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Author Topic: 90 degree adapters lossy -- why?  (Read 1510 times)

Justin Goodman

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90 degree adapters lossy -- why?
« on: September 09, 2018, 09:09:50 pm »

https://www.rfvenue.com/blog/iem-ultimate-guide-redux

Reading this article, one quote in particular caught my eye. 2nd Question in the response from Brad (bolding mine):

"The second way to minimize loss is through less inline connections. Connecting straight from the  combiner to the antenna using one segment of cable is best. Adapting large 'N' type connectors to BNC is not ideal, and 90-degree type adapters are very bad for RF loss."

What about a 90 degree adapter is so bad for RF loss? Is he talking only about an adapter like this: https://www.parts-express.com/parts-express-bnc-right-angle-adapter-male-to-female--090-377 or also cable which is pre-made with a 90 degree connection like this: http://www.cablesondemand.com/product/CO-058BNCRBNC/URvars/Items/Library/InfoManage/CO-058BNCX200.htm

Either way, what's so bad about them vs a straight connector (like those you'd use in a panel patch bay, to front mount antennas in a rack, etc)?
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Henry Cohen

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Re: 90 degree adapters lossy -- why?
« Reply #1 on: September 09, 2018, 10:01:30 pm »

https://www.rfvenue.com/blog/iem-ultimate-guide-redux

Reading this article, one quote in particular caught my eye. 2nd Question in the response from Brad (bolding mine):

"The second way to minimize loss is through less inline connections. Connecting straight from the  combiner to the antenna using one segment of cable is best. Adapting large 'N' type connectors to BNC is not ideal, and 90-degree type adapters are very bad for RF loss."

What about a 90 degree adapter is so bad for RF loss? Is he talking only about an adapter like this: https://www.parts-express.com/parts-express-bnc-right-angle-adapter-male-to-female--090-377 or also cable which is pre-made with a 90 degree connection like this: http://www.cablesondemand.com/product/CO-058BNCRBNC/URvars/Items/Library/InfoManage/CO-058BNCX200.htm

Either way, what's so bad about them vs a straight connector (like those you'd use in a panel patch bay, to front mount antennas in a rack, etc)?

Right angle RF adapters are very easy to make incorrectly and thus introduce high insertion losses (>1dB). If it's designed and manufactured properly, it should introduce no more insertion loss than any other good quality adapter, about .5dB. The problem arises from most folk using Amazon or Parts Express as the sole source vendor for all things. There's a reason their stuff is cheap. Properly designed RF components are not inexpensive and the online  mass marketers are not the place to be shopping for them. Stay with good quality brand names:
Amphenol (and all their brand variants)
Pasternack
Radiall
RF Industries
Times Microwave
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Scott Holtzman

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Re: 90 degree adapters lossy -- why?
« Reply #2 on: September 10, 2018, 12:08:38 am »

Right angle RF adapters are very easy to make incorrectly and thus introduce high insertion losses (>1dB). If it's designed and manufactured properly, it should introduce no more insertion loss than any other good quality adapter, about .5dB. The problem arises from most folk using Amazon or Parts Express as the sole source vendor for all things. There's a reason their stuff is cheap. Properly designed RF components are not inexpensive and the online  mass marketers are not the place to be shopping for them. Stay with good quality brand names:
Amphenol (and all their brand variants)
Pasternack
Radiall
RF Industries
Times Microwave
You juat brought back memories of terminating right angle Phelps Dodge N-males on RG214.  The unbraiding, washers, the little screws that held on the center pin access plan.  Field termination was brutal.

The Crimp N connector is Nobel prize worthy.

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« Last Edit: September 10, 2018, 07:08:54 am by Scott Holtzman »
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Neil White

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Re: 90 degree adapters lossy -- why?
« Reply #3 on: September 10, 2018, 06:58:00 am »

The Crimp M connector is Nobel prize worthy.

Even better is the Times Microwave EZ connectors for LMR. The pin is pre assembled in the connector and locks into place on the cable with a nice positive click when the centre conductor is inserted. Then you just have to crimp the outer shield. Their stripping tool does the correct lengths for centre and outer in 2 steps, so no trimming or guess work required. We have had almost 0 failures with this across probably 100+  lengths of LMR400.
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Scott Helmke

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Re: 90 degree adapters lossy -- why?
« Reply #4 on: September 10, 2018, 10:17:59 am »

My rule of thumb about RF is that it "goes fast, doesn't like making sharp turns".  Good right angle adapters are expensive. Also you don't want to put sharp bends in your coax.
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Justin Goodman

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Re: 90 degree adapters lossy -- why?
« Reply #5 on: September 10, 2018, 01:44:18 pm »

My rule of thumb about RF is that it "goes fast, doesn't like making sharp turns".  Good right angle adapters are expensive. Also you don't want to put sharp bends in your coax.

Well... AC power and analog audio also "go fast," but right angle adapters are pretty normal in those contexts.  Really the issue/question was is there something specific to RF and 90 degree turns as the quote from the article seemed to indicate.

Henry's answer makes a lot of sense that manufacturing a quality one repeatably is more difficult than a $2 part allows for, and that a working professional who may show up to work on a tour but not necessarily own all the gear might have experience in the wild suggesting 90 degree adapters having a high susceptibility to failure/poor performance. 

I actually do need some 90 degree adapters (shallow rack) so it caught my eye. I've ordered the pre-built Amphenol cables at the appropriate lengths. 
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Scott Helmke

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Re: 90 degree adapters lossy -- why?
« Reply #6 on: September 10, 2018, 04:31:58 pm »

Well... AC power and analog audio also "go fast," but right angle adapters are pretty normal in those contexts.  Really the issue/question was is there something specific to RF and 90 degree turns as the quote from the article seemed to indicate.

RF moves quite a lot faster than analog audio, though.  It's where you have to start thinking in terms of it being a transmission line that can carry a train of waves, rather than something that's effectively always the same point in the wave over the whole length of the wire.
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Dave Garoutte

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Re: 90 degree adapters lossy -- why?
« Reply #7 on: September 10, 2018, 08:52:49 pm »

Technically, I think they both move at the speed of light through copper.
The RF just wiggles a lot faster.
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Scott Helmke

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Re: 90 degree adapters lossy -- why?
« Reply #8 on: September 10, 2018, 10:34:43 pm »

Technically, I think they both move at the speed of light through copper.
The RF just wiggles a lot faster.

It took me a while to really understand the difference between audio and RF.  RF moves *really* fast, basically like old cartoons where you'd see lumps of water moving through a hose. It's possible for there to be multiple waves moving through a cable of practical length. This is why you get reflections if the other end isn't properly terminated, because the waves have to go somewhere.

Audio on a wire, on the other hand, is like a solid rod inside a tube. If you wiggle one end of the rod, the other end wiggles right in time.  You could feel it if somebody held the other end steady instead of allowing it to wiggle. This is why you don't have to worry about termination and reflections on audio lines, unless they're really seriously long (miles).
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Lee Buckalew

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Re: 90 degree adapters lossy -- why?
« Reply #9 on: September 11, 2018, 04:15:54 pm »

Technically, I think they both move at the speed of light through copper.


Technically at about 70% the speed of light  ;)
That would be the propagation velocity. 

Lee
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