I forgot about CB for years, but now that it's in the headlights, I think it could be a tremendous tool between neighbors, among family members, and for general fun. People are really missing a golden opportunity by not knowing about it. I'm thinking about building two CB stations and handing one over to a neighbor so we can talk back and forth.
I'm glad you mentioned radio control, I wasn't thinking of that. But is that that only for toys? Is there any chance radio control channels are used on some business or government level?
Hi Carl: I think the "in between" channels on
CB are mainly for just radio control of toys. There
is also a 49 MHz channel that is also used for
toys. Off the top of my head I don't think the
the 27 MHz channels are used for much else.
I have always wanted to get into radio control
of models, but have never had the time.
I have looked at some of the websites for that
hobby, though and they are really interesting.
I think most people who are really serious RC
enthusiasts use 72/75 (?) MHz. A lot of ham RC
people use 50 MHz. It's around there anyway.
If you look at the RC websites, some of the
model planes are HUGE. If a person was hit
with one they could be killed. So I wouldn't
trust 27 MHz for a serious RC model. But a
little toy car or a small flying vehicle (my son
has a little styrafoam (SP?) RC plane)
for instance, might be OK.
I really liked CB radio when I was a kid. At that
time people were using callsigns. I even had a
CB license later on. The upper CB channels where
sideband transmission is used could be very very
useful. The problem, as you know, is skip, and
the occasional person running a lot of power who
may have an unconventional agenda.
If I can get this 13 MHz transmitter running, I
will probably make another one for 27 MHz for
the experience. The range is so small, I can't
see it hurting anything. If it goes 500 feet on
one of those "in between" channels, I don't
think anyone will mind. Also, I have no idea
if business or government would use RC there.
I'm bet they can think of better places in the
spectrum to go. This is interesting stuff. I
think I'll look into the spectrum use of these
ranges a little deeper.
Best Wishes
Bruce, MICRO1690/1700
P.S. I just looked at a list of RC frequencies.
It was a big list. There is a footnote there
that recommends that the 27 MHz RC channels
should be just for cars and boats.
O.K. you got me thinking aloud here. Let's say we have a part 15 transmitter on a remote 27 mHz frequency. Well, somebody with a toy car transmitter wouldn't hear our transmission because they have no loudspeaker. Can we assume that our speech & music audio will leave the toy car undisturbed, and not make it shift into reverse and back off a mountain? And wouldn't it be likely that if the toy operator sent remote signals to run the car, their carrier would override the part 15 signal and the car would operate just fine?
Hi Carl:
Well, right now we don't know the practical
range of a Part 15 27 MHz "broadcast" that is;
10,000 uV/m @ 3 meters. If the 13 MHz
strength is 15,848 uV/m at 30 meters, and
that's about a milliwatt or so into a dipole
(approximately) then the 27 MHz "power"
sure can't be much.
I looked at a bunch of R/C websites and they
are really fun. It seems that the frequency
for most of the RC toys is 27.145. I
think we are talking about Part 15 transmitters
working with inexpensive regen receivers that
are pretty deaf.
I was surprised to find that there are more
expensive serious systems that are channel
switchable and use FM and these are on 27 MHz.
My only interest in these bands really (aside from
experimentation, which is great) is that I have
a friend a mile away who is a ham and an SWL
and he could listen to my station in his house
with his good receiving setup. I guess maybe
if I was trying 27 MHz Part 15 broadcasting I
could, for instance, only run it at night.
But I don't even have the 13.560 transmitter
running yet, although, the modulator is about
halfway done, so this 27 MHz stuff is still
just theoretical.
Best wishes
Bruce, MICRO1690/1700
P.S. I guess in answer to your question, the
chances of a Part 15 27 MHz radio station
broadcast interfering with an R/C device
would be very small.
My USB wireless keyboard/mouse system is on 27 mHz.
Hi MRAM1500:
Oooops! I forgot about those wireless
keyboards. Wow! I would love to
tune it in on a receiver and hear what it
sounds like. Can you even do that or
is it spread spectrum or something like that?
Best Regards
Bruce, MICRO1690/1700
Hi Everybody:
The modulator board for the 13 MHz transmitter
is wired up. This board uses two 2N4401s and
a bunch of other parts. I have checked it a few
times and have already found a few wiring
mistakes. I have fixed those and will be checking
it several more times visually before I insert it
into the transmitter B plus line. I also still have
to replace Q2 (the transmitter RF amp) which I
have blown up twice. I am going to do this all
very slowly when my mind is fresh...
I wonder when that will be? (Only kidding.)
Bruce, MICRO1690/1700
Hi Everybody!
I built a 2 transistor (2N4401s) modulator
for the Talking Pixie transmitter and it
didn't work. I was very careful, but
because of my poor eyesight almost
anything could be wrong.
Even though it didn't work I had a good
time building it. The 13.560 MHz AM transmitter
project is still alive here. The idea of having
a transmitter running on that frequency is too
much fun to stop work on it.
When I have more info about this and anything
else related to it I will post it here.
Best Wsihes
Bruce, MICRO1690/1700
Hi MICRO1700
Disappointment with the transistor modulation not working. What I hope you can do is analyze the job and see if you can discover what may have been done wrong. Maybe it's fixable.
Things have ground to a halt here since I want to suppress the 2nd harmonic at 27.xxx, which I haven't worked on yet.
