[Milsurplus] question - on BNC RF connectors

Sun Sep 1 11:17:49 EDT 2013

Well, I decided look it up. According to Amphenol, they ARE intermateable. So the OP should be ok. I would stick to amphenol to be sure.  But I also know that I have some off-brand versions that are not intermateable. I learned this the hard way by mating what I thought were two 50 ohm connectors. And when I tried to unmate them, the guts pulled out of one of them. Thinking this was a fluke, I tried about 20 of these that I got in a batch. All 20 were "hard to mate" and destructively unmated.  I contacted the seller of this batch and he indicated these were 75 ohm items not 50 ohm and so I made my conclusion.  BTW these were BNC to RCA adapters.

So I guess either I got a bad batch or some manufacturers do not adhere to Amphenol's strict specifications.

73 Eugene W2HX

-----Original Message-----
From: Mike Feher [mailto:n4fs at eozinc.com] 
Sent: Sunday, September 01, 2013 6:22 AM
To: W2HX; 'John Hutchins'
Cc: 'Milsurplus at mailman.qth.net'
Subject: RE: [Milsurplus] question - on BNC RF connectors

Gene -

I am not sure what you are trying to say here. If there is indeed a 75 ohm BNC, that I am still not convinced of, then the center contact both male and female would be smaller in diameter than the 50 ohm versions, providing everything else is identical. Just like in the N connector case, as the impedance is determined by the outside diameter of the center conductor and the inside diameter of the outer conductor along with the distance between them and the dielectric used. As I mentioned previously, at HF frequencies, and even low VHF, this is not even noticeable. 73 - Mike

Mike B. Feher, N4FS
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960 

-----Original Message-----
From: milsurplus-bounces at mailman.qth.net
[mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of W2HX
Sent: Saturday, August 31, 2013 6:57 PM
To: John Hutchins; Mike Feher
Cc: 'Milsurplus at mailman.qth.net'
Subject: Re: [Milsurplus] question - on BNC RF connectors

The other way will not work. Plus, because the female socket is a larger diameter than the 50 ohm male, you will not have a good connection. Expect diminished working frequency range.

73 Eugene W2HX

-----Original Message-----
From: milsurplus-bounces at mailman.qth.net
[mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of John Hutchins
Sent: Saturday, August 31, 2013 6:17 PM
To: Mike Feher
Cc: 'Milsurplus at mailman.qth.net'
Subject: Re: [Milsurplus] question - on BNC RF connectors

Group -

With the BNC connector Panel mount Female 75 Ohm will mate with a male
50 Ohm RG58C/U Pamona cable  just tried this out on my work table.
I am making up a few test fixtures, blocking capacitors, and such mounted in little metal boxes needed for the signal generator to meet various receiver alignment criteria.
Since we are talking about ~1/2" run length at most for the 75Ohm females connector.  I do not think that a 50 Ohm load requirement for the signal generator is going to suffer, that much of a miss-match.

Conclusion I have reached is that a 50 Ohm Male will mate with a 75 Ohm Female.

Thanks for you assistance.
Hutch

On 8/31/2013 9:22 AM, Mike Feher wrote:
> I am not sure about that. N connectors definitely have different 
> diameter male and female sections and are not interchangeable without 
> either damage, or, an open circuit. However, from what I recall, BNCs 
> are interchangeable as the only difference between the two is the 
> dielectric loading within the connector. At low frequencies, the only 
> problem if they do mate would be a
> 1.5 to 1 impedance mismatch jump, not a big deal for most applications.
> Regards - Mike
>
> Mike B. Feher, N4FS
> 89 Arnold Blvd.
> Howell, NJ, 07731
> 732-886-5960
>
>
> -----Original Message-----
> From: milsurplus-bounces at mailman.qth.net
> [mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of J. Forster
> Sent: Saturday, August 31, 2013 10:02 AM
> To: John Hutchins
> Cc: Milsurplus at mailman.qth.net
> Subject: Re: [Milsurplus] question - on BNC RF connectors
>
> The real 50 and 75 Ohm BNCs do NOT intermate w/o damage. The center 
> connector pin is different.
>
> You should use what the generator has.
>
> -John
>
> ================
>
>
>> Group -
>> Have generators that are 50ohm  and 75ohm outputs respectively. 
>> Making blocking capacitor modules; and RMA ant simulator module to be 
>> used between the two different generators.  Do I use 50 Ohm BNC or 75 
>> Ohm BNC connectors? Or does it really matter.
>> Thanks
>> Hutch
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