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Sherlock Ohms

The Case of the Crazy Antenna

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WA4DOU
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Silver
Crazy Antenna
WA4DOU   1/11/2012 2:22:35 PM
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Very believable because it is so reflective of the everyday world we're all a part of anymore. Actually there are many communications technicians that don't have a full appreciation and understanding of antennas. Amateurs used to be the backbone of commercial radio because their motivation to learn went well beyond the limits of earning a living. Using "modern" testing methods, rote memorization can now earn an Extra class license, thus the loss of prestige that it once carried.

JimT@Future-Product-Innovations
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Blogger
Re: If only antenna couplings weren’t interchangeable
JimT@Future-Product-Innovations   10/12/2011 4:33:34 PM
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The proper antenna certainly would have been properly kitted at the time of sale.  Point being, however, that if a service call was made (after point-of-sale) that other similar looking, compatible-fitting, but actually WRONG antennas might have been pulled from the truck’s inventory, and installed on site. It sounds like that was the situation.

brett_cgb
User Rank
Iron
Re: The crazy antenna caper
brett_cgb   10/12/2011 12:26:21 PM
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As W.K. suggested, I believe the installers lacked the knowledge and/or equipment to properly test the antenna system (assuming they tested it at all).

On the story itself, you could have had an ideal feedline with a poorly matched antenna, and detected the Fwd/Rev power reported based only on where the wattmeter was inserted into the feedline.

A matched dummy load used during feedline testing would have been a more accurate test.

 

William K.
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Platinum
The crazy antenna caper
William K.   10/12/2011 11:34:24 AM
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Unfortunately upgrading an amateur radio license to extra is not enough. I have met at least one individual who passedd the test simply by going through the sample examinations a couple hundred times and memorizing all of the correct answers.

But understanding about feed line losses and antenna matching is "a very big deal" in the area of making a radio communication system work correctly. My guess is that the installers of the poor performance systems did not have the correct instruments, or did not use them, or perhaps did not understand the results. That does happen. And there are even some extra-class amateurs who claim that reflected power does not matter. So even that level of license is not a guarrantree of excellence.

hweidig3
User Rank
Iron
There ARE good small antenna companies
hweidig3   10/12/2011 10:04:33 AM
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It's always a good idea, but it's essential when you have a niche area, such as 900MHz trunked radio, that you clearly specify your technical requirements to your vendors. Otherwise, you can be taken for a ride (by accident or not) by suppliers who don't understand what you need. At JEM Engineering, we test test every single serialized antenna that we produce. We have near-field and far-field chambers, plus several analyzer types, to cover testing antennas from 30 MHZ to over 40 GHz. We even offer testing services to our competitors.

TJ McDermott
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Blogger
Re: If only antenna couplings weren’t interchangeable
TJ McDermott   10/12/2011 7:00:07 AM
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From the information provided, the antenna wasn't part of the turn-key package.  Was the antenna (and coax, for that matter) part numbers specified in the kit?

JimT@Future-Product-Innovations
User Rank
Blogger
If only antenna couplings weren’t interchangeable
JimT@Future-Product-Innovations   10/11/2011 5:38:56 PM
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I’m laughing with a wry smile – I spent over 20 years of my career in Motorola product development and have seen your experience played out more than once. The caliber of the typical “third-party” installation guys was hard to guarantee, but as you experienced; occasionally at the level of fresh-hires direct from the Dominoes Pizza delivery routes. Lacking a thorough understanding of a radiating system, to say the least. In Engineering, product design and antenna design always went hand-in-hand, and the antenna performance was always engineered to the Nth degree in the anechoic chambers.  But “fool-proofing” the antenna connection was not always done, and too often, the only guarantee that the proper antenna P/N was used would be the fine-print in the Field Service manual.  So many looked alike, it could have been easily overlooked; either accidentally, or intentionally, as you suggested.  But more likely, it was “accidentally” due to the limited technical skills of the installers.

vectorhappy
User Rank
Iron
CB shop work?
vectorhappy   10/11/2011 10:01:56 AM
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tell Paul to get his amateur license renewed and get that upgrade to Extra - wouldn't want the CB'ers to get the wrong idea. 

 

mikey

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