when creating PC board photo masks by using a printer.

The difference may be small (maybe 1/16" inch across a panel)
but it can gitcha!

--KC9KEP

2 additional comments ..

There were two versions of the Mighty Midget published by the ARRL.  The first was in QST magazine.
It indicated the two 1N34A type diodes in the detection circuit.

If memory serves me, the author stated that the diodes were arranged as a "voltage doubler" (as is
commonly done in DC power supplies.)

With no fan-fare, these two diodes dissappeared in the ARRL Handbook version of the same receiver
a couple years later, being replaced with a single 1N34A detector diode.

Also, just one more comment/question about the resistor/capacitor in the cathode of the audio amp ..

I thought that the plate resistance, cathode resistor, etc. set up the DC load line.  And, because
the paralleled capacitor "passes" the AC to ground, that the capacitor set up the AC load line?

Just curious :-)

73

--KC9KEP

Woops .. did I say I have a 200 MHz scope?  It's just 20 MHz. Tenma Model 72-320.

I'm working on my radio and not sleeping enough!

73

--KC9KEP

Alan,

Thanks for all the information and ideas!

I will try the high-pass filter idea tonight as well
as loosely coupling the signal generator to the antenna
input.

Yes, the local oscillator and BFO outputs can be easily displayed
on the scope by connecting the scope probe/ground to a loop
of enameled wire, consisting of about 5 turns or so.  These
induced signals can even be "read" by my cheap-o frequency
counter.  (I can calculate frequency using the scope (1/period),
but the freq-counter is easier and a bit more accurate :-)  )

And, yes .. I can drive a small (3" X 5") speaker from the
secondary of the output transformer, which is what I have
been doing (in addition to the headphones connection).

And, I see what you mean about the "omission" of any
bypass capacitor on that audio amp.  That capacitor
also sets up the AC-Load-Line, no?  And, maybe changes
the frequency response to add more "lows" to the audio
output?

Seems simple enough to sub one in to see what happens.

And thanks again, all.  This is the best part about home brewing ..
learning!

73

--KC9KEP

Hello all,

Thank you for all your thought, time, and replies!  Very helpful.

I made a huge faux pas in my original assumption .. I used "inductance"
instead of "inductive reactance" in my formula!

I feel like Chris Farley on Saturday Night Live; "Stupid!  Stupid!".

But, I guess that there's even more to this impedance calculation than
meets the eye.

It's "one of those things" that I was interested in understanding more about.
(Maybe one of those fancy Agilent network analyzers would reveal much more
about the input impedance?)

re: tracing through the RF amp circuit:

The problem I was experiencing was that the miniscule RF signal is riding
upon a huge AC power supply ripple, about 2V p to p (upon ~130 VDC).

The receiver sports a "cheap" DC power supply, half wave rectification and "PI" type
filter using a resistor rather than a choke.  I have a 200 MHz Tenma scope
that refuses to trigger on the RF that is riding upon the power supply
ripple .. even with the vertical amp AC coupled and the horizontal sweep speed maxed out.

I was wondering if I just need a better scope (I bought mine for $100 used)
or if a different piece of test equipment would be more appropriate.

The radio is working quite well, but I am very much interested in learning more
about the invisible nuts and bolts of how these circuits are quantified and
designed.

Thanks again all!

73

--KC9KEP (Tom)

N2EY,

Yessir, it is :-)  I did find some of the required crystals.  I've build several of these ARRL
designs in order to learn what they "handle" like and how they perform.

I've completed the radio to the point of operation, but it's yet to be mounted into its cabinet.

The crystal filters sound very "band-passy" if there is such a word.  I thought that perhaps
the narrow bandwidth would simply help eliminate the adjacent channel "interference"
(which it does) but it sounds suprising similar to the I.F. amplifier regeneration method.
(Or, Q-multiplier technique.)

I am currently in the process of trying different crystal combinations to achieve various
band pass width .. and, I'm listening to the effect on SSB, AM, CW, etc.

I am still adjusting the LO coil to get proper span on 40m.  My 80m is quite close.
(It cuts off a bit of the lower end of the band right now.)

The receiver works quite well so far .. fairly stable after a bit of warm up (it
utilizes 3 6U8 pentode/triodes)

And thanks greatly for the link to the data which I am seeking!

73!

--KC9KEP

Hello all,

Can someone help me to understand or guide me to a reference
that will explain how the input impedance of a receiver
is calculated/specified?

I am building a "new" receiver: the "Mighty Midget" as specified in the
late 60's QST and ARRL handbooks.

