Hello
Stefan,
I
have a question that is a digression from Tony’s question
but perhaps related:
Bill
(WB6BNQ), Graham and Wolf (on March 3, 2014) suggested
(thanks!) the following to make the narrow 1pps pulse from
my Trimble (Thunderbolt E) GPSDO] compatible with an
external USB sound card:
A
pulse stretcher based on either a modern version of 74123,
such as a 74HC123, or a stretcher made from half of a 74HC74
Dual D flip-flop [resistor from not-Q to not-R; parallel
speedup diode (anode to not-Q), and capacitor from not-R to
ground], to stretch the 1pps pulse to well over 10us (at
least a few milliseconds)
I
am preparing to interface two more Trimble Thunderbolt E
GPSDOs to an external USB sound card for SpecLab , for a VLF
loop-TX test this year (60 meter horizontal square loop with
6 kW PA power; low ERP but GPS disciplined so maybe some
interesting signals); and I wonder if the above solutions
(one-shot or flip-flop) for interfacing the narrow Trimble
1pps signal to an external USB sound card for SpecLab remain
the recommended approach. Do you have any thoughts on this?
Thank
you, and apologies if this obfuscates Tony’s thread.
73,
Jim
AA5BW
Hi Tony,
OK so if your RX and PC time is stable, we can give it a try.
-You need a stereo input soundcard and feed the PPS signal to
the right channel. Just run it at 48 kS/s. The PPS signal must
be DC decoupled and the level must be limited to 80% of the
ADC range, simply use 100nF and a resistive divider. The
values will depend on your GPS module and its output level.
-Download the latest version of SpecLab and install it to the
recommended folder.
-Turn the RX to 136.00000 kHz USB and use a 2.5 kHz wide SSB
filter. Connect the RX to the left channel of the soundcard
input.
-Download the usr file in this mail and open it into SpecLab
(File -> Load settings from...)
-Click on Components -> Show Components. A box opens. In
the top left corner, click on "SR cal". Another box opens. The
Status must be green, showing pps peaks OK. If the level is to
high, click on "scope" and see the peak form. Then you need to
adjust the divider of your GPS module to reduce or increase
the PPS level. The box must be green for most of the time in
the end. Click to scope again, there is a pulse counter PC and
an error counter EC. The error should be lower than 2 % or so,
for example PC=1000 EC=16. Just let it run a few hours and see
if the tracking is stable.
If you have problems in this step, tell us what the problem
is.
-Wait a few hours and check if text files appear at
C:\Spectrum\data After the first 40 minutes, a file should
appear each 10 minutes.
-Ask someone to transmit a short EbNaut message at 1s symbols
and make sure to record on this time.
So far. Then we can continue with part 3 :-)
73, Stefan
Am 23.10.2016 19:09, schrieb Tony Baldwin:
Hi Stefan
My receiver is an Elad FDM-DUO SDR with a 10 MHz GPS input.
Unfortunately SpecLab doesn't have that radio for an SDR
input, so I have to use the sound input via USB.
I could send the 1 PPS to my computer via RS 232 as well if
that helps.
73, Tony, EI8JK.
On 23/10/2016 17:51, DK7FC wrote:
Hi all,
I started to write the second part of this tutorial but when
finished i was not happy with the result.
The first thing one can say is that you will need a very
frequency stable receiver. There is no chance without an
external reference signal. For generating wav files using
SpecLab you will also have to use a ref signal to compensate
the drift of your soundcard. Some people have already
prepared things in the past. You can use a 1 PPS signal for
soundcard drift compensation or a down divided 10 MHz GPS
reference or a stereo soundcard receiving VLF MSK signals on
the other channel to compensate the drift.
Also the SpecLab configuration depends on your receiver
type.
Now i could simply make some assumptions what your equipment
may be but this may be not a good way.
So now i think it's better that we start with one example,
one (or more) of the stations who are interested in EbNaut
decodes on LF should describe the available system
components. Then we can
work it out what must be done.
We will need to have a stable RX frequency and a drift
compensated soundcard frequency in the end.
So who of those who are interested wants to start?
73, Stefan
