So here¡¯s an oddball connector usage from the opposite end of the spectrum - a perfectly good HP 355C VHF attenuator (BNC connectors) has been bastardised and is ?being used as a 600 ohm 1dB step attenuator with a maximum attenuation of 12dB¡ It¡¯s currently on the local internet auction site and the seller ONLY ?wants $NZ500 ($US250ish) for it! DaveB, NZ ? ?
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From: [email protected] [mailto:[email protected]] On Behalf Of Tom Lee
Sent: Sunday, June 30, 2024 06:54
To: [email protected]
Subject: Re: [HP-Agilent-Keysight-equipment] BNC Frequency Limit? The word "limit" should not be interpreted as a fixed, discrete boundary that separates "useful" from "useless". The world is analog, so it's best to consider what is really meant in a given circumstance.
For a frequency counter to function properly, all you need is to preserve the zero crossings and some minimum amplitude, so that's a fairly forgiving application. That said, I am surprised to hear that your counter's 22GHz input uses a BNC. High-frequency counters often have a couple of connectors, one covering up to a couple of GHz and another above, but I've never seen or heard of a BNC being used in a commercial instrument for 22GHz -- could you let us know the instrument model? Or is it a homebrew counter?
That aside, in other situations you might need to worry about impedance mismatch. And that's where a typical BNC connector has unfavorable characteristics as you increase frequency. The instability of the ground connection is also a problem (particularly in mobile applications, where the modulation of impedance can cause the BNC to act as a surprisingly good vibration sensor). BNCs are also manufactured to fairly loose tolerances, so if the application demands accuracy and precision over a wide frequency range, BNCs aren't going to be a good choice.
So, it's not as if signals abruptly stop emerging from the BNC once you go above, say, 4GHz. It's more complicated than that. And whether a BNC is useful or not in a given circumstance depends very much on what performance you need in that particular case. The frequency "limit" will vary accordingly.
-- Cheers
Tom
-- Prof. Thomas H. Lee Allen Ctr., Rm. 205 420 Via Palou Mall Stanford University Stanford, CA 94305-4070 On 6/29/2024 10:58 AM, Jinxie via groups.io wrote: Hi all,
According to this site:
50 ohm BNC connectors are only good up to 4GHz and 75 ohm ones to 2GHz maximum. And yet - to take just one example - my best frequency counter, which accepts and can measure signals up to 22Ghz, uses 50 Ohm BNC sockets and seemingly works just fine with them. And yet it's not just the Historytools website which claims BNC is only good up to a few GHz; plenty of other sources say the same thing. What's going on here?
Thanks,
J.
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...And dont?forget Wangnet which uses a BNC alongside TNC in its contra-rotating ring topology.
Pete
On Sat, Jun 29, 2024 at 10:15?PM Chuck Harris via <cfharris= [email protected]> wrote: Probably only about 6 gadzillion were used on routers before
the inverse SMA became popular... But, no, they didn't catch
on in the test equipment world.
-Chuck Harris
On Sat, 29 Jun 2024 13:32:04 -0700 "Jinxie via "
<paul666=[email protected]> wrote:
> TNC are several orders of magnitude better than BNC IIRC. Far more
> phase stable (that's another aspect we haven't mentioned yet). Shame
> they never really caught on; bit like Betamax and VHS. :(
>
>
>
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Hi Jim,
I could be wrong but I'm not sure this is totally accurate....
"Regarding TNC connectors, they are common for military applications where you just can't rely on the bayonet mechanical connection of a BNC.? You don't want your connectors vibrating loose on your aircraft, after all. "
The last thing I'd want is for vibes to loosen a threaded connector, which can happen.? I had my head inside a B757 E-E bay a few years ago doing some experimentation and I had to contend with getting a "Type C" adapter so that I could connect into the antenna interface of a VHF comm radio.? Type-C is a bayoneted Type-N connector.
73.....Frank / WA3NHK
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A very interesting discussion. Who really knows how that S-D counter with MW input came to have a BNC!? Maybe a "factory special" made for some very particular user! (you can buy anything you want if you have the $$) Very, very odd. I agree with Chuck H. as I, as well, have had tons of SD counters starting with their knock-off of the HP5245 called the 1037, and going up into the 6245 and above series (I may still have some around somewhere). Never saw a BNC used in a test equipment design for over a few GHz (although, as pointed out, will probably work, even if lossy!)
