I could not agree more, having been burned once or twice.
One batch of "50 Ohm" cables was clearly marked 75 Ohms when received. These
used some form of
relatively high resistance foil shield and a drain wire for the outer
conductor. The high resistance permitted
a ground loop with hum on my 10 MHz reference thus FMing my signal generator.
A couple of things to note:
Measure the DC resistance between the connector bodies it should be way less
than 1 Ohm, perhaps
0.1 ohm above what you see with the probes shorted.
The previous regarding RG-58 apply unless the cable is labeled with a
manufacturers part number and that is stated in the vendors spec -
Such as
BELDEN 8262 RG-58U Coaxial BNC M/M Patch Cable 10FT.
RG58 C/U MIL C17 50 OHMS stamped on the cable.
These were from - Digital Connections - cablesellforl...@yahoo.com and
purchased via eBay. The price was very reasonable.
Testing with a HP ANA showed very low VSWR and the expected insertion loss up
to 1 GHz. Shield resistance was very low, as expected. I have used these in
lengths from 3 ft to 20 ft with no difficulty.
The key here is the Belden part number in the vendors ad that can be checked
to see what you are getting. The MIL SPEC and RG58 etc was stamped on the
cables when received.
For outstanding performance use RG-223 which is slightly larger than RG-58 and
is a 50 Ohm cable
having a very dense double sliver plated braid shield.
You can buy these made up for a small fortune or buy an odd lot of RG-223 on
eBay and make your own. Pasternak has the connectors with the appropriate
diameter nuts and collars. The connectors for Rg-58
are had to make work on RG-223. Connectors for Type N and SMA are also
available.
Installing clamp style connectors on RG-223 requires a certain amount of
passion (and a stainless steel welders tooth brush to comb the braid) but hey,
no pain no gain.
-73 john k6iql
-----Original Message-----
From: time-nuts-request <time-nuts-requ...@febo.com>
To: time-nuts <time-nuts@febo.com>
Sent: Sun, Mar 3, 2013 11:00 am
Subject: time-nuts Digest, Vol 104, Issue 13
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When replying, please edit your Subject line so it is more specific
than "Re: Contents of time-nuts digest..."
Today's Topics:
1. Re: Don't use cheap cables -- a cautionary tale (Bob Camp)
2. Re: webcam app to watch for and time stamp changes
(Magnus Danielson)
3. Re: Don't use cheap cables -- a cautionary tale (John Ackermann)
4. Re: Don't use cheap cables -- a cautionary tale (Kevin Rosenberg)
5. Re: Don't use cheap cables -- a cautionary tale (Bob Camp)
6. Re: Don't use cheap cables -- a cautionary tale (Jim Lux)
7. Re: webcam app to watch for and time stamp changes (cfo)
----------------------------------------------------------------------
Message: 1
Date: Sun, 3 Mar 2013 10:10:38 -0500
From: Bob Camp <li...@rtty.us>
To: Discussion of precise time and frequency measurement
<time-nuts@febo.com>
Subject: Re: [time-nuts] Don't use cheap cables -- a cautionary tale
Message-ID: <335213bf-bbf3-44bd-9a7a-0bd481028...@rtty.us>
Content-Type: text/plain; charset=iso-8859-1
Hi
By any chance is the connector a BNC? They have been known to create similar
looking issues.
Bob
On Mar 3, 2013, at 9:59 AM, John Ackermann <j...@febo.com> wrote:
> I was measuring two OCXO and was getting some quite unusual results -- a
symmetrical frequency cycling of several more than 1e11 p-p, with a period of
around 15 seconds.
>
> I removed an RG-58 3 foot jumper cable that fed 5 MHz from the rear panel of
another OCXO to a patch panel (where it was terminated in 50 ohms), and the
noise quieted right down. See the attached frequency plot.
>
> The other OXCO had a similar jumper cable in the path, and although the two
cables were not parallel to each other for any significant distance, there was
still enough signal radiation and pickup to cause a nasty problem.
>
> Lesson learned -- use only double-shielded cable in the oscillator rack (and
in any RF measurement path) from now on.
