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Author Topic: Cushcraft "AFM" Series 4 Pole Arrays  (Read 1215 times)
KV4BL
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Posts: 74




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« on: June 11, 2002, 09:48:41 AM »

A few years ago, Cushcraft made three antennas that consisted of four 1/2 wave dipoles that were evenly spaced and could be varied for patterns from omni to directional and all points in between.  These seemed to be a viable alternative to the "Four Bay-Pole" designs by such companies as "Decibil Products" which routinely cost $800 or more per antenna, as the Cushcraft offerings were generally around or under $100 in price.  While the "Four Bay Pole" designs have definite advantages, I thought the Cushcraft offering looked neat but it was discontinured a few years ago for some reason that I did not understand.  Does anyone have any experience with the Cushcraft offerings (AFM-4DA in 2m, AFM-24DA in 220, and AFM-44DA for 440 MHz) and what was the performance and durability of these antennas like?  Also, a year or two ago while surfing, I found a ham radio store online (can't remember which one or where) that had a few of these still new, in the box and in stock.  Anyone know where I might still find one, especially the 2 meter AFM-4DA?  Thanks and 73,            Ray  KV4BL
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WB2WIK
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Posts: 20542




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« Reply #1 on: June 11, 2002, 11:28:52 AM »

Don't know who or where the ham store with old stock of AFM4D's is, although if you do a search on that model number, you might find them!

The Cushcraft 4-pole arrays were not nearly in the same league as the 4-poles from DB Products, Celwave (previously Phelps-Dodge) and other "commercial" houses.  I've installed a lot of all types, including the amateur Cushcraft models like the AFM4D, and the differences are drastic.

The downfall of the Cushcraft design is that each dipole uses a gamma match.  Thus, there are not one, but four gamma matches to adjust -- cumbersome at best.  But the worst part is that their gamma match design, the "Cushcraft Redi-Match" is not a good one.  It uses a polyester dielectric capacitor, and sliding, clamped aluminum-to-aluminum contacts between the gamma rod and the driven element.  This works just great for about five minutes, and then begins to oxidize and deteriorate.  No matter how tight you make the clamps, they begin loosening immediately by the standard cold-flow effect that impacts all things made of aluminum.  The contact resistance doesn't change to an open circuit, except in very extreme situations; however, milliohms of contact resistance -- too low to measure with an Ohmmeter -- dramatically impact the way this antenna works.  Of course, the fact that all bare (non-passivated) aluminum begins oxidizing the moment it is exposed to air doesn't help.

The commercial antennas (DB Products et al) use folded dipoles and all-welded (heliarc) construction, thus completely avoiding these problems.  The difference in cost, while large, is worth it.

WB2WIK/6
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KV4BL
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Posts: 74




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« Reply #2 on: June 12, 2002, 08:27:01 PM »

Thank You , Steve, for this informative and VERY helpful reply!  Now I have the "Paul Harvey" version on this antenna, thanks to you!  Also, I can stop wasting my time in a quest to find one of these recent relics.  Didn't know they were such a pain.  This fully explains their quick demise.  I figured they would not have the lightening protection of a DB or similar design as they are not the DC design of the comercial land mobile antennas, but I didn't realize just how far the advantages/disadvantages thing extended.  Again, thanks for the insight and info.         73,             Ray  KV4BL
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K9KJM
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Posts: 2416




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« Reply #3 on: June 13, 2002, 01:42:36 AM »

I agree with WB2WIK's comments on the Cushcraft 4 pole array completly. I had a set on a 200' tower a number of years ago that were just a pain. Hard to tune up, Very light duty construction, NO comparison to the commercial J pole arrays at all. If you are looking for an antenna that will be high up a tower for repeater or similar use, Go with the commercial variety. The last ones I have had experience with are
Sinclair, And they are Built! Along with most of the rest of the commercial variety.
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N6QDY
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Posts: 12




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« Reply #4 on: March 07, 2006, 10:44:58 AM »

(Three years later...)
Hello Folks, I was looking up the antenna, because I own one that I bought from Quement Electronics, before Quement Electronics closed the doors. Anyways, I bought it for $89 + tax back then. I remember putting it on the tower and taking it down right away, I thought it was my installation that caused this guy to run disfunctionally. Recently I ran across these antennas with the wiring harness and all (missing a U bolt and other hardware.) Anyways, I forgot all the heartache I went through and was considering putting this guy back up in a new repeater location. After reading your feedback I don't seem as thrilled about putting this antenna on the air now. I need to re-think and strategize.

On another note, if I decide to attach this dipole array to a tower, instead of attaching it to the tower directly I saw another alternative, I found another installation where a radio operator installed it to a long mast first, and then this person installed the mast to the side of the tower, I know this requires extra hardware, but it looked like a better install.. I was hoping you might comment on this.

Thanks again for your tips.

Regards,
     David N6QDY
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N6QDY
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Posts: 12




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« Reply #5 on: March 07, 2006, 10:45:48 AM »

My bad, I meant 4 years later... HI HI.
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