Some interesting articles have appeared in the February issues of QST. Here are three from the 1921, 1971, and 1996 issues…..Dan
Some Whys, and Speculation as to Some Possible Wherefores by M.B. West.
Some interesting speculation about how to improve the transmitters of the day. Remember, this was 100 years ago.
Quad vs Triband Yagi by Col. John Parrott, Jr., W4FRU.
Clarence Moore, the inventor of the cubical quad, probably little realized when he and his associates were huddled of the reference books back in 1942 that the product of their efforts would receive such widespread acclaim and damnation as has been poured out upon the cubical quad antenna.
The conclusion of the article, though, is:
One can expect to achieve the same or better results with a two-element quad of proper dimensions that with a three- or four-element triband Yagi.
A wide-space quad will perform substantially better that a close-spaced quad.
Dollar-for-dollar, the quad appears to be a better investment than a Yagi.
The question then, is, why are there still more Yagis than quads?
DSP—An Intuitive Approach by David Hershberger, W9GR
Digital signal processing (DSP) is, of course, all the rage now. Back in 1996, though, the technology was really just getting off the ground. Prices for DSP chis had dropped from around $200 to “$5 to $20” ($8.50 to $34.00 in 2021 dollars). W9GR writes, “This makes them ideal for low-cost amateur applications. Thanks to low-cost DSP chips, digital approaches….are now more than competitive with analog methods.” What follows is a nice explanation of basic DSP techniques, without a lot of math. Intuitive indeed.
Dave New, N8SBE says
Quads have been my favorite antennas since I first homebrewed a tri-band one with bamboo spreaders in high school. 50 years later, I still have the pieces/parts for that quad in my garage, with new, unused bamboo purchased almost 30 years ago from a local hardware store.
In the meantime, I lucked into getting a used Gem quad spider-boom tri-band antenna at a local swap. I re-strung it for individual feeds and six bands (20-17-15-12-10-6m) following the instructions found at https://www.qsl.net/ei7ba/Cubical%20Quad.htm
The article indicates that if you follow his loop dimensions, using uninsulated wire of the given gauge, that you will find that very little, if any, tuning will be required. Indeed, I found less than 1.7:1 SWR across the bands, except 6m, which I added myself, and apparently didn’t do a good job of calculating the wire lengths needed. I can still use 6m, though, with an antenna tuner at the radio end (yeah, I know, not very efficient, but it gets me on the band, and I can make contacts with it).
I also followed his strategy of using a mast-mounted antenna switch (his was homebrew, where I used an Ameritron 8-position remote switch, normally open contacts, and with lightning arrestors. I also followed his recommendations and wrapped a dozen turns of the feedline for each band through the appropriate toroid cores, to minimize common-mode currents, which had been an issue with my high-school homebrew quad.
It also turns out that with a 5-band quad, the loops are close enough to cause the impedance to be lower than the nominal 150 ohms for a full-wave loop, so you can dispense with the usual 75-ohm quarter wave coax sections to match the 150-ohm loops to 50-ohm coax.
Finally, I designed the feedlines from the remote switch to the driven loops to be a quarter-wavelength at each design frequency. This meant that when a given remote switch position was open (which is true for all but the one chosen for operation), the high impedance of the open relay at the remote switch end of the feedline is transformed into a virtual short at the antenna end. This effectively reduces the mutual coupling and RF feedback that would normally come down the unused feedlines. It works like a charm.
Unfortunately, I made a mistake, using RG-8X instead of RF-58 for the feedlines. RG-8x uses foam insulation, and if you exceed the minimum bend radius, which I most certainly did when wrapping them through the toroid cores, the center conductor will migrate through the foam and short or nearly short to the inside of the shield. DOH! RG-58 uses poly insulation, which is not as susceptible to migration.
The effect is after 10 years up in the air, some bands are shorted, and others arc over on voice or CW peaks. So, I’m going to have to pull the whole system down and re-do all the feedlines. I suppose after 10 years, it could use some TLC, anyway.
The nasty thing about spider-boom quads, though, is that you either need a tilt-over tower or a bucket truck to get them on and off the tower. I had a friendly tree guy with a bucket truck help me put it up, so I’ll been looking again to see if I can get my tree guy to help me with this.
Waiting for better weather to start this project. I’m still not interested in changing over to a Yagi, though. This quad has been a great performer on my 40 foot tower. I can break DX pileups with it, running barefoot 100 watts. Never owned an amp.