So after finishing up most of my projects a few days ago… I really needed something to do… so I put on the drawing board… a 100w automatic tuner that can work with the uBITx (intended to go inside the same case actually) that provides power, SWR, band memory for same antennas, low power tune, bypass, etc. all in a kit form for about $30. I’m prototyping the think now and will work on the tuning/communications code (to integrate into the Raduino) shortly. I’ve contacted a few of you off-channel to work out some protocol/communication issues… but Stay tuned (double play on words there)!
Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ
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Villa Grand Piton – J68HZ
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So the ALE (automatic link establishment) crowd, much like the WINLINK crowd, tend to use LOTS of bands....and thus they find ways to make their antenna systems work on mulltiple bands. Here are some of the most popular ways:
1. Fan Dipoles (time honored technique of tying multiple dipoles together at the CENTER, and the energy tends to go to the correct one, since all the others present much higher impedances. The wires "fan" out with usually wooden spreaders at the end and some string involved to keep them somewhat separate. Been there done that many times, my college ham club has a 3-band unit up on the top of an 11 story building rightnow that I built for them. Build for yourself, dirt cheap.
2. Auto-tuners --- everyone makes these now and many can tune as soon as they see RF, or even return to previous settings that were memorized. LDG, and others. Low power versions for $100 End fed wire to balanced line fed dipoles---they work with lots of different kinds of wire.
3. Inherently multiband antennas: example, full wavelength loops. Build for yourself.
4. Carefully tuned end-fed transformer-fed antennas --- there are now several of these on the market and they give an acceptable SWR on mulltiple harmonically related bands. Tend to be close to $100
5. (the one I dislike) resistively terminated folded dipoles --- these use a resistor to make up for what a folded dipole can't create and give an SWR that is "acceptable" literally across EVERY FREQUENCY in a decade of frequencies. 3-30 MHz. The tradeoff is loss, as much as 10 db at times. And they generally are pricey.
6. There are some multi-band vertical antennas on the market that are basically vertical fan dipoles, but scrunched up in a nice package. An elderly ham in my city has one, 32 feet tall....a gang of us put it up and doggone it does from from 40 meters all the way through 6 meters
And there are probably many more....
An automatic tuner protects the rig during TX. If the SWR is bad during TX, some of the signal coming out of the transmitter is reflected by the antenna back into the radio where it can cause damage.
That said, RX is optimized by a properly tuned antenna, but some good amount of signal still makes into the radio when receiving, even when the antenna is not perfect.
So I assume Doc G² is scanning for radio traffic, and then when he finds some if he wants to transmit he does something about his SWR for that frequency.