Project is progressing, but I hit a bump in the road or I ran over
something.? :-)
First.? Because I wanted to try the higher frequency LO experiment
for the NC40A for changing IF to 9MHz and for other bands I wanted
to build up several rigs.? Easy.? Got the boards.? Got the parts.
Don't have the time.? You know the drill.
****
I do want to give away as many 4.096MHz crystals as possible.? I still have not seen
one person in this group come forward with how to beat the USPS
system.? Otherwise it is better for you to order 50 crystals off of
aliexpress.com and do you work and do it cheaper than the cost for
me to mail you a small matched set.? Life in the 21st century hasn't
gotten any easier.
****
You guys know about the QRPGuys.com digital display for $20 for either
PTH or SMD versions.? It is based on the work of DL4YHF and can be
found on the web in various places.? Doug and Ken got permission to
use the work for the digital display.? The Chinese use the same code in
the red PCB Chinese Crystal Checker and Frequency Counter, which this
group discussed a few years back.? The code is not open source.
Last night, for the 4.096MHz crystals, I got to the IF crystal filter
and needed to match the crystals.? Instead of taking time to setup
a matching system I did the following quick and dirty setup.? This
is based on a technique that is mentioned in the digital display
manual for the Guys.? If you subtract a different value from you
input RF frequency being read, you can gain some more digits.
You want to match crystals to 10-20Hz?? You need another RF source
or a crystal of the right value.? I'm matching 4.096MHz and I want to
remove the leading 4 from the display.? Easy.? I take a 4.000MHz crystal
and read its value in the crystal checker and store it in memory to be
subtracted from the crystals being checked thereafter.? Attached is
a photo (blurry) of the result for one of the crystals.? I turned off
the white LED lighting to get the desk dark enough to read and photograph
the display, but the exposure time went up and I moved the camera.? Should
have used a tripod or I have a clamp, but didn't think of it.? But you
get the picture.? ;-)
The display is showing 95.968KHz.? We know that it's KHz because the decimal point
between the 5 and 9 digits is blinking.? This means the display is reading
down to 1Hz!!? So, I quickly matched 4 crystals to within 5Hz. Because
I did not have to keep a record, I just took a pile of crystals and put
4 that read the same value into the IF of the NC40A.? It goes faster than
the time it takes to write it up.? I didn't need to kill a tree writing
down values for each crystal measured, sorting and pull the ones to be used.
So the difference between 4.000MHz (not really, but it works as I don't
need to know the value exactly) and the 4.096MHz crystal in the checker
is 95 968Hz (95,968Hz, but in some countries that is 95.968Hz, and now
we are all confused).? Get 3 more with the same value or very close and
the crystals are matched well enough for this project.
Eons ago I thought of the same procedure, but using the crystal with
the lowest reading in a batch and store its value and subtract. But,
the code will not do it and since it is not open source we can not fix
it.? Some one do an open source counter and let us all use it in a
matching system and I'll do the PCB.? Homework for you guys.
The bump:? Had to recalculate some L values for tuned transformers, like
T3.? Thanks Diz for his online calculator.? Here is how I use this valuable
resource.? Go to the FT37-61 toroid and you get a calculator. Feed it the
23T and 47pF value.? Hit Calc.? You get 4.302MHz as the tuned frequency.
Clear the calculator and put in 4.915MHz in the freq box and put 47 in
the cap box and you get 20T.? If you do 4.915MHz and 23T and calculate
you get 36pF.? The original kit had 39pF, which is much closer than the
current.? Some one can experiment for me, please.? You can see why I wind
up in so many rabbit holes.
The point.? Even if you buy a kit, you need to do some checking for some
improvements that you might find yourself.? I suspect that the value was
changed due to availability of parts and costs.? The reason will never be
known as the players are off doing other things or retired from the kit
business.
The other bump.? I have to sacrifice another NorCal40A and remove the
LM393 for this project and I have to find the poly caps for the VFO
to insure we are all on the same page in doing the drift tests. So
we'll be back sometime later with the latest news.? I don't seem to
have either C0G or NP0 values to use in place of.
Sorry for the delay.? Techies are working to bring the project back online.
FYI
chuck, k7qo, 'I may be slow but I'm ahead of you.'
