MICRO1700 I enjoyed your report on how you modulated Q1 and seemed to have promising results.
While you were doing that I did some work on reducing the 27.12 mHz 2nd harmonic, which, as I've reported, can be received 1 1/2-block away on CB Channel 13.
If you think of my schematic, which I linked earlier, I've replaced L3 with the 13 mHz filter also linked elsewhere. In my drawing I left spaces where C6 and C7 would have gone, because I assumed the filter replaced those.
I placed 270 pF in the C6 spot, but it did not change the 22.12 mHz output. However, with the 270 pF at C7, directly at the antenna output, the signal seemed to jump forward as if it had reached a better "Q." Next I listened to 13.56 mHz with the 270 pF at C7, and the noticeable change was less, slightly detectable.
Does anyone agree with me that maybe a tunable capacitor at C7 might allow tuning for "Q" at 13.56 mHz?
Hi Carl:
I don't really know, but I think Neil
mentioned using a tuning cap somewhere
along the line in this thread. When I
used my ham radio antenna tuner
in the line I had to tune it to get max out
on 13.560.
I'll have to think about it. When you tune
a circuit that is feeding an antenna, by it's
very nature you would be increasing the
Q when the whole system hits resonance...
Am I right?? Hmmm. Maybe I'm not right.
Bruce, MICRO1690/1700
If it is warm where you are the rest of us would like to drop by for the next week or so. We are wearing everything in the closet and it isn't enough.
With shivering hand, I tried a 470 pF at the RF-Out of Pixie2 in place of C7 and, comparing to the last test described just earlier using a 270 pF, this time the 2nd harmonic at 27.12 mHz is perceptibly less and the fundamental at 13.56 mHz has jumped "forward" just a bit as if reaching resonance. The modulation is extremely pleasing from a small radio, the whole audio spectrum seems to be bright and present.
When I find more caps I'll try 560 pF and just maybe .001 uF.
MICRO 1700 I think I found your audio amp at Radio Shack, if it's Part # 277-1008C. It lists the output power as 200mW, which is probably why you got such low level at first. I am using a 3-Watt amp, but rolled back to about 1/3, so I'm probably driving 1-Watt.
It sounds like you compensated by double step-up transformers, and that's interesting. I wonder how much step-up there would be with an infinite number of step-up transformers?
I have an older version of that little amp, but I never thought of using it for this project.
We're on a roll here in the center of North America where the Arctic meets the Antarctic.
This question. My pixie2 homemade has yet to be mounted in a finished box. I have a plastic box, but read on a ham site that little transmitter projects should go into metal boxes.
Ya but, SSTran, RamseyAM25 and others are in plastic boxes. What do the certified transmitters mount in? (Rangemaster, etc.)
What advice is there?
Hi Carl! I just read your posts. I wanted to
type in this idea and then I'll probably have
more comments to follow.
I have a friend ham radio friend in New Jersey.
He loves vacuum tubes. And he builds all
of his projects in metal cookie tins, spam
cans, and that sort of thing. His transmitters
and receivers are beautiful works of art and
they work really well.
Since your transmitter involves audio stages,
you might want to put it in a metal cookie
tin or something like that. I think it might
help cut down on hum. With your background,
I'm sure you are used to working with metal.
You just have to be careful to not bend the
metal when you are drilling through it or
punching through it. Actually you have to be
very careful. You also have to watch your
fingers so you don't cut them.
You can use the whole cookie tin, or whatever,
as ground. You can solder ground wires right
to the inside of the tin, and you will have a
great ground plane on the inside.
If you have ever heard of a ham radio transmitter
called the "Tuna Tin Two" - well, it is a simple
morse code transmitter that has been popular
for decades. Hundreds have been built by ham
radio operators. And the enclosure is just a
tuna can.
Again, just be really careful because you are working
with thin metal. You don't want to get cut somewhere.
I have not done this myself because of my eye
limitations.
Well, it's an idea anyway. Maybe it's not best for
outside but you could put something else around it.
I think you did find the correct little audio amp that I
have from Radio Shack. Two hundred miliwatts
sounds about right. I have several of these little
amps that I use for various purposes.
I haven't had time to work on the 13.560 project
this week. I have to get my frequency counter
out and make sure I'm really on 13.560.
My plan is to put the transmitter in my attic and
feed it into a dipole. Audio will be supplied by
a radio tuned to my station. I believe a vertical
antenna would probably be better, but this will
be the best I can do for now.
Regarding the transformer experiment, I think I
was just lucky hooking those two together. The
power supply transformer I ripped out of the
radio is an unknown. I placed the little 4 Ohm/1200 Ohm
(or whatever it is) first after the amplifier. It was my
feeling that the bigger transformer ( the 2nd one)
could better handle the B plus current.
I live in Connecticut. It is cold here too. A few days
ago we had refreezing ice on top of snow on top of
refreezing ice. The wind was blowing like crazy.
Best Wishes
Bruce, MICRO1690/1700
P.S. I probably said this before. I have a friend with
a good shortwave listening setup a mile away who
tries to listen to my station when it is on. This 13.560
transmitter is being built so he can listen to my station.
Also, I'm glad you are having good luck with your
harmonic suppression. That's great!
Carl,
Bruce's suggestion re tin pans is good. They are cheap and easy to solder. I have made shielded receivers by clam shelling them fastened together with sheet metal screws.