>
> John
> <austron-fts-beat-note.png>_______________________________________________
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
------------------------------
Message: 2
Date: Sun, 03 Mar 2013 16:29:15 +0100
From: Magnus Danielson <mag...@rubidium.dyndns.org>
To: time-nuts@febo.com
Subject: Re: [time-nuts] webcam app to watch for and time stamp
changes
Message-ID: <51336c4b.4030...@rubidium.dyndns.org>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
On 03/03/2013 03:46 PM, Jim Lux wrote:
> On 3/3/13 1:00 AM, Poul-Henning Kamp wrote:
>> Content-Type: text/plain; charset=ISO-8859-1
>> --------
>> In message <657D7F7CC03849419A2A90752E6A60A6@pc52>, "Tom Van Baak"
>> writes:
>>
>>> When playing with watches a while ago I tried to pick up any 32
>>> kHz signal but failed. Those with 1 Hz stepper motors were easy,
>>> but LED or LCD displays were too electro/magnetic/acoustic quiet
>>> for me to ever detect anything.
>>
>> Most LCD and LED clocks have a shielding metal-coating on the front
>> glass, exactly to eliminate all EMI/EMC issues.
>>
>
> Yes, but perhaps there's enough leakage to make this work. After all,
> the EMI requirement (assuming it's running at 32 kHz) isn't particularly
> stringent and because the fob is small, the radiated field at any
> distance is going to very small. OTOH, I can put a probe or coil right
> on or around the fob.
>
> I'll let you all know what I detect when I try it tomorrow.
An electrostatic shield will not contain the H-field from the shifting
currents.
Cheers,
Magnus
------------------------------
Message: 3
Date: Sun, 03 Mar 2013 10:46:10 -0500
From: John Ackermann <j...@febo.com>
To: Discussion of precise time and frequency measurement
<time-nuts@febo.com>
Subject: Re: [time-nuts] Don't use cheap cables -- a cautionary tale
Message-ID: <51337042.4020...@febo.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Yup, they are BNC (by necessity). I'm still experimenting but it may be
an ill-fitting connector on the cheap patch cable. Switching to a
better quality cable seems to have solved the problem, one way or the other.
John
----
Bob Camp said the following on 03/03/2013 10:10 AM:
> Hi
>
> By any chance is the connector a BNC? They have been known to create similar
looking issues.
>
> Bob
>
> On Mar 3, 2013, at 9:59 AM, John Ackermann <j...@febo.com> wrote:
>
>> I was measuring two OCXO and was getting some quite unusual results -- a
symmetrical frequency cycling of several more than 1e11 p-p, with a period of
around 15 seconds.
>>
>> I removed an RG-58 3 foot jumper cable that fed 5 MHz from the rear panel of
another OCXO to a patch panel (where it was terminated in 50 ohms), and the
noise quieted right down. See the attached frequency plot.
>>
>> The other OXCO had a similar jumper cable in the path, and although the two
cables were not parallel to each other for any significant distance, there was
still enough signal radiation and pickup to cause a nasty problem.
>>
>> Lesson learned -- use only double-shielded cable in the oscillator rack (and
in any RF measurement path) from now on.
>>
>> John
>> <austron-fts-beat-note.png>_______________________________________________
>> time-nuts mailing list -- time-nuts@febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>
> _______________________________________________
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
------------------------------
Message: 4
Date: Sun, 3 Mar 2013 09:00:03 -0700
From: Kevin Rosenberg <ke...@rosenberg.net>
To: Discussion of precise time and frequency measurement
<time-nuts@febo.com>
Subject: Re: [time-nuts] Don't use cheap cables -- a cautionary tale
Message-ID: <032c3cb2-5c27-4338-8196-697415f7e...@rosenberg.net>
Content-Type: text/plain; charset=iso-8859-1
On Mar 3, 2013, at 7:59 AM, John Ackermann <j...@febo.com> wrote:
> Lesson learned -- use only double-shielded cable in the oscillator rack (and
in any RF measurement path) from now on.
I've learned that lesson as well. John Miles said that RG-58 is occasionally
referred to as 'soaker hose'.
Kevin
------------------------------
Message: 5
Date: Sun, 3 Mar 2013 11:08:45 -0500
From: Bob Camp <li...@rtty.us>
To: John Ackermann <j...@febo.com>
Cc: Discussion of precise time and frequency measurement
<time-nuts@febo.com>
Subject: Re: [time-nuts] Don't use cheap cables -- a cautionary tale
Message-ID: <6a29d6e9-b3ba-4e3c-b10b-e91f30816...@rtty.us>
Content-Type: text/plain; charset=windows-1252
Hi
BNC's suffer from shield separation issues and from basic wear out on the
connector it's self. Cheap coax = shield seperation. On the connector its self
it's either plating or loss of spring in the fingers. The best solution is to
cut the connector off the cable. That way at least it doesn't mess you up a
second time. Once you get a big enough pile of single ended cables, it's time
to
get out the crimp tool?.
