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Author Topic: Using BNC connectors instead of UHF connectors for antenna hookup?  (Read 7275 times)
N3KXZ
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Posts: 77




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« Reply #15 on: January 07, 2014, 11:24:46 AM »


I'd ditch the Daiwa idea.  There's military surplus stuff that's much higher quality and a better deal overall.
Dow-Key (commercial) 3-position BNC here for $35: http://www.surplussales.com/switches/SWcoaxial.html

That's just one example.  There are hundreds of them out there at the surplus houses.

Thanks- just the kind of thing I was looking for! I've never seen them before. Were they intended for panel mounting? I don't see a flange on any of the photos.

Keith
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K2GWK
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« Reply #16 on: January 09, 2014, 07:35:50 AM »

I seem to remember that you can get 'away' with 50 and 75 ohm BNC but not type N - I can't remember why the BNC was different.

When you look at the skin depth when you go to 432MHz, there is an advantage in larger diameter pins, as it lowers the current density when running QRO. Type C is better than Type N. Still, many people have successfully used 500 or 1000 watts at 432 through Type Ns.

The center pin on a 50 ohm type "N" connector is physically larger than the 75 ohm version. Trying to mate a 50 ohm male N connector with a female 75 ohm N connector will result in the destruction of the 75 ohm connector's center pin. Mating a 75 ohm male type N connector to a female 50 ohm type N connector will result in poor contact of the center pins due to the center pin size difference.
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K2GWK Website

Stupidity for Dummies (http://stupidityfordummies.com/)

…because sometimes, you just can’t dumb it down enough…
WA3SKN
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« Reply #17 on: January 10, 2014, 07:32:03 AM »

BNC connectors are good up to about 1200 MHz, and are weatherproof (rubber gasket inside)... which will deteriorate after about 12-15 years, not usually a problem.  They are not really for high power applications (KW+).
You do need to know about the 50 vs 75 ohm pin sizes though.  If they get intermixed it can cause opens that are hard to trouble shoot. Cost used to be a factor.
73s.

-Mike.
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N3DT
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« Reply #18 on: January 10, 2014, 05:45:14 PM »

The 50 ohm and 75 ohm BNC connectors have different size center pins.  Best not to mix them or you'll find they get intermittent.
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AD5X
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« Reply #19 on: January 11, 2014, 05:28:31 AM »

The 50 ohm and 75 ohm BNC connectors have different size center pins.  Best not to mix them or you'll find they get intermittent.

The center pins are the same size, so they can be intermixed.  But there will be an impedance bump which may be an issue at higher frequencies.  But probably not as much of an impedance bump as you see with UHF connectors!

Phil - AD5X
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WS4E
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« Reply #20 on: January 11, 2014, 06:27:45 PM »

I went all BNC in the shack because I wanted to get RID of switches.   With multiple rigs(3 HF, 2 VHF, and 2 SDR) and multiple antennas(8 total HF+VHF), it's seems like 10000X better to use a 32port BNC patch panel and effortlessly be able to patch any radio to any antenna, or to a dummy load, or insert an analyzer or wattmeter  in the line or anything else. I have all outputs(antennas) on the top row, and all inputs(rigs on the bottom).   A bottom always has to be connected to a top, never a bottom to bottom or top to top.  Keep that straight and should not do anything dumb.  I used LMR240 for all the cables I to make where I could not connect an existing run directly in like those from a couple of attic antennas that were already run to that point.  

I got a surplus BNC patch panel for $30 off eBay(I saw bunches of them on there) and will sell several $60 antenna switches and be happier and pocket the difference.  And I ordered a 19" 1U swing out wall  mount to attach to the wall, which was another $20 off some website the net.  

Here is a pic.  I just started hooking it up over new year weekend.  
http://imgur.com/bYRQgAJ

Just got the antennas run so far (up the left) plan on running the rigs this weekend(right side).  

You might want to think about this setup.  It's quite functional compare to the kind of antenna switches I used before (alpha delta) and much cheaper once you add them all up.  

Only negative is...of course you know I am going to have to get more radios and antennas to fill all those ports.  Smiley
« Last Edit: January 11, 2014, 06:36:29 PM by WS4E » Logged
N3KXZ
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« Reply #21 on: January 11, 2014, 06:43:56 PM »

That seems like a great idea. But 'm surprised those BNC patch panels can handle much power. What are they rated for and how much power are you putting through them?

Can you identify that patch panel- model number etc?

Thanks,
Keith
N3KXZ
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WS4E
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« Reply #22 on: January 11, 2014, 07:39:46 PM »

That seems like a great idea. But 'm surprised those BNC patch panels can handle much power. What are they rated for and how much power are you putting through them?

Can you identify that patch panel- model number etc?

Thanks,
Keith
N3KXZ


I don't see that they would be any different than regular BNC power.  The construction is simply a flat piece of steel, with 32 holes drilled in it and 32 F-F bulkhead connectors screwed into the holes.  Basically you have a BNC coupler in line, and that is about all there is to it.


