[time-nuts] update on LTE-Lite

SAIDJACK at aol.com SAIDJACK at aol.com
Mon Nov 24 14:40:08 EST 2014

So to verify the initial results we saw we tested another 10MHz DIP-14 unit 
 on a different ADEV test-set, and the results are similar.
See the attached ADEV plot of a random unit.
This was actually the synthesized output from the board set to 20MHz from  
the 10MHz TCXO, then fed through a divide-by-2 CMOS circuit utilized as a 50 
 Ohms buffer then anaylzed by our TSC5125A.
It shows that the synthesizer output nicely follows the TCXO, and it  shows 
the ADEV performance of the DIP-14 TCXO.
In a message dated 11/22/2014 18:23:35 Pacific Standard Time,  
time-nuts at febo.com writes:


I would not worry too much about the RTV, more about  damaging the nice  
TCXO. That part is by far the most expensive and  valuable component on the 
boards. It's not your good old $10 style  TCXO.. 

We were not aware and did not know of the beat frequency  causing some  
spurs until the day I posted my findings and  suggestions, but there is an 
way around the issue as I had  discussed at that time as well.

The easiest way to avoid the beat  frequency spurs when using an external  
oscillator is to use a  splitter with high isolation on the RF output of 
oscillator, and  to put an LC filter on the EFC pin of that oscillator. One 
(CMOS   compatible) output of the splitter goes to the LTE-Lite MMCX 
connector,  the  other output can be used for your circuitry or instruments 

Depending on the isolation capability of the splitter I bet there  won't be 
anything coming through. Instead of a passive splitter a  simple CMOS gate 
as a  buffer also provides massive amounts of  isolation from the 20MHz RF  
floating around the LTE Lite  board.

In either way the spurs are quite low if I remember correctly,  so even  a 
passive splitter with 40dB or so isolation will likely  push the spurs 
the noise floor of the oscillator I would  think. The secondary path into 
OCXO could be through the EFC output,  and that can be easily filtered out 
by  using a small RC or LC  filter, say 22uH into a 100nF cap mounted onto 
the OCXO  EFC pin.  That should squelch any RF on the EFC line. Since most 
OCXOs have an  RC  filter built into the EFC pin anyways (usually a 30K 
Ohms or  
higher series  resistor into the capacitance of the varactor diode at  the 
least) I don't think  much of the 20MHz would come through the  EFC line, 
of it probably through  the RF pin.

There is a  220 Ohms series resistor on the EFC output of the LTE-Lite  
anyways,  so just putting a 10nF to ground on the OCXO EFC pin would 
create a low pass filter with a 70KHz cut off frequency, so that single  
cap by  
itself may be sufficient already to get rid of any 20MHz RF  floating 
the  EFC line. Definitely use a shielded coax cable  for the EFC line 
though, not just  a simple wire.

On the 10MHz  boards the DIP-14 TCXO is soldered onto the board for best   
performance and mechanical stability, but since it only has four pins in  a 
DIP-14 configuration it is very easily removed from the PCB with a  proper  
solder-iron if that is  desired.


Begin forwarded  message:

Cc: _time-nuts at febo.com_  (mailto:time-nuts at febo.com) 
Subject:  Re: [time-nuts] update on  LTE-Lite
Reply-To: _GandalfG8 at aol.com_ (mailto:GandalfG8 at aol.com) ,  Discussion of 
precise  time and frequency measurement  <_time-nuts at febo.com_ 
(mailto:time-nuts at febo.com)  >

Hi Said,

Many thanks for your   reply.

I'd realised that R2 and R3 were in  the paths of  alternative power feeds  
but had managed  to convince myself  that both resistors were shown to be  
fitted  in your auction  photos, although I can now see  quite clearly that 
R2  is  fitted, R3 isn't,  whoops:-)

I was hoping that removing  the  TXCO might be reasonably straightforward, 
was after  all  your suggestion:-), but am now concerned that the RTV might 
have  flowed under any components perhaps not fully  seated and  didn't 
to take the  risk of damaging  anything. I'd also  hoped it might prove 
possible to remove  the onboard TCXO power by  breaking one of the tracks 
LTE-Lite module  itself  but it sounds like that might  have been a bit too 

Whilst I'm  pretty sure I would have stuck with  the 20MHz version  anyway, 
the initial enthusiastic rush did  mean nearly 40 of us had  already  
them before your  comments regarding  the harmonic  mixing and the 
suggestion to  
use the  19.2MHz version reached  the list, so to some extent at  least 

might help explain the  numbers:-)

Anyway,  thanks very much  again for making these available, I certainly   
don't  see this as a significant issue so it's time to dive in  and  worry  
the finer details  later.

Just  out of interest, on the 10MHz  version without the onboard  TCXO,  
the DIL  oscillator end up socketed or   soldered?