There may be one or two more SW projects coming up: I have a 3-transistor schematic that looks interesting, with oscillator, buffer and final stage, and I'm planning on using that direct modulation method with it, which has already proven successful in a past experiment.
Hi Carl:
Thanks for the kind words. I intend to keep
moving ahead on this 13.560 transmitter.
I'll just keep trying other things until I
come up with something that works. I
certainly welcome everybody's input. As for
myself though, I don't have any intelligent
questions to ask yet.
Best Wishes
Bruce, MICRO1690/1700
P.S. Carl, good luck with that 3 transistor schematic.
Hi Carl and everybody:
As you all know, the transmitter Carl and I
have been working with is a two stage
transmitter.
Just as an experiment, because my second
stage is blown, and I haven't had time to
replace the 2N4401 yet, I did some experiments
with just the oscillator again.
I have been able to obtain a power input range
(depending on supply voltage) from 50 mW down
to a few mW. Current drain is very low. The
transmit signal sounds clean. (I tried putting 2
transformers together and get enough audio now.)
The transformers are driven with a little battery
powered (9V) amplifier that is very small - actually
you can hold it in your hand. The modulation sounds
clean - it is not FMing at all, it is just AM.
Although there are lots of RF harmonics, my ham
radio transmatch attenuates the second harmonic
very well. (I have not listened to the higher
frequencies yet.)
If you guys have any comments on this, let me
know.
Thanks
Bruce, MICRO1690/1700
MICRO1700
If your final transistor is blown, how could you possibly be getting audio modulation?
The final stage of the transmitter is not modulated. Many high efficiency AM BCB transmitters are not modulated in the final stage. Try researching the Collins Ampliphase transmitters. Some of the new HD AM transmitters are modulated in low level parts of the box.
Granted, it is possible to modulate an AM transmitter at an earlier stage, but my curiosity centers on the fact that the Pixie2 schematic shows final stage transformer modulation at the collector, so I wonder how the Q1 circuitry has been altered to allow modulation.
You guys are great! Thanks so much for the
comments.
I did put the transformer (transformers) in
a different place to modulate the oscillator.
But I'm going to back up for a second.
All I wanted over the holidays was a 13.560
signal on the air just for the fun of it. I was
pretty much just looking for a yardcasting
set up.
I had built a 2 transistor (2N4401s) modulator
that didn't work. I may have reached the
limits of my eyesight because I had a lot of
trouble seeing what I was doing. (You can
only use so much light and magnification.)
(Briefly, just for background, I was born
prematurely in 1954, and my retinas and
optic nerves were seriously damaged.)
So I chucked the 2 transistor modulator for
now. I inserted a modulation transformer
in the B plus line to the oscillator and took
the RF out from the end of the first stage.
(After the coupling capacitor.)
The first transformer (1200 ohms/3.2 ohms)
worked but only with very low voltage. With
the 1200 ohm side in the B plus line I got
good modulation with about 2 volts to the
oscillator but very little RF. Also the output
admittance from Q1 is unknown. As the voltage
was increased from my variable supply the
modulation got less and less, which is to
be expected. I cut another transformer out of a
radio I use mostly for parts. This transformer is
120 V in, about 12 volts out. I inserted the
second transformer into the B plus line to the
oscillator, and I fed it with the first one. I was
able to get 100 percent modulation with a
higher supply voltage (somewhere between
5 - 9 volts.) This also gave me more RF.
I had to do all of this quickly, because of
holiday activity, so that's why my supply
voltage figure is not exact.
The modulation was 100 percent at 5 - 9 volts
I fed the
transformers with a little radio shack amp.
You guys may have seen these little amps.
You can hold the amp in the palm of your
hand. It has a little grey case and runs on
a 9 volt battery. The modulation was lacking
in the low end of the audio range, but at
this point I am not concerned about that
as this is just an experiment.
At this point I was only able to measure RF out
in a relative way. I have a ham radio field strength
meter that is also an SWR bridge (a really cheap
one that probably cost 20 dollars 20 years ago.)
This unit has a whip antenna for use in the field strength
meter mode. When I touched the antenna to the
output of Q1 (at the far side of the coupling cap) the
needle slammed to the right side of the
meter. This was at about 12 volts from the supply.
I don't remember the current drain figure. At this point
modulation was about 50 percent but around 5 - 9
volts modulation was good. There was still a fair
amount of relative RF indication on my little meter.
I have to get the scope out and take some real
readings. (As you guys know, my Part 15 operation
is more of an experiment. My station actually isn't
on right now. I plan to put the AM BCB transmit
antenna back up in the spring and go back to
continuous operation then.)
In a separate experiment I inserted a ham radio
antenna tuner between oscillator RF out and
the antenna. This experiment was done
several weeks ago with about 2 volts running
to the oscillator with 100 percent modulation.
After basically tuning for max on 13.560, I
found the second harmonic (27.120) was
way down, although i don't have any exact
figures. The antenna in that experiment was
a 16 foot wire laying on the floor.
I have only scratched the surface regarding
the experiments that can be done with this
little 2 stage transmitter. My eyesight is a
limitation. It takes me a very long time do
do things.
So I will keep experimenting, and I will give
you guys reports on this.
Thanks again for your input. I appreciate it
very much.
Bruce, MICRO1690/1700