Re: LF: Simple coherent frequency generator

[Riccardo Zoli <riccardozoli80@gmail.com>]

Hi Markus, Domenico, Stefan, LF

I'm trying to receive with a W&G SPM-31 selective voltmeter tuned @ 137500 (stand-alone, without external reference). A GPS module NEO-M8N inject in antenna a 136500 @ -45dBm signal (became a 1 kHz reference audio for SL's SR correction).

I'm looking for the simplest method to receive coherent signals.

All the best

73 de Riccardo IW4DXW

Il 07/Lug/2017 10:09, "Markus Vester" <markusvester@aol.com> ha scritto:

Thank you very much Ric for this most interesting hint.

Unfortunately I couldn't find the two jpg images, they might have been in an attachment that didn't make it through the reflector. Would it be possible to upload them to a website and share the links?

One note regarding excitation at double frequency: Make sure that the XOR modulation is applied after the final divider, because otherwise the phase difference would be halved (+-90 instead of +-180 degrees) and also ambiguous.

Best 73,
Markus (DF6NM)

-----Ursprüngliche Mitteilung-----
Von: Riccardo Zoli <riccardozoli80@gmail.com>
An: LF Group <rsgb_lf_group@blacksheep.org>
Verschickt: Fr, 7. Jul 2017 9:50
Betreff: LF: Simple coherent frequency generator

Hi Markus, Domenico, Stefan, LF

many thanks for last EbNaut decodes, dr Markus. And thanks Domenico
for your outstanding EbNaut automatic decoder!
In these days we have got good results using stand-alone NEO-M8N (or
NEO-7M as well) modules like reference frequency generator: (no more
external TCXO, OCXO, PLL,
etc....hi); obviously, the module with his patch antenna should be
installed in a good position. The output signal isn't affected by a
significant jitter (up to 1 MHz) and remains very stable in phase.


-A VERY SIMPLE COHERENT FREQUENCY GENERATOR (SCH1.JPG)-

We need only a buffer on TP5 (pin3 of the U-blox hybrid, connected
normally to the status LED) to adapt levels and impedance toward
amplifier.
SCH1.JPG is a simple solution tested by Tony IK1HGI, with GPS and
buffer installed outside the house. The square wave signal is applied
to PA using about 10 meters of RG174.
The solution with RS-232(TTL 3.3V)->WiFi converter is a practical
option (it works fine in my shack): you could use a normal COM (TTL
3.3V) to USB adapter.
Use "U-center" (by U-blox -
https://www.u-blox.com/en/product/u-center-windows) to pre-configure
the module.
After connecting it, it's necessary to set the navigation mode and
minimum elevation of sats (thanks to Domenico for the advice).

Go to...
- Menu - View
- Configuration view

- Select item "NAV5 (Navigation 5)" (left side)
- Set Dynamic Model to "Stationary" (right side)
- Set Min SV Elevation to 10 degrees
- Press Send button

- Select item "TP5 (Timepulse 5)" (left side).
- Select Frequency and Duty Cycle mode (right side)
- Set Duty cycle values (50% normally)
- Set QRG values Frequency and Frequency Locked; normal or x2 with
G0MRF PA (http://www.g0mrf.com/630m.htm) or x4 with a generic SDR
quadrature generator like
74HC74 (normally used with H-mode mixers)
- Press Send button

...obviously we need GPS module status ALWAYS in locked mode to obtain
a valid coherent signal...

- Select item "CFG (Configuration)" (left side)
- Select "Save current configuration" (right side)
- Select all Devices (in particular I2C-EEPROM) by keeping pressing Shift key
- Press Send button

Now the module is programmed.


-BPSK MODULATOR (SCH2.JPG)-

Now we need a BPSK modulator to send EbNaut messages: the simplest
method uses XOR (or XNOR) logic ports.
This is a very cheap, but fine solution to be EbNaut QRV in TX.
In particular, this modulator can be used succesfully on G0MRF class D
PA (http://www.g0mrf.com/630m.htm) and tested by Tony IK1HGI, but also
in any other amplifier.
In this last case, it needs a proper signal buffer.


All the best


73 de Riccardo IW4DXW