In  a  message dated 22/11/2014 18:01:18 GMT Standard Time,   
_saidjack at jackson-labs.com_ (mailto:saidjack at jackson-labs.com)    writes:


CC'ing  time nuts..

R2 and R3  are  stuffing options, see the schematics in the user manual.   
Typically you don't have to solder anything. The  default is set for  the  
low-noise 3.0V to be fed to  the DIP-14 tcxo for best   performance.

On removing  the SMT Tcxo, this is not easy, but  possible with a heat gun. 
Its easy to melt the adjacent switches  though when  doing that. The RTV 
it  should just peel  off, but  we have not tried that yet. There is no way 
just  remove power to the internal Tcxo   unfortunately.

This is why  I had suggested the 19.2MHz  version for people who want to  
the external oscillator  option, because that won't beat  with your  
oscillator close-in.  I was a bit surprised  that so few of those 19.2MHz 
units  sold  
compared to  the significant numbers for 10/20MHz units. In either  case I  
think the resulting beat spurs are typically lower  than  many other GPSDOs 
oscillators have in their  spurs, the  CSAC with its spurs comes to  mind..

Hope that   helps,

Sent from my  iPad

On Nov 22, 2014, at 6:08,  __GandalfG8 at aol.com_ (mailto:GandalfG8 at aol.com) 
(mailto:GandalfG8 at aol.com)   

Hi  Said,

Sorry to bother you  again, I'm not  sure is this is an oversight or  
deliberate but  I've  just noticed that R2 has not been fitted to my   
I'm a bit concerned as this will   affect power to the external  oscillator 
and R2 would  be  difficult to fit now that SW2 is installed.
I may have  missed this if  it was mentioned on the Time-Nuts list  but  
there's a lot there  to look through so thought it best to  ask you   



In  a message  dated 30/10/2014 23:30:40 GMT Standard Time, 
__saidjack at jackson-labs.com_  (mailto:saidjack at jackson-labs.com) _  
(mailto:saidjack at jackson-labs.com)   writes:

Hello  everyone, 
We wanted to give you an  interim update on the  LTE-Lite  Evaluation kit 
builds. We are  making good  progress on the assembly. We are  expecting to 
within the announced time frame, and are guiding the   factory on a daily 
We are  using the time to improve the  firmware and have  made some 

with the help and efforts  of a very well-known Time Nut  (thanks much!) 
I am certain will  identify himself  in due time.  This development 
has  revealed a  sensitivity in the GPS  receiver: the unit should not  be  
changed from mobile mode to Position Hold  (Timing)   mode ROM/Flash 
firmware or 
vice versa while power is   enabled,  this could lead to Flash memory 
corruption.  We are  thus shipping the unit  with a solder jumper that will 
soldering-in two pins to get out of  Timing mode and  into  mobile mode so 
as to 
avoid the possibility of a user   accidentally inserting a jumper with 
supplied  to the unit,  which  could then corrupt the GPS Flash memory. We 
also been able to upgrade  the GPS Flash firmware in  close  cooperation 
the vendor of the GPS  receiver  to make it  more optimal for operation in 
GPSDO, and these  efforts have given  us a GPS Flash firmware release that  
works well with  our GPSDO  algorithms and TCXOs. We  will upgrade all of 
GPS  receivers  prior to  shipment with this specialized firmware  release. 
We also  have some good news on the 10MHz versions of   the board: the 

DIP-14 TCXOs are scheduled to arrive at our  factory  in about 5 weeks, so 
that will pull-in the delivery   schedule  significantly. We will continue 
keep  track of  the schedule and update  you with any changes.  

Lastly there  has been some fairly intense  discussion recently about 
counter-fit  FTDI serial  chips getting  permanently disabled by the latest 
software drivers and thus  rendering affected   equipment unusable. Many 
have been published on  Time-Nuts  so please consult the archives for more  
information on this   issue. 
We use  FTDI chips on many of our products, such as the   CSAC GPSDO,  
Mini-JLT, LC_XO Plus kit, and also this LTE-Lite Eval  kit.  We  are 
announce that we have verified  with  our suppliers that all  of our 
shipments in 
the  past  and in the future have and will continue to  use genuine FTDI  
Close inventory control and counter-fit policies   are  one advantage of 
manufacturing in the USA versus in  Asia.  
More later,  
Said  Jackson 
Jackson Labs  Technologies,  Inc.  
1635 Village Center Circle, Suite   150  
Las Vegas, NV 89134  
Tel. (408)  596-0600 
Fax.  (702) 233-1073 
__saidjack at jackson-labs.com_  (mailto:saidjack at jackson-labs.com) _  
(mailto:saidjack at jackson-labs.com)  
__www.jackson-labs.com_  (http://www.jackson-labs.com/) _ 

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