Bob
On Mar 3, 2013, at 10:46 AM, John Ackermann <j...@febo.com> wrote:
> Yup, they are BNC (by necessity). I'm still experimenting but it may be an
ill-fitting connector on the cheap patch cable. Switching to a better quality
cable seems to have solved the problem, one way or the other.
>
> John
> ----
> Bob Camp said the following on 03/03/2013 10:10 AM:
>> Hi
>>
>> By any chance is the connector a BNC? They have been known to create similar
looking issues.
>>
>> Bob
>>
>> On Mar 3, 2013, at 9:59 AM, John Ackermann <j...@febo.com> wrote:
>>
>>> I was measuring two OCXO and was getting some quite unusual results -- a
symmetrical frequency cycling of several more than 1e11 p-p, with a period of
around 15 seconds.
>>>
>>> I removed an RG-58 3 foot jumper cable that fed 5 MHz from the rear panel
>>> of
another OCXO to a patch panel (where it was terminated in 50 ohms), and the
noise quieted right down. See the attached frequency plot.
>>>
>>> The other OXCO had a similar jumper cable in the path, and although the two
cables were not parallel to each other for any significant distance, there was
still enough signal radiation and pickup to cause a nasty problem.
>>>
>>> Lesson learned -- use only double-shielded cable in the oscillator rack
>>> (and
in any RF measurement path) from now on.
>>>
>>> John
>>> <austron-fts-beat-note.png>_______________________________________________
>>> time-nuts mailing list -- time-nuts@febo.com
>>> To unsubscribe, go to
>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>> and follow the instructions there.
>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts@febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
>
------------------------------
Message: 6
Date: Sun, 03 Mar 2013 08:30:43 -0800
From: Jim Lux <jim...@earthlink.net>
To: time-nuts@febo.com
Subject: Re: [time-nuts] Don't use cheap cables -- a cautionary tale
Message-ID: <51337ab3.6020...@earthlink.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
On 3/3/13 8:00 AM, Kevin Rosenberg wrote:
> On Mar 3, 2013, at 7:59 AM, John Ackermann <j...@febo.com> wrote:
>> Lesson learned -- use only double-shielded cable in the oscillator rack (and
in any RF measurement path) from now on.
>
> I've learned that lesson as well. John Miles said that RG-58 is occasionally
referred to as 'soaker hose'.
>
RG-58 (which by the way, is a spec that officially no longer exists as
part of MIL-C17-28, ditto for RG-8, RG-213, etc. The military apparently
doesn't use PVC insulated wire any more.) comes in myriad forms all of
which bear a passing resemblance to each other. (leaving aside the
RG-58A, RG-58, RG-58C differences).
The term seems to be used for any 50 ohm single shield coax that's about
0.20 inch in diameter with solid polyethylene insulation. You really
need to look at the specific model number to know what the shielding
looks like. It could be anything from a very loose weave of thin copper
strands to something nice and dense.
------------------------------
Message: 7
Date: Sun, 3 Mar 2013 16:52:06 +0000 (UTC)
From: cfo <xne...@luna.dyndns.dk>
To: time-nuts@febo.com
Subject: Re: [time-nuts] webcam app to watch for and time stamp
changes
Message-ID: <kgvv3m$ug7$1...@ger.gmane.org>
Content-Type: text/plain; charset=UTF-8
On Sat, 02 Mar 2013 11:33:02 -0800, Jim Lux wrote:
> I am interested in the timing behavior of my RSA fob, which changes
> every 60 seconds. Since I'm not about to open it up and probe inside, I
> was wondering if someone had a clever way, say using a USB web cam, to
> log the changes over a 48 hour period. You'd point the web cam at the
> fob, and it would log the time when the display changes Or one might
> even be able to look at the blinking 1 pps indicator using a light and
> photocell or something..
Isn't this "Just what the doctor ordered"
http://smallhacks.wordpress.com/2012/11/11/reading-codes-from-rsa-
secureid-token/
CFO
------------------------------
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