From what I have always heard, BNC is good to a KW or more, but usually the main limiting factor on whatever connector your using BNC/TypeN/PL/or whatever is really whatever the cable will handle.  And RG8/RG8X is much more limited in power capability than the connectors are.

Also remember the BNC is dimensionally almost exactly the same as a Type-N connector(even have exact center pins) so far as the areas that carry all the current and voltage, so it is good to a kilowatt or more(legal limit).

Hence, I would guess the BNC (same conductors and size) will be similar capable, since the only thing different in the connectors is in the ground/shell one is threaded the other is twist on.

Frankly I am one of those guys who can't understand why hams don't stop using the old hard to install correctly PL connector and use something better (BNC,N,TNC).....and don't get me started on why hams don't move to using 75Ohm when most cable TV RG6 has better shielding than LMR400.


« Last Edit: January 11, 2014, 07:51:59 PM by WS4E » Logged
WB6BYU
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« Reply #23 on: January 11, 2014, 08:34:47 PM »

Quote from: WS4E

...A bottom always has to be connected to a top, never a bottom to bottom or top to top...



And if you were worried about possibly making a mistake, use type N connectors on one set
and BNC on the other, with one of each on all the patch cords.  While that doesn't prevent you
from making mistakes (you could still connect two rigs together through an SWR meter, for
example) at least it requires more work to get it wrong!
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N3DT
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Posts: 516




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« Reply #24 on: January 12, 2014, 04:13:48 PM »

There may be some 50Ω BNC connectors that are the same pin size as the 75Ω ones, but most audio guys say not to mix the two because the 50Ω usually have a smaller pin and when you connect a 50Ω male to a 75Ω female you can get intermittent connections.  I've had it happen.

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W0BTU
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« Reply #25 on: January 12, 2014, 04:37:42 PM »

From what I have always heard, BNC is good to a KW or more, but usually the main limiting factor on whatever connector your using BNC/TypeN/PL/or whatever is really whatever the cable will handle.  And RG8/RG8X is much more limited in power capability than the connectors are.

Also remember the BNC is dimensionally almost exactly the same as a Type-N connector(even have exact center pins) so far as the areas that carry all the current and voltage, so it is good to a kilowatt or more(legal limit).

Hence, I would guess the BNC (same conductors and size) will be similar capable, since the only thing different in the connectors is in the ground/shell one is threaded the other is twist on.

Exactly right.

I know more than one ham who runs the legal limit through BNC connectors. Don't remember what coax they used, but it was likely that small PTFE stuff that will handle 9 kW. For 160 (and maybe 80) RG-58 or RG-59 would probably not get very warm at 1500w.

Quote
Frankly I am one of those guys who can't understand why hams don't stop using the old hard to install correctly PL connector and use something better (BNC,N,TNC).....and don't get me started on why hams don't move to using 75Ohm when most cable TV RG6 has better shielding than LMR400.

I agree. Maybe one the reason is all the coax ads. Nobody buys paid ads for inexpensive RG-6. :-)

All the outdoor coax at this QTH uses flooded quad-aluminum-shield F-6 (RG-6). And the F-6 to the 160 meter inverted-L uses F connectors--and they have not failed yet even at the legal limit. Neither the coax nor the F connectors even get warm.

If F connectors can handle 1500 watts during multiple CW contests, a BNC certainly can.
« Last Edit: January 12, 2014, 04:42:15 PM by W0BTU » Logged

N3DT
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« Reply #26 on: January 12, 2014, 05:25:52 PM »

I'll have to agree with the RG-6 thing.  You can get 200' of the quad shield stuff for about $30 delivered on the e place, with the F connectors installed and the stuff has incredible lack of loss.  I measured about 8 dB for the 200' at 1GHz.  You can just forget the 50/75 ohm difference, your antenna probably isn't that close anyhow. I got a Nortel GPSTM and it recommended the RG-6 and F connectors.  Of course there's no transmitting going on there, but I wouldn't hesitate to use the RG-6 for any of my HF antennas.  Wish I'd discovered it earlier.  Probably nothing wrong with F connectors if you make a clean install and use de-ox or even the teflon goop, wrapped of course.
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W0BTU
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« Reply #27 on: January 12, 2014, 08:42:03 PM »

RG-6 will handle 1500 watts continuously up to about 10 MHz, and intermittently (typical ham use) to 28 MHz.

On 160, it will handle almost 3 kW continuously.

And its loss curve from 1 to 100 MHz is almost identical to that of RG-213.

The only thing I've ever put inside connectors is silicone dielectric compound. All my F connectors that handle power have that applied, indoors or out.

I also remove the sharp edges all the way around the center conductor with a small, fine file. If you don't, you risk damaging the plating on the female contacts.
« Last Edit: January 12, 2014, 08:55:44 PM by W0BTU » Logged

G3RZP
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« Reply #28 on: January 13, 2014, 01:48:15 AM »

It's interesting to figure the skin depth at 432 and the resulting current density at the surface of an N connector pin at 1500 watts. Rather frightening, too.....
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