Metal enclosures serve a couple of electrical purposes. One is to keep unwanted RF and electrical noise from radiating into the electronics. For example, my Ramsey FM25 has a lot of hum when mounted in a plastic box but none when mounted in a metal box. In most cases the metal shielding is more important for receivers than transmitters though even transmitters can pick up unwanted signals.
Another is to keep unwanted signals generated by the transmitter from radiating. For milliwatts this is probably not too much of a concern but for higher power transmitters with output filters the metal keeps the harmonics from radiating.
One thing to keep in mind is that the metal will add stray capacitance to the circuit so final tune up should be done with the circuit mounted in the box.
I have been away from the keyboard for the last couple of weeks and am pleased to catch up on your progress.
Neil
Thank you MICRO1700 and Neil for the comments. Here goes some spam and tuna meals. Back "when," I built my own audio console for my startup audio business and made a living with little 12AX7 audio tubes mounted on cookie tins. The enclosure was wood, but lined with copper screen and aluminum tracks to "rack mount" the tin circuits inside. The front was a solid 1/8" aluminum about 5' by 2' attached by door hinges. Nice VU meters and big knobs made it look official, so nobody ever thought it looked cheesy. The sound it produced was everybit as good as solid state sound.
In this cold I don't want to use solder because the smoke would be trapped in the air so I'm on hold until the globe gets better weather.
Hi Carl, Neil, and everybody:
Carl: Wow! That homemade board sounds
wonderful. I have a friend who did something
similar about thirty years ago, but it was
solid state. It wasn't shielded like yours, and
was made of wood, not metal. It did look great,
though.
I have a Gates Studioette board that I want to restore
some day. It is a wreck. I'm really glad to have it,
though, it is a piece of broadcast history. I have taken
most of the insides out. I have an intense desire to
rebuild it, because I have always wanted a real vintage
broadcast mixer. Oh, well. One of these days...
Oh, it is version number three from the 1960s.
It's funny you mentioned soldering in the cold. I just
bought a gigantic soldering iron for working on my
AM ground system when I get around to it. That will
probably be in the spring or summer when it is hot.
That's why I had to get a powerful iron. I have
sixteen radials that all need reconnecting. Next door
I have a neighbor who is 80 and he watches everything
in our neighborhood about 24 hours a day (or so it
seems). He watches me pulling wires out of the ground.
Then he goes in his house and watches me through the
window. Then he comes back out, watches me some
more, and then drives away in his car to pick up missing
golf balls next to a golf course. Then he come back and
watches me some more. Then he goes in his house, has
a beer, and watches me through the window.
Fairly recently, in the fall, I started working on my ground
system at night.
Best Wishes
Bruce, MICRO1690/1700
P.S. One way or the other, I plan to have 13.560
running in a few weeks.
Maybe you should make a friend out of your watchful neighbor. In these weird times he might report you as "suspicious" for wiring something in the ground. You might end up on a "watch list" and have clicks on your telephone. Take him an extra six-pack.
You could make a very neat new mixer from your Gates, which would be the focal point for your station.
Little mixer circuits are less complicated than building a transmitter, and modern "pots" will work fine. If you still have the knobs maybe they'll fit the shafts of the newer parts.
If you are looking to rehab a vintage console, try the components pre-built and available from Radio Design Labs. They are reasonably priced and work great. I have rehabbed several vintage mixers with these beauties.
Please move to vintage equipment thread.....
Thanks so much Carl and Marshal:
Carl: Maybe I should bring the guy
next door another 6 pack.
Marshall: I didn't know there was
a vintage equipment thread.
I'm going there right now!
Thanks again, guys!
Bruce, MICRO1690/1700
Hallo from a new member!
Being a sw-listener in Germany and interested in electronics, I constructed a 13.560 kHz oscillator a few days ago. Today, I found your website. So, anyone who is interested in the construction plans, fotos of the item and so on is invited to copy them. I can mail them per e-mail. Free, of course.
The oscillator contains two transistors. I used a tin housing, but this time it was not from canned fish. The first of the transistors is connected to the crystal, and you can easily adjust the frequency as accurate as +-10 Hz with small tuning capacitors. The secons one is used to avoid changes in frequency if anything is connected. A coil plus a capacitor is added to filter second harmonics.
Is anyone interested?
greetings from Germany, Georg
Hello Georg:
I think several of the members will be interested to see your schematic. Thank you for offering to share. Is there a central download spot you can post, otherwise I guess we''ll have to give our e-mail addresses one-by-one (?)
Dear Carl,
sorry, that idea with e-mail was not very good. So yesterday I prepared everything. I added a new page to my homepage. On this page now I am presenting five files for download: .bmp schematics, .txt description and .jpg fotos of the hobby 13560 kHz quartz oscillator and of a little filter to enhance the visibility of second and third harmonics on the oscilloscope screen, furthermore screen fotos of the oscilloscope showing the 13560 kHz signal. Everyone who wants may share my experience with these hobby electronics and download these files from my homepage. Afterwards, I wrote a comment here and gave the exact location of the site.
Sorry, but it did not work.
My account to part15.us has been blocked, my comment has been removed, and someone wrote something that hurts. I may be a little bit stupid, because I do not understand what I did wrong offering free downloads for hobby purpose.
Maybe you find a way.
Georg N.