[time-nuts] Re: looking for MITREX modem manual/documentation

[Lester Veenstra]

Good luck;
This was one of the first projects I worked on when I joined Comsat Labs.
  Les

Lester B Veenstra  K1YCM  MØYCM  W8YCM   6Y6Y
lester at veenstras.com

452 Stable Ln (HC84 RFD USPS Mail)
Keyser WV 26726

GPS: 39.336826 NÂ  78.982287 W (Google)
GPS: 39.33682 NÂ  78.9823741 W (GPSDO)


Telephones:
Home:Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â  Â  +1-304-289-6057
US cell                    +1-304-790-9192 
Jamaica cell:Â Â Â Â Â Â Â Â Â Â  +1-876-456-8898 
 


-----Original Message-----
From: jeanmichel.friedt at femto-st.fr [mailto:jeanmichel.friedt at femto-st.fr] 
Sent: Friday, March 25, 2022 1:45 PM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] Re: looking for MITREX modem manual/documentation

Thank you all for the very fruitful exchanges and providing the references
I was looking for (by private email).

FYI I indeed tried the brute force search as documented at
https://github.com/oscimp/gr-satre/tree/main/reverse_code
but wanted to try to find some formal documentation demonstrating the
orthogonality
of the codes beyond "trust me, we selected the best codes for maximum
orthogonality".

Also if anyone is interested, I am looking into receiving TWSTFT exchange
using TV
parabola (of course receiving only !). That is for fun since, for work the
modem is
being assembled indeed, but that is off topic :)

Thank you very much, Jean-Michel

--
JM Friedt, FEMTO-ST Time & Frequency, 26 rue de l'Epitaphe, 25000 Besancon,
France

March 25, 2022 5:40 PM, "Lux, Jim" <jim at luxfamily.com> wrote:

> On 3/25/22 7:45 AM, Azelio Boriani wrote:
> 
>> From the paper "PRESENT STATE OF LONG DISTANCE TIME TRANSFER VIA
>> SATELLITES WITH APPLICATION OF THE MITREX - MODEM", Hartl specifies
>> that "The PN-code is a truncated maximum length sequence of period
>> 10.000, instead of the 16.383 chips". In the Xilinx application note
>> XAPP052, we can find that the taps for an MLS of 14 bits should be
>> 14,5,3,1. In the paper "GEOSTATIONARY SATELLITE POSITION DETERMINATION
>> FOR COMMON-VIEW TWO-WAY TIME TRANSFER MEASUREMENTS" there is an
>> introduction that suggests the MITREX 2500 modem has a variable
>> pseudorandom noise sequence. Maybe the modem was built in different
>> versions wrt the PN sequence generation.
> 
> There's a fair number of of maximal sequences of length 2^14-1 . And
> it's possible that they chose a non-maximal sequence that had "better"
> properties. Maximal sequences will have a run of N ones and (N-1) zeros,
> for instance, which might not have enough transitions per unit time to
> let the receiver get a good lock.  Or they picked a "good" 10kbit
> sequence in the middle of a maximal sequence.
> 
> It could also be a composite code (the XOR of multiple PN sequences) -
> none of the papers seems to say anything about tap configurations.
> 
> I'd suggest seeing if you could find an email address for Professor
> Hartl - He'd be 94 now.  I think he retired from Univ Stuttgart in 1990.
> 
> At 2 Mchip/second, you could pretty easily build a MITREX type modem
today.
> 
>> On Fri, Mar 25, 2022 at 2:37 PM <jeanmichel.friedt at femto-st.fr> wrote:
>>> Dear community,
>>> I am trying to find historical documents describing the pseudo random
sequences used
>>> in the SATRE Two-Way Satellite Time and Frequency Transfer (TWSTFT)
modem.
>>> K. Imamura & F. Takahashi (Two Way Time Transfer Via a Geostationnary
Satellite,
>>> J. of the Comm. Research Lab., 39(1), March 1992) describe the code
structure
>>> (14-bit long pseudo random sequence truncated to 10000 bit length) but
the
>>> generator polynomial coefficients are not given. I have not been able to
find this
>>> information in Timetech's SATRE manual nor in the publicly available
literature.
>>> This paper cites "P. Hartl, A modem for microwave time and ranging
experiments
>>> via telecommunication satellites, MITREX2500 Manual, Jan 1989" which I
am unable
>>> to locate.
>>> Would anyone have such a document, or at least could tell me whether the
generator
>>> polynomials are described there? Alternatively, does anyone have a
description of these
>>> 14-bit polynomial generators?
>>> 
>>> Thanks, Jean-Michel
>>> 
>>> --
>>> JM Friedt, FEMTO-ST Time & Frequency, 26 rue de l'Epitaphe, 25000
Besancon, France
>>> _______________________________________________
>>> time-nuts mailing list -- time-nuts at lists.febo.com -- To unsubscribe
send an email to
>>> time-nuts-leave at lists.febo.com
>>> To unsubscribe, go to and follow the instructions there.
>> 
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at lists.febo.com -- To unsubscribe send
an email to
>> time-nuts-leave at lists.febo.com
>> To unsubscribe, go to and follow the instructions there.
> 
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com -- To unsubscribe send
an email to
> time-nuts-leave at lists.febo.com
> To unsubscribe, go to and follow the instructions there.
_______________________________________________
time-nuts mailing list -- time-nuts at lists.febo.com -- To unsubscribe send an
email to time-nuts-leave at lists.febo.com
To unsubscribe, go to and follow the instructions there.