Which reminds me, certain portions of the 11 meter band are considered part 15 though the field strength is a bit more the band has it's own problems with hi-powered illegal amplifiers and foul mouths.
Then again, what a better way to clean up that band then to place a radio station there, even that could operate in the ssb mode.
I would love to hear a ssb station on shortwave operating as part 15.
The reception reports would probably start pouring in from all over the globe. The more I think about this the more i want to add 11 meters to my part 15 broadcast station. I already have a cb radio in my mini-van that hardly gets any use. 4 watts would go a long way and can be had for $40 bucks at walmart.
SSB on 11 meters is 12 watts pep , i have talked to people in Australia with less than that. Also a few shortwave receivers will let you enable the BFO on the AM BCB, one radio i had experience with was the DX-390 sold by Radio Shack but made by Sangean.
I have heard strange stuff on the AM BCB with the BFO kicked in.
EDIT: My mistake, 4 watts is not the power level for part 15 operations on 11 meters unless my math is wrong, (which is possible, i stink at math) Here is the correction according to the FCC.
TITLE 47 - TELECOMMUNICATION
CHAPTER I - FEDERAL COMMUNICATIONS COMMISSION
SUBCHAPTER A - GENERAL
PART 15 - RADIO FREQUENCY DEVICES
subpart c - INTENTIONAL RADIATORS
15.227 - Operation within the band 26.9627.28 MHz.
(a) The field strength of any emission within this band shall not exceed 10,000 microvolts/meter at 3 meters. The emission limit in this paragraph is based on measurement instrumentation employing an average detector. The provisions in 15.35 for limiting peak emissions apply.
(b) The field strength of any emissions which appear outside of this band shall not exceed the general radiated emission limits in 15.209.
And it would be easy to take measurements in this band since the equipment to do so is available.
Hi Guys and Neil:
I found a possible source for the balanced modulator
MC 1496 chip. The reason I say possible, is that
the company appears to have them on their
website, I just don't know about minimum orders
and that sort of thing. Will I have to buy a bunch
of them just to get one? I don't know.
So I'm going to try it. Again, I love to experiment,
so if this works, it works, if it doesn't, I'll just do
something else.
Best Wishes
Bruce, MICRO1690/1700
Mouser Electronics lists the 1496 at 92 cents. Minimum order 1. Plenty in stock.
Follow this LINK TO THE PART.
Hi guys:
I just realized that the MC 1496 chip can
be used as a balanced mixer, so it also
could be the basis for a transmit converter.
So here's my question. If I was to build
this circuit and inject the output of a
ham radio transceiver into one side of
the mixer and a local oscillator into the
other side, how would I protect the radio
and the transmit converter?
I have two low power transceivers that run
around 10 watts P.E.P out. One is on
ten meters and one is on forty meters.
Would I put a dummy load across the radio
and just take the RF from there on the hot
side (not ground?) Or would I have to
make some kind of splitter that put the
output into a dummy load but sampled
part of the output with resistors?
If anybody has any ideas, I would love to
hear them.
Bruce, MICRO 1690/1700
I really don't know enough about
this stuff, but the MC 1496
converter/balanced modulator
might need a power
amplifier to achieve the 4 or 5
milliwatts needed to transmit
SSB (or DSB) on 13.560 kHz.
It would be class A or B? Could
you do it with an MPF-102? Or
is that FET too low power for
that application? The reason I
ask is because MPF-102s are so
easy to get, and the circuits
for them look relatively simple.
Again, I'm really guessing on
this one.
Bruce, MICRO1690/1700
Thank you! I appreciate it.
(Regarding the availability
of the MC 1496 and the
link.)
Bruce, MICRO 1690/1700
part 15 on CB use to be 100mW DC input to final RF and a 60 inch antenna.
i guess now they go by f/s. wonder if they changed it for the very reason of people using it as an unlicensed b,cast station.
I bought a Radio Shack Space Patrol
Walkie Talkie in 1973 for the sole
purpose of being a one way communications
link between it and my Hammarlund
HQ-140X general coverage receiver on
channel 14, 27.125 MHz. The regen
receiver was useless but the transmitter
(100 mW input)
was quite useful. I still have the Space
Patrol Walkie Talkie and it still works.
Best Wishes
Bruce, MICRO1690/1700
It would be class A or B? Could
you do it with an MPF-102? Or
is that FET too low power for
that application?
When you see FETs used in RF power application they are usually in class C circuits where the FET is either full on or full off. This gives the legendary high efficiency of these amps.
I would not use a FET for a linear application (A or B) since they are inherently "square law" devices which means in their operating region they are not linear. The will amplify but they will also produce lots of unwanted extraneous signals which waste power and can cause interference. They can be used, but filtering and biasing get tricky. (FETS, especially the dual gate types, are very useful for mixing because of this non-linear characteristic.)
With the 1496 and considering the permitted FS levels you many not need amplification. The data sheet states that the maximum output voltage is +/- 8 volts p-p. That's not too puny but it is from a high impedance source (40 kOhm or so). If you use the 3.9 k resistors from Fig. 5 then the output Z is about 3.9 kOhms.
I noticed that there are two complementary output pins on this chip where one swings negative while the other swings positive. This would be perfect for driving a dipole except for the impedance mismatch. This modulator is essentially a switch which produces square waves at the carrier frequency rich in harmonics so filtering needs to be used.
Here's what I would try. Wind a step down transformer and connect the primary across the two outputs. Link couple a parallel resonant winding which connects to the antenna. Being resonant, it will suppress the harmonics. The turns ratio could be adjusted to get a good match to the antenna. The FS can be adjusted by how close the link is to the primary.
If the antenna Z were known then the ratio could be calculated. Otherwise, experimentation is needed. This is just an idea and I have not done this with this chip. I have done this with other transmitters with success so it may work with the 1496. Just something to think about.
Neil
Here's another way to approach this. I developed a circuit for my class lab which clearly demonstrates the DSB process as well as producing a very good signal. It worked well at BCB frequencies but I doubt the ICs I used would work at 13 mHz. The description below gives a good feel for the modulation process and is essentially how the 1496 works.
The basic idea is to multiply the audio signal by +1 or -1 at the carrier frequency. Since DSB modulation is just multiplication this will produce a DSB signal.
I used two unity gain inverting op amp circuits for the audio to produce two equal but opposite (180 degrees out of phase) signals, A+ and A-. To get DSB the circuit switches between A+ and A- at the carrier frequency. I used a 4016 quad analog switch ICs to do this. It was connected so one switch went to A+ and another to A-. A third switch was used to invert the carrier signal giving C+ and C- to feed the audio switch gates out of phase so in effect I had a SPDT (single pole double throw) analog switch operating at the carrier frequency. To get AM, all that is needed is to add DC to the audio signal (trivial since I was using op amps in the inverting mode) which unbalances the switching "bridge".
This scheme gives a lot of output power limited by what the audio ICs can handle since the 4016s are low ON resistance devices. Discreet FETS could be used instead if the gate biasing can be managed properly.
There is also a scheme called a "diode balanced mixer" which does the same thing using three transformers and four diodes. These are great for low level mixing and are available in IC packages. Due to stray capacitance effects and diode matching these are difficult to build and I wouldn't go this route for a hobby project. I just mention this in case someone wants to look them up to see how they work.
Have fun as you ponder these ideas.
Neil
Hi Neil. I knew you would have some good
information.
I do intend to pursue this. I have always
wanted to try to build these kinds of circuits.
I will take me a long time. In fact, I'm still
working on the 13 MHz AM transmitter.
I have learned more about electronics from
this board than anywhere else.
Thanks again
Bruce, MICRO1690/1700