Now, on to TNC: A threaded BNC type, used initially to 12 GHz then improved to 18 GHz, popular in avionics like the APR-25 radar warning receiver used extensively in 'Nam. It is more rugged than an SMA (and I would argue,easier to connect/disconnect inside a tight fighter jet A/C equipment bay without damage), smaller/lighter than a N, manufacture is relatively cheap, and so on. A BIG user was NASA, and particularly JPL on the DSN because of the low RF leakage spec provided by the threaded portion. Even though the innards are the same as a BNC, the bayonet shell of a BNC leaked enough to bother the folks dealing with the deep space stuff! I saw racks of 100 MHz frequency distribution stuff at Goldstone -Current stuff! All plumbed in TNC. A great connector for certain uses and definitely can be had cheaply! People have given me good stuff for Gratis that was TNC based.
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Also, the E4440A PSA spectrum analyser operates to 26.5 GHz and it uses a special version of the N connector.
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You'll find type N on an 8566 spectrum analyzer to 22 GHz.? I'd expect the spec an to be more demanding than the frequency counter.? My 5343A counter goes to 26.5 GHz and has a male APC 3.5 mm connector on it, while my 8566A spec an goes to 22 GHz and has a type N on it.
Regarding TNC connectors, they are common for military applications where you just can't rely on the bayonet mechanical connection of a BNC.? You don't want your connectors vibrating loose on your aircraft, after all.? Bonus that they support higher frequencies than BNC.? I've seen TNCs on handheld military radios, where a type N would be too bulky.
SMA was developed to be an inexpensive and compact way to connect to 18 GHz, since pushed in some cases to 26.5 GHz.? Amphenol and HP came up with the APC 3.5 mm connector for use in testing devices with SMAs on them and for use up to 26.5 GHz.? Wiltron, now part of Anritsu, one-upped HP with the 40 GHz 2.92 mm "K" connector.? 3.5 mm and 2.92 mm connectors are mechanically compatible with SMA.
HP was not about to buy connectors from a competitor and made their own 50 GHz 2.4 mm connector but made it incompatible with the SMA types.? Wiltron, IIRC, one-upped HP again with the 60+ GHz 1.85 mm "V" connector, which I believe is mechanically compatible with the 2.4 mm.? Then Southwest Microwave came out with the (very expensive) 1.0 mm connector for up to 110 GHz.? Since then, several German companies, I think Rosenberger and Spinner among them, came out with the 86 GHz 1.35 mm.? One would guess the idea was to handle E band, 71-86 GHz (with a hole in middle from 76 to 81 GHz) at a lower price point than the ~$1000 1.0 mm connector.? I've also heard rumors of 0.9 mm and 0.8 mm connectors to get up aroun 200 GHz(!)? I can only guess how much those would cost....
HTH
Jim Ford Laguna Hills, California, USA
On Saturday, June 29, 2024 at 04:43:50 PM CDT, Greg Muir via groups.io <big_sky_explorer@...> wrote:
Systron-Donner 6054B ¨C the 20 MHz -24 GHZ connector on stock models certainly looks like an SMA to me.? The 20 Hz -20 MHZ input is a BNC.? The S-D catalog calls out (verbatim) ¡°SMA-3MM. Other input connectors available on special order.¡±
A BNC modification would nicely fit into the hole made for a SMA if a slight modification to the hole were made with no trace of any hacking.
Greg
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I suppose lots of things could have happened. It 'might' have had the BNC fitted from new as a factory option, but then again, it could be that the original SMA got damaged and the only bulkhead connector available for a quick repair was a BNC type.
Either way, I'd expect it to work quite well as a frequency counter up to 18GHz with a fairly decent BNC connector at the input. Above this, the input impedance could become quite different to 50R. As it is just a counter, this probably doesn't matter much so it will probably still function OK to 20GHz. I'd expect to see some issues above 20GHz but it might still function OK as a counter if driven with a level > -20dBm?
By 24GHz there might be some dips in the response especially if it is fed from a source that doesn't have a well defined 50R source impedance above 18GHz. There could be some big (source to load mismatch) dips in the frequency response because of this. In other words, it might work OK to beyond 20GHz when tested with decent 50R test gear, but with a real world signal source with a relatively poor VSWR, there could be significant dips in the frequency response, especially when using a reasonably long piece of coax cable to make the connection to the counter.
However, not many people will use a frequency counter at these frequencies for real world applications in 2024. If you only plan to use it to 10GHz or even 18GHz I wouldn't worry too much about the BNC connector unless you actually end up with a frequency response problem one day.
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Systron-Donner 6054B ¨C the 20 MHz -24 GHZ connector on stock models certainly looks like an SMA to me. The 20 Hz -20 MHZ input is a BNC. The S-D catalog calls out (verbatim) ¡°SMA-3MM. Other input connectors available on special order.¡±
A BNC modification would nicely fit into the hole made for a SMA if a slight modification to the hole were made with no trace of any hacking.