I wanted to apply a test-signal to the antenna input connection in order to trace through
the first stage of RF amplification.

I used a Heathkit IG-5280 signal generator.  Its maximum output (unloaded)
is about 150 mV P to P.

When I connect the signal generator to the antenna input, the RF signal
from the IG-5289 practically disappears.  Which isn't unexpected because the generator is
driving into about 14" of 26 Gauge wire, or about 6 turns around a 3/4" coil form.

If I'm not mistaken, these ARRL designs are intended for a 50 Ohm antenna.

So, I tried to make the impedance calculation by measuring the inductance and DC resistance.

Xl = 1.23 uH  and DC resistance =  170 m Ohms.

Then I thought I'd try the Pythagorean theorem calculation to get the hypotenuse
of the resulting impedance triangle.

Of course, the DC resistance completely swamps out the inductive reactance, so
my result is still about 170 m Ohms of impedance.

So, how is this calculation made?  Is it a more obscure calculation similar to the
characteristic impedance of a coaxial cable (the square root of "L" over "C"?)

For that matter, what sort of measurement device would one use to "see" such
a small RF signal that, in my case, eventually gets buried in the B+ ripple
when looking at the plate output of a pentode?

Thanks!

73

--KC9KEP

Hello all!

I am winding some coils for my new home-brew "Mighty Midget" QST receiver
that I'm building because I was unable to find the exact Miller coil required.

I have a few salvaged slug-tuned coil forms that I will be using.

I understand that the inductance of a slug-tuned coil can be increased
or decreased depending on the composition of the slug.

I also understand that high-frequencies demand a different core than low freqs because
the eddy currents and hysteresis losses become critical in high frequency applications.

And, the cores are color-coded, indicating their appropriate frequency range usage.

My question is:  What happens if I use a green core (or some other higher-frequency
core) for my relatively low frequency I.F./BFO of 455 kHz?

I guess I'll find out because I will use what I have, but I haven't heard much about
using a high-frequency core for a lower frequency application?

I am able to measure the inductance so, I'm not too worried about creating the wrong
inductance rage.

Would anyone have any thoughts on if this will work?

Thanks!

73

--KC9KEP

LOL!  Good ideas :-)

I wonder, in general, how one can cover their butt before sending money to someone that you
don't know.  I suppose if one writes a check, they could stop-payment on it should something go wrong?

73!

--KC9KEP

Hello all,

A ways back I placed an ad in the classifieds in eham. 
I was (and still am) seeking a metal radio cabinet.

I've got two replies via email so far and both seem *REALLY* fishy!

The first asked for $200.  I told him that I've seen metal cabinets at swapfests for as little as $3.00.
He quickly wrote back; "How about $150?"

I asked him if he had a photograph, and if he was a ham.

The answers were "no" and "no".

But, he assured me that the product worked really well!  (Hey, it's an empty
metal cabinet!  What's not to work!)

I didn't respond.  A day later, another "offer" came from England.
This time, they wanted $225.  Probably a shill helping me to decide that $150
is really a good price!  I could not locate the call sign of the "ham" from
England.

Has anyone any advice of how to sort out these frauds?  Has anyone else
had such an experience?

73!

--KC9KEP

Yes!  That was it! 

Thank you!

--KC9KEP

Hello all,

I thought I had seen a Behringer mic compressor/limiter mentioned on this forum, but I cannot seem to locate it again!

It was *not* a full-rack sized 18" unit.  It was a small box with LED's that indicated limiting or compression levels or both.

Does this ring a bell with anyone?

Thanks!

--KC9KEP

Here's another one:  "Plug" and "Jack".  The "Plug" is the male part that goes into the "Jack".  I've seen those two get mixed up all the time.

Or 73's which is like saying; "Best Regards's"  Or what is your QTH which is like saying; "What is your 'what is your location'".

And, here's another thing that bothers me!  Why do people say "ass trick" when they mean "asterisk".  The former sounds like something that
I don't want to elaborate on.

Or, people that say "irregardless" when they mean "regardless".  "Irregardless" isn't even a word!

Or, "pacific" for "specific" .. Or, "physical week" for "fiscal week".  Or, foo-pah for faux pas.  Or "I seen it" instead of "I have seen it".
Or, "I don't got no" for "I haven't any".  Or, vo-koo for beaucoup. 

Ayiee .. I'm melting down .. melting .. melting ..

73!

That's it!

Thank you ..

--KC9KEP