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 on: December 14, 2017, 08:38:25 pm 
Started by Al Rettich - Last post by Paul G. OBrien
You came unprepared,
Nonsense. I provided all 3 cable types that the projector supported.

 on: December 14, 2017, 08:17:21 pm 
Started by Debbie Dunkley - Last post by Henry Cohen
Impedance mismatches are to be avoided at (almost) any cost. Every time a impedance-mismatch occurs standing waves will occur, therefore degrading your signal. So: All cable, connectors and antenna either 50 ohm or 75 ohm.


This is a common misconception as it pertains to real world performance for low power wireless microphones, coms, IEMs and IFB's.

First of all, the mismatch between 50Ω and 75Ω is 1.5:1 - This is a return loss of 14dB, equivalent to a power loss of .177dB (96% transmitted power). This is better performance than the typical wideband antenna (LPDA, omni, circular polarized) sold for use with wireless mics, coms and IEMs, where a VSWR of 2.0:1 (return loss of -9.5) is considered good.
Here's the formula and online calculator.

Secondly, remember that an antenna is a transducer, which means it's actual impedance varies with frequency (just like a speaker). With wideband antennas marketed to cover in excess of 200MHz, their impedance will vary anywhere from about 37Ω to over 80Ω, being 50Ω roughly only in the center of the band.

Third, as it regards the front end of the wireless mic receiver, it too varies in impedance, somewhere between 50Ω & 75Ω with frequency due to parts choices and tolerances, and circuit design.

In the end, using 75Ω coax to the antenna will be no better or worse than using 50Ω coax. What will matter is the shield construction of the coax: A low loss braid over foil dual shield construction (e.g. LMR series, Belden 9913F7, PWS S9046), having 100% coverage, will exhibit far less attenuation and permeability to RFI than a single shield style such as standard RG58, RG8X. RG8, and RG213 having only 95% - 96% shield coverage.

There can be some merit however to matching impedance when connecting passives (splitter/combiners, filters, isolators, hybbrids, etc) together if they're being being used within their optimal performance range, but again, the mismatch loss is so small it's insignficant in RX applications and only marginally an issue in most TX situations. Now, if you're deploying a large distributed antenna system, with a lot of passive components throughout, the cumulative mismatches could add up enough to impact TX performance (but then your gain structure map would reveal that).

On the flip side, you can toss this entire commentary into the garbage if you're building commercial RF sites for land mobile radio, cellular/PCS/LTE/AWS, satellite earth stations (or the satellites), TV/radio transmission facilities, etc., where every .01dB matters.

 on: December 14, 2017, 07:47:57 pm 
Started by Kyle van dyk - Last post by Stephen Kirby
Intended usage is prime here.  Pointing to forums that talk about blowing up speakers would suggest hard usage such as small party DJ work.  Kyle, what are you going to use these for?  What kind of music, what kind of venues (size of room) and events (weddings or raves)?

 on: December 14, 2017, 07:43:22 pm 
Started by Al Rettich - Last post by Stephen Kirby
The most aware listeners I've encountered are women who have played an acoustic instrument at some point in their lives.  Especially if they've been in symphonic bands or orchestras.  They usually can't technically describe what they hear, but I usually get comments like "it sounds more 'real'".  They seem to focus on the overall sound.  Men have a tendency to pick the sound apart and focus on some aspect or other.

 on: December 14, 2017, 06:57:28 pm 
Started by Al Rettich - Last post by Al Rettich
I was able to guess the cymbals correct a few times.  We had to guess if it was in 48 or 96. 
Did you "guess" or did you pick?  Very different things.

Could you pick it out repeatably?

While there are differences in gear, the question "does it matter" much always come up.

Sometimes when listening to gear you can learn to hear the differences.

But that does not mean it is better, just different, and you have learned to recognize the differences.

But does that make it better?

 on: December 14, 2017, 06:06:10 pm 
Started by Bob Faulkner - Last post by Tim McCulloch
We have around 25 50a California or stove plug connectors down academy st now....

I got a lot of wire put in the ground when we renovated the street.

Glad everything survived the rain!

Sent from my iPhone using Tapatalk

Big fan of getting copper in the ground whenever you can.  Even an unfilled conduit if nothing else...

Eliminating trip hazards and providing permanent places power is available helps with future events and use planning.

 on: December 14, 2017, 06:04:27 pm 
Started by John Roberts {JR} - Last post by John Roberts {JR}
My house should be named "not to code".

Today I caught up with my local (real) electrician when he was across the street at the post office... He agrees we should probably put in a new 4 wire drop for the oven. He would like to put in a new panel too but agrees it is not an immediate problem.

I probably won't start shopping ovens seriously until after new years, and need to spec out the oven before specing the wire ampacity for the drop.

There are two 240V leads into the open junction box under the stove top so unclear what is coming/going exactly where.



 on: December 14, 2017, 05:55:50 pm 
Started by Mark Cadwallader - Last post by Tim McCulloch
All I was getting at was when your life can so easily be put in danger, what use is that "pretty good for 30 bucks" meter, when you can pony up some more for a meter that is trusted daily by so many working electricians.
Bunch of years ago, someone gave me a bargain basement DMM. Back at the shop, I put it through the Chop Saw, and tossed it. One of the Shop Lackies said he would have been happy to take it. I told him "I would never trust my life to it. Why would I want to give it to you?" I told him I'd go halvsies when he wanted a Fluke. Couple of months later, he got a REAL meter.

Steve, Chris, I'm pointing out that all we have is the manufacturer's *statement*.  That Fluke or Amprobe or Triplette or HP.... have track records of meeting their declarations and specs is a good thing and not one I'm dismissing.

And no, I don't own cheap knock-off meters... 8) 

 on: December 14, 2017, 05:54:20 pm 
Started by John Roberts {JR} - Last post by Tim McCulloch
You will note that my signature is "Not to code".

You, sir, are fast on the irony uptake. ;)

 on: December 14, 2017, 05:31:35 pm 
Started by Bob Faulkner - Last post by John Fruits
If you are price checking, Full Compass lists them.  Also worth checking with Mike Pyle for prices.

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