Re: [time-nuts] unknown GPSDO

[Tim Shoppa]

The original Brooks Shera unit was 20 years ago and is pretty well
documented in QST and his website. In the original the loop filter
timeconstant was set by jumpers or DIPswitches. And I think the EFC gain
factor was set somewhere else (DIPswitch? Resistor network? Both?)

Shera's webpage documents some improvements and changes up through 2001 but
there have been an incredible number of variations out there in the wild as
folks move parameters that used to be set in hardware/DIPswitches to
firmware with LCD config screens etc. I think the OP's unit shows a decade
or more of evolution past what Shera documents.

Is there a "Brooks Shera GPS family tree" out there showing recent
evolution of the design?

Tim N3QE

On Tue, Jul 18, 2017 at 11:10 AM, David C. Partridge <
david.partri...@perdrix.co.uk> wrote:

> ISTR that you started it with a short time constant to get locked,  and
> once you had lock you would increase the time constant in a few steps to a
> final value of (say) 1000s or so.
>
> Dave
>
> -Original Message-
> From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Volker
> Esper
> Sent: 18 July 2017 14:15
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] unknown GPSDO
>
> Thanks so far. I will have a look at the docs.
>
> The machine is running well, particularly the OCXO is performing very good
> when free running (without GPS signal). It is stable and its ADEV looks
> good (2E-10 at 10s). Not so the overall ADEV (when GPS locked)
> (1E-5 at 10s). It seems to not having the right filter time constant what
> had to be much longer. As I understand the documents, the filter constant
> can be programmed and I will experiment whith that this afternoon.
>
> Thank you
>
> Volker
>
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Re: [time-nuts] unknown GPSDO

[David C. Partridge]

ISTR that you started it with a short time constant to get locked,  and once 
you had lock you would increase the time constant in a few steps to a final 
value of (say) 1000s or so.

Dave

-Original Message-
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Volker Esper
Sent: 18 July 2017 14:15
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] unknown GPSDO

Thanks so far. I will have a look at the docs.

The machine is running well, particularly the OCXO is performing very good when 
free running (without GPS signal). It is stable and its ADEV looks good (2E-10 
at 10s). Not so the overall ADEV (when GPS locked)
(1E-5 at 10s). It seems to not having the right filter time constant what had 
to be much longer. As I understand the documents, the filter constant can be 
programmed and I will experiment whith that this afternoon.

Thank you

Volker

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Re: [time-nuts] unknown GPSDO

[Volker Esper]

Thanks so far. I will have a look at the docs.

The machine is running well, particularly the OCXO is performing very
good when free running (without GPS signal). It is stable and its ADEV
looks good (2E-10 at 10s). Not so the overall ADEV (when GPS locked)
(1E-5 at 10s). It seems to not having the right filter time constant
what had to be much longer. As I understand the documents, the filter
constant can be programmed and I will experiment whith that this afternoon.

Thank you

Volker

Am 17.07.2017 um 16:36 schrieb EB4APL:
> Hi Volker,
> 
> Browsing on my documentation I found that 402NE wast the last version of
> Brooks Shera's (W5OJM) code for the PIC, made in collaboration with
> Bob Leichner (WO6W). Probably this ham was one of Shera´s friends who
> developed the last version and published the sources.
> 
> I include below the instructions that Shera sent me with version 402NE
> 
> Regards,
> 
> Ignacio, EB4APL
> 
> 
> 
> W5OJM GPS-DISCIPLINED FREQUENCY STANDARD...
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Re: [time-nuts] RS232 output on a 53181A

[Angus]

Hi,

Also, since it's a p rather than any other character, my guess is that
it probably was deliberate - although whether it was meant to be
shipped like that is another question.

Angus.


On Wed, 12 Jul 2017 11:56:24 -0400, you wrote:

>Well ASCII * is 2a in Hex, p is 70 so that seems an unlikely substitution
>for a failing EPROM.
>
>But 0 is 30 Hex, only one bit different from p.
>
>On Wed, Jul 12, 2017 at 10:39 AM, Angus  wrote:
>
>> Hi,
>>
>> I've just been using an Agilent 53181A, but the serial output is not
>> quite what I had expected. On the 53131A's that I've used the
>> placeholder character on the RS232 output is an asterisk, but with
>> this unit it is a lower case 'p'. Where the 53131A sends '2,*** u',
>> this 53181A send '2,ppp u'. The only references to a placeholder that
>> I saw in the manuals referred to an asterisk.
>>
>> The firmware version is 4613.
>>
>> Anyway, just wondering if anyone knows if this is correct, or maybe
>> it's just the EPROM starting to fail.
>>
>> Thanks,
>> Angus.
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[time-nuts] 5370B Input Board Repair [WAS: 5370B Question / help needed]

[Thomas Allgeier]

Hello All Again,



I’ve got my 5370B going now and in the process made a “discovery” which I 
thought might be worth sharing:

The A3 input board is a through-hole PCB with a few SMD capacitors and 
resistors on the reverse of the “switch area”. It turns out that on my 5370 
(2410A00777) these components are not soldered, but fitted with conductive 
adhesive. I first thought it was solder with a black coating but under a 
microscope it is clear that it is not solder at all. Most probably it is a 
mixture of epoxy and silver particles, or a similar compound. So no going over 
joints with a fine iron…

Inspecting all this carefully under the microscope I discovered that the 
“joints” on 2 resistors (R23 and R56) had cracked. As you know this board gets 
heat from the hybrid amplifier IC’s and due to the way the board is mounted to 
the front panel I guess it sees thermal stressing when the instrument warms up 
and cools down. While this obviously lasts a long time it looks that on my unit 
the adhesive has eventually cracked in places. (Vigorous switch activation and 
pressing / pulling on the switch handles also won’t be helpful in this 
respect…) One of the resistors just fell off at the slightest touch with fine 
tweezers.



Anyhow, after removing the offending components, cleaning the pads of the 
adhesive, and soldering replacements in place, we have a perfect 99.9x ns with 
the 10 MHz on the commoned inputs. Happy days!



So if any of your 5370’s have the kind of intermittent fault I described (and 
one or two other people seem to have reported) or instability that seems to 
originate from the A3 board – check the joints around the SMD’s.



I wonder why / how it ended up having the adhesive instead of solder – were 
earlier / later instruments the same, or was this a build change introduced at 
a certain period?



Hope the above is of help to somebody else,

Thomas.



Message: 1
Date: Sat, 15 Jul 2017 21:54:47 +0100
From: Thomas Allgeier 
To: Discussion of precise time and frequency measurement

Subject: Re: [time-nuts] 5370B Question / help needed
Message-ID: