The Shrunken Quad is a design described in TRANSMITTER HUNTING - Radio Direction Finding Simplified, and is popular as a sniffing antenna with many hunters. Here are some postings to the Foxlist about this antenna.
From: Jim_Bowman@ATK.COM (Jim Bowman) To: fox-list@netcom.com (FOX-LIST) Organization: Alliant TechSystems, Inc. Date: Thu, 14 Mar 1996 13:50:06 GMT Subject: SHRUNKEN QUAD Sender: owner-fox-list@netcom.com Greetings to the list I am interested in any advice/feedback from the list regarding the "Shrunken Quad" described in the book "Transmitter Hunting - Radio Direction Finding Simplified" by Joe Moell, K0OV. I built one, but have not found a source for the piston trimmers in the necessary value. I tried some small air variables, but had no luck getting any indication of proper tuning using my MFJ antenna analyzer. I also tried some small compression trimmers I had in the junk box, although I can't be certain of their value. I tried resonating the driven element alone, to try to minimize any possible effects by the second element. No luck. I also wonder if anyone has tried any alternative to the coaxial balun as described in the book. I wonder if a few ferrite beads or a coil of a few turns of the coax at the antenna feed point would adequately isolate the coax, or ?? In other words, I'm wondering if my coax balun is a problem. I even tried to couple directly to the loop to see if I could resonate. The capacitors across the loops are such a small value, I wonder if it would work to just use insulated wires twisted together in place of the capacitors, and snip the twisted pair back a little at a time to adjust the capacitance? I think this is a nifty little quad, and would like to get it working properly. Any help would be appreciated. 73, Jim W7HPK jbowman@ATK.COM ------------------------------------------------------------------------ From: Bruce Paterson Subject: SHRUNKEN QUAD (fwd) To: sleipnir!fox-list%netcom.com@sleipnir.iaccess.com.au (Foxhunt Mailing List) Date: Mon, 18 Mar 96 20:30:22 EDT Mailer: Elm [revision: 70.85] Sender: owner-fox-list@netcom.com *Greetings to the list * *I am interested in any advice/feedback from the list regarding the "Shrunken *Quad" described in the book "Transmitter Hunting - Radio Direction Finding *Simplified" by Joe Moell, K0OV. I built one, but have not found a source for *the piston trimmers in the necessary value. I tried some small air *variables, but had no luck getting any indication of proper tuning using my *MFJ antenna analyzer. I also tried some small compression trimmers I had in *the junk box, although I can't be certain of their value. I tried resonating *the driven element alone, to try to minimize any possible effects by the *second element. No luck. I've built a 6m version (just everything scaled up to 52MHz) and boy is it touchy ! The capacitors _do_ need to be good quality, and their adjustment is critical to get a good F/B ratio. The chair spring two element 6m yagis I built previously _seem_ to be less critical in their adjustment (even though they don't look nearly as pretty in their construction). The Quad didn't end up working on a hunt, probably 'cause something critical got bumped. I'll give it another go sometime, but given my experience so far I'm not sure if I'd recommend them yet..... * *I also wonder if anyone has tried any alternative to the coaxial balun as *described in the book. I wonder if a few ferrite beads or a coil of a few *turns of the coax at the antenna feed point would adequately isolate the *coax, or ?? In other words, I'm wondering if my coax balun is a problem. I *even tried to couple directly to the loop to see if I could resonate. I used a normal gamma match onto the quad driven element. That part works fine ! There is no reason gamma & delta matches can't be used on Quads as well as Yagi. For some reason not many people seem to. *The capacitors across the loops are such a small value, I wonder if it would *work to just use insulated wires twisted together in place of the *capacitors, and snip the twisted pair back a little at a time to adjust the *capacitance? Better use pretty thick un-bumpable wires... *I think this is a nifty little quad, and would like to get it working *properly. Any help would be appreciated. Sorry I can't help more. How about someone replying who has been repeatably successful ? ------------------------------------------------------------------------ From: lra@top.monad.net Date: Thu, 21 Mar 1996 10:45:29 -0500 To: fox-list@netcom.com Subject: Shrunken Quad Experiences Sender: owner-fox-list@netcom.com For what it's worth, I built a shrunken quad a year or two ago and had a terrible time with it. Wound up giving it away at a hamfest! However, I will admit the following: 1. I didn't use piston caps, rather a compression trimmer of some sort, perhaps not even exactly the right range. 2. I used a fairly thin gage wire. I couldn't get the thing to resonate, or to act even remotely directional. In any event, I thought the design was pretty cool, and think it would be an ideal antenna - if I could make it work! Since then I noticed that hamtronics has 1-10 pf piston caps listed in their catalog, but haven't tried any yet. I have built a 440 MHz quad for third harmonic hunting, but haven't given that a field test yet. I think that might be a good compromise antenna - usable on 146 or 440, and fairly small. Anyway, while I can't lend any good advice on the Shrunken Quad, count me as one of the group who would sure like to get one to work! 73, Larry Antonuk WB9RRT/1 Keene, NH ------------------------------------------------------------------------ Date: 27 Mar 96 23:31:50 EST From: Joe Moell To: Fox-list Subject: Help for the Shrunken Quad Sender: owner-fox-list@netcom.com I sent Shrunken Quad info directly to Jim, but some of it may also be of interest to the list. This antenna DOES work very well, provided you build/tune it correctly and don't expect to use it over a wide frequency range. I have rebuilt my original 2m Shrunken quad using 1/4" diameter fiberglass spreaders and 3/32-inch bronze welding rod elements. It is now extremely rugged, and has withstood lots of tramping in the brush. I also built a 6 meter version that I use regularly on the van for the monthly 6m hunt in southern California. Not just any old piston trimmers will do. The easiest ones for hams to find are the kind that look like a ceramic tube about 3/4 inch long with plating on outside and a screw with rather coarse thread that goes in and out. THESE DON'T WORK, because the adjustment is too coarse for this high Q circuit. The ones I recommend are 1/4 inch in diameter and 1/2 inch long, completely enclosed in ceramic and brass. They have a constant-torque drive with very fine thread. It takes 11 turns of the tuning tool to cover the the full capacitance range. The piston and bellows are internal and the whole thing is sealed, so moisture/water won't upset the tuning. They are similar to Johanson 5201PC series in the Newark catalog. For a less expensive source, try Bogdan Electronic Research & Development (Jim & Carolyn Bogdan), PO Box 62, Lakewood, CA 90712, 310/634-0911. They have had these trimmers for sale at swap meets and the VHF conferences. It takes some painstaking tuning back and forth on the capacitor to get the driven element and reflector to resonate properly, so twisted wires aren't practical. Besides, you would have to find some way to encapsulate them or they would get detuned from handling in the field. The balun on the Shrunken Quad is of the "bazooka" or "sleeve" type, which consists of an extra length of braid, an electrical quarter wavelength long, placed over the antenna end of the RG-58 coax feedline. The sleeve is connected to the RG-58 shield only at the end closest to the receiver input. The antenna end of the sleeve is left open. Special coax is not required. For more information on sleeve baluns, see the "Linear Baluns" section in the "Transmission Lines" chapter of a recent ARRL Handbook. Instructions for making the balun: Make a quarter-inch cut in the feedline jacket 12.9 inches from the antenna end, exposing the braid there. (Don't remove the entire foot of jacket---just a little quarter-inch ring of it.) Now take some braid from old coax, smooth it down over the outside jacket on that last 12.9 inches, and connect it to the shield at the point where you cut the jacket. Leave the other end open. Put tape or shrink sleeving over the added braid to prevent shorts. Joe Moell K0OV Homingin@aol.com