Greg
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The datasheet for that 6054B counter does state that the input is normally an SMA connector. However, it also states that other connector types are available on special order.
A standard BNC connector would be an odd choice to fit here though...
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Probably only about 6 gadzillion were used on routers before the inverse SMA became popular... But, no, they didn't catch on in the test equipment world. -Chuck Harris On Sat, 29 Jun 2024 13:32:04 -0700 "Jinxie via groups.io" <paul666@...> wrote: TNC are several orders of magnitude better than BNC IIRC. Far more
phase stable (that's another aspect we haven't mentioned yet). Shame
they never really caught on; bit like Betamax and VHS. :(
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From what I have seen, the 6054B can have either a SMA style, or an N style depending on the top frequency. Never BNC. If yours has a BNC on the microwave input, then someone must have changed it... Probably because they broke the SMA style connector. I say SMA style, because it is more probably an APC 3.5. -Chuck Harris On Sat, 29 Jun 2024 12:54:19 -0700 "Jinxie via groups.io" <paul666@...> wrote: 6054B and I can't post any pictures right now I'm afraid. It doesn't
appear that the BNC has been changed from SMA; looks original and why
would anyone do such a thing anyway? Does seem an odd choice!
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TNC are several orders of magnitude better than BNC IIRC. Far more phase stable (that's another aspect we haven't mentioned yet). Shame they never really caught on; bit like Betamax and VHS. :(
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In the past, I have fed 13GHz into one of these Agilent scopes that use BNC inputs and it displayed the 13GHz signal (from an old HP 83752A generator) just fine. There was some loss, but that is to be expected in the cable and the scope front end as it was a 13GHz rated scope. It was probably less than 3dB loss but I can't remember now.
These 13GHz BW scopes (40Gsa/s sample rate) have a fixed 50 ohm input via the BNC connectors on the front panel. They are quite old scopes, there has been one at work for many years and I use it now and again for TD stuff.
I'm not sure what the upper frequency limit would be for these custom BNC connectors if they were used for a counter rather than a 13GHz scope. It's going to be a bit more than 18GHz but it might not manage 22GHz...
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There was an option to move the high frequency input to the rear panel, leaving only a BNC on the front panel. Might that be what you have?
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On Jun 29, 2024, at 2:54?PM, Jinxie via groups.io <paul666@...> wrote:
?6054B and I can't post any pictures right now I'm afraid. It doesn't appear that the BNC has been changed from SMA; looks original and why would anyone do such a thing anyway? Does seem an odd choice!
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I'd expect a 22GHz counter to typically use a 3.5mm connector, but it could also use SMA or N connectors at a push.
Note that the highest (frequency) rated BNC connectors I've seen are rated to 18GHz but these are specials made by Agilent. These connectors look just like a BNC and can mate with a standard BNC connector but they are gold plated and have a precision inner connector made with better defined dimensions and a better mating technology compared to a standard BNC connector. These special BNC connectors could be used as the main channel inputs of a 13GHz scope for example.
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It's worth knowing that the variant of the display in the 3562 is different from most other 1345A units. The 3562A service manual includes schematics and these are the best ones to use.? Foolishly I started with (several different)1345A manuals which were excellent from a general understanding point of view of the interface and commands but quickly throws up lots of specific differences on the boards.
The self test (just remove the IDC cable) with Pikes Peak is a very good place to begin.
Alan
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Chuck, it absolutely *cannot* have been an N type at any time in its life or there'd be a ring of some sort around the BNC as they're smaller than the hole an N type needs.
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6054B and I can't post any pictures right now I'm afraid. It doesn't appear that the BNC has been changed from SMA; looks original and why would anyone do such a thing anyway? Does seem an odd choice!
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Forgot to say, the 2442 goes to 26.5GHz.
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First:
BNC and N WILL NOT mate properly. while the main dimensions of the center parts are the same (they are 7mm class connectors) the center pin of the N connector is lrger than the BNC center pin. If you push a N male onto a BNC frmale you can damage the BNC.
I am also very surprised that any commercial frequency counter would use a BNC connector for a 8 GHz input never mind at 20GHz. All 7mm connectors are limited to 18GHz for predictable performance. Most N types got to 12GHz but special precision versions go higher. As an example the 20GHz Marconi 2440 counter uses a precision N type for the microwave input. The otherwise identical 2442 uses a 3.5mm (like an SMA but air dielectric).
What model is the counter? Can you post a picture of the connector niclding the area around the connector?
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Pete_G4GJL
Jinxie