Hello Good to be Home!
Check out the clever square loop made from copper pipes by scrolling down this link page to the “Unfair Transmitter.”
Hello Good to be Home!
Check out the clever square loop made from copper pipes by scrolling down this link page to the “Unfair Transmitter.”
http://www.techlib.com/electronics/amxmit.htm
For that matter the whole page is interesting.
Glad everybody’s back!
Wow! Major Techlib update!
Mr. Wenzel has been busy. Techlib.com has always been a favorite of mine but I obviously haven’t been by there in quite some time.
Awesome!
Wenzel update
I also had not seen the new Wenzel loop antenna design. It’s interesting, but I wouldn’t build it myself, largely because Wenzel’s transmitter design philosophy does not include any interest in high efficiency. If there is ever a need for a high-efficiency transmitter design, it is in Part 15 AM.
I built Wenzel’s “improved circuit” a few years ago, but I used a higher Q core for the output transformer. The recommended potcore has very low Q, although Wenzel says that it is high Q. With my improved transformer core, I got only about 16% efficiency. Wenzel’s original circuit would have given significantly less than 10% efficiency. Wenzel’s circuit has a transconductance modulator, which is very similar to the SSTRAN circuit. Replacing the output transformer with a capacitor input “L” network, like in the SSTAN, brought the efficiency percentage up into the 20s, which is still not very good. I will say that the modulation linearity with the transconductance modulator is very good. This must be why the SSTRAN has a reputation for very low audio distortion.
Here is how I modified the circuit to get higher efficiency: I used the left-hand emitter follower transistor, and the transistor at its emitter, as a high-outout emitter follower that buffers the oscillator. I rewired the right-hand emitter follower transistor as a grounded-emitter class-C amplifier stage. I drove the class-C transistor stage with the buffered oscillator output. Operating the output stage in the class-C mode increased the efficiency to more than 50%. My modifications disabled the transconductance modulator, and I used a transformer-coupled collector modulator instead.
I gave only an outline of my modifications, and not the details. Please don’t attempt the modifications unless you understand electronic circuits.
Antenna performance
I should point out that in my previous post, I was comparing the transmitter output with a high-Q output transformer with the transmitter output with an impedance matching network, but no loading coil. The secondary winding of the output transformer acts like a loading coil. The true comparison with an antenna connected to the transmiter output depend upon how the Q of the loading coil compares to the Q of the output transformer.
Square Loop…Directional?
Just a note about the very interesting Loop Antenna design in the article. The major advantage I can see to this design is that it is slightly directional off of either face of the loop. Because the loop is very small in relationship to a full wave length at operational frequency, the signal would be very nearly omni-directional. The signal off the ends of the loop would “squashed in” very slightly. Adding “passive” loops at some distance from the radiating loop has the potential to add directionality to the array. the size and spacing of the passive loop would act very similar to the Yagi-Uda design used in amateur radio. Just some stuff to roll around in the brain cavity.