Hi Carl:
I have learned so much and realize
how much there is to learn. There is
a lot to tell which I will save for a
future report (which will be soon.)
Briefly, for now, Q2 was replaced and
I destroyed it a second time trying
different things. I went out to Radio
Shack and got 2 more 2n4401 transistors.
It takes a tremendous amount of drive
from my stereo amplifier speaker output
to modulate that second stage. I was
able to do it but I am interested in
some other modulation schemes, as you
are. (Maybe I'm doing something else
wrong.)
I was able to get a lot more RF out of the
second Q2.
More to report soon. This is great stuff!
Bruce, MICRO1690/1700
Open before me on the desk is Part 15 Frequency Table and Requirements.
15.225 states that the range 13.553 - 13.567 allows any type of intentional radiation limited to 10,000 uV/m @ 30m.
The 2nd harmonic of the center of this band, which is our experimentally active frequency of 13.560 mHz, is 27.120 mHz, which falls between CB channels 13 & 14, also allows any type of intentional radiation at exactly the same limits, 10,000 uV/m @ 30 m. Therefore our conjecture of possibly calling the 2nd harmonic a transmission in its own right is seemingly legal. Of course it would be necessary to send exactly the same audio over both frequencies, as no one has invented a way of sending separate audio over a harmonic. According to this rule even certain CB channels themselves are open for low power use.
The 3rd harmonic at 54.240 mHz falls just below VHF TV channel 2 and falls within 54-70 mHz, whose low power use is reserved for Non-Residential Perimeter Protection Systems requiring tight application of rules regarding harmonic suppression. The status of our 3rd harmonic is due for checking in the near future.
The 4th harmonic is 108.480 mHz and falls within the range 108 - 121.94 mHz whose low power limit is stated as Spurious Emissions Only 150 uV/m @ 30 m. Fortunately the filter on our experimental transmitter has completely crushed this harmonic and it is unreadable on a sensitive receiver at 2-meters from the transmitter.
Hi Carl and everybody else out there:
Would an amateur radio HF transmatch help
pull down the harmonics? Of course tuning
it correctly with just a few milliwatts of power
would be a new experience, but I bet I could
figure out how to do it. I just haven't had the
chance yet to buy any parts for a better
low pass filter, and I want to do experiments
without putting my signal where it shouldn't be.
Best Wishes to all
Bruce, MICRO1690/1700
I think the 27 MHz Part 15 field
strength is 10,000 uV/M at 3 meters,
not 30 meters, but I might be reading
it wrong.
Bruce, MICRO1690/1700
Thank you Ermi for the Part 15 info.
Bruce, MICRO1690/1700
Thank you for these head-openers. I am using the FCC OET Bulletin No. 63 Oct. 1993, which may be out of date. The figures as I gave them are exactly as stated in this bulletin, but now I'll look for more recent information.
Thank you.
The 15.225 field strength limit at 13.56 MHz is 15,848 uV/m at 30 meters. All of the Rules and Regulations are linked on the FCC web site.
M!CRO1700 reads the 27 MHz limit just fine.
Hi Everybody:
The ham radio transmatch attenuates the
second harmonic very well. I haven't had
any chance to check any possible higher
harmonics, but 27.120 is way down
(if that's what you want, I understand that
running that second frequency without a
second transmitter can be fun.)
Waiting for more parts and waiting to try
to figure out maybe another way to
modulate the power amplifier, I decided
to try experimenting with modulating
the oscillator again. Best voltage for
100 percent modulation is 2 volts,
anything lower and the oscillator
doesn't run. Anything higher and the
modulation gets weaker and the quality
goes down. Increasing the voltage does
make more RF, as expected.
With a sixteen foot quarter wave wire on
the floor of my kitchen (with nobody around)
the signal went several hundred feet down
the street on a Sony ICF-2010. But I can't
remember what voltage I was running to
the oscillator at that point. I have to keep
better records.
Best wishes to all
Bruce, MICRO1690/1700
MICRO1700 I'm thinking about your modulation trouble and recall something you might want to experiment with. The biasing of the base of Q2 has a huge affect on the blend of modulation and RF, and for my transmitter with 9vdc B+ the combo of 6.8k and 10k (as in my schematic) gave the best results of the several combinations I tried. Maybe the situation varies with different transistors.
Since Ermi Roos has been correcting us by noting that the allowed power level for 13.56 mHz is 15,848 uV/m @ 30 m (not 10,000 uV/m @ 30m) I have checked, and am using printouts of two documents with the 10,000 uV figure, both from the Ramsey website and both still posted on that site. They are FCC OET Bulletin 63 Oct 1993; and FCC 47 CFR Part 15 Rules 10-1-97 Edition. I'm assuming there are newer editions of the rules with different terms, and I'll be back as soon as I figure it out.
Some of us have been working from outdated copies of the rules. As far as this one issue, Part 15.225, here is the current rule
http://www.hallikainen.com/FccRules/2009/15/225/
The website shown here carries FCC Rules Updated Daily!
Carl: I think you are right about the
biasing. Your metal transistor (which
I think is an old 2N2222 is probably
a little different from a new 2N2222,
and I'm using a 2N4401, which is
again, similar, but not quite the
same. I will try different biasing,
but it will take me a while.
I think it was great that I was able
to modulate Q2, but I had to turn the
volume on my stereo amp up almost
all the way to do that. I don't want
to blow up my stereo amp, and
I use it all the time to listen to music
anyway.
Thanks for the info.
Bruce, MICRO1690/1700
MICRO1700 there are some audio amps, as I understand it, that must see a characteristic load of between 4 and 16-ohms or the output transistors can overheat and even fail. This happened to me once. To avoid that, you might want to add a 16-ohm (or there abouts) resistor with the appropriate wattage so your audio amp is protected. Make sure both left and right channels are loaded, even if only one of them is modulating your transmitter.
Since my original Q2 2n2222A burned out, which was before I succeeded in modulating, I've been using an odd transistor from spare parts - GE-20, which lists the same specs as the 2n2222A and is also metal top-hat type. It is no longer available, but was a replacement for Phillips ECG 123A, which may still be available.
Bruce,
Any chance you have the modulation transformer installed backwards?
Neil
P.S. my "personal thing" has been resolved so I can pay attention once more.
Thank you Neil, for the comment on
the modulation transformer. Well, I
tried it both ways, so I think it's
OK the way it is. It also agrees with
Carl's schematic with regard to
primary and secondary. It's good to
have you back, Neil. I'm glad things
became less complicated for you on
the home front.
And Carl, I will put resistors across the
output of the stereo amp and try things
that way. I appreciate the input.
Bruce, MICRO1690/1700
By the way, during an inspection how does the inspector determine the input power to the final?
The DIRECT and INDIRECT method.
INDIRECT= voltage x current x efficiency = power out
Example: 12 volts x .15 amps x .65 = 1.17 watts
DIRECT = P = I sqr x R (antenna resistance)
Example: 2 amps squared = 4 x 50 ohms = 200 watts
Hope this helps.