GMSK Modulator Discontinuity

I have been playing around with the GRC (amazing tool - really love
it!) and I was just taking a look at the GMSK Modulator with some
random data.

I couldn’t get the random data block to work properly, so I used a
file source that is just some ascii text. I didn’t think this would
matter since it’s just random data anyway. I have it set to repeat
the data once done.

I notice there is a discontinuity with the GMSK modulator. I am not
sure where it’s coming from, or if it’s in the Constellation Sink, but
I thought I would just bring it up to the list.

I have attached the sample.grc.xml file along with the samples.txt
ascii file I made. The concern is when the Constellation Sink format
is set to “line”.

I have also attached a picture of the discontinuity I am seeing.

Brian

[ My first post, new to radio ]

I saw on the list the suggestion that the PCR1-100 could make a good
frontend for the USRP. Well, what the heck, 75$ is not much. The radio
works just fine with its windows software, and I can get basic control
of it via hamlib. I searched the net for PCR-100 hacking and found a
couple of links. The first is to get the discriminator output at pin8 of
IC 10. No problem, and the second link refers to a DRM mixer. The photos
are unclear, but I assume it taps the 10.7Mhz IF. Does anyone have any
information on tapping the 10.7Mhz IF on this thing, or am I barking up
the wrong tree for using this as frontend to the usrp ?

Many thanks,
Simon Convey

I tried it with the samples.txt and the random source doing 1’s and 0’s.
The constellation doesnt seem to be showing a discontinuity. I attached
the screenshot. Maybe this is a bug in the newer version of the GMSK
code? I am running whatever I checked out of the release branch a month
ago. -Josh

I just bought one of these as well. Right now there is a guy on eBay
selling a load of them (with no accessories) for $50 each plus $5
shipping. Here is the only mod info that I’ve found on the 10.7 MHz
IF:

The buffered 10.7 MHz IF Output is available at the emitter of
transistor of Q85. Q85 is located close to the edge of the large board,
near J1. If you place the radio with the antenna connection to the left,
Q85 is the first transistor to the right of the smaller IF filter at the
top left hand corner of the RF board. This is directly above the metal
can for one of the LO’s. The emitter is the upper left terminal (if the
radio is oriented as described above). There will be a DC level at this
point, so will want a coupling capacitor.

I have a PCR-1000 (similar to PCR-100). Where can I
find the instructions to tap the 10.7 Mhz IF for this
receiver? The Data Jack output is the FM
Discriminator which is not as good as the 10.7 Mhz IF.

Also, once you tap the 10.7 Mhz IF, where does it
connect on the Basic RX board? If it connects using
the SMA connector, what is the method to solder the
wires from the 10.7 Mhz IF to the SMA cable?

Thanks,

— Jim P. [email protected] wrote:

of the large board,
point, so will want a coupling capacitor.

works just fine with its windows software, and I
thing, or am I barking up
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George B.
[email protected]

On 2/12/07, Josh B. [email protected] wrote:

I tried it with the samples.txt and the random source doing 1’s and 0’s.
The constellation doesnt seem to be showing a discontinuity. I attached
the screenshot. Maybe this is a bug in the newer version of the GMSK
code? I am running whatever I checked out of the release branch a month
ago. -Josh

Very interesting. I am running on Cygwin, and I am using the 3.0.2
release tarball from the website, not any SVN checkout.

I’ll try to investigate this further on my end.

Thanks,
Brian

I found it at:
http://www.wentztech.com/radio/PCR1000/PCR1000.html

I found the link at one of the PCR-1000 Yahoo Group
sites.

This one has very nice close up pictures.

I am not an electronics person, but the procedure mod
looks like you have to solder a capacitor between the
Q85 point and the coax cable which leads to your
external antenna, correct? And the coax foil
shielding is connected to the PCR-1000 ground screws.

Can someone determine if these same mods also work for
the PCR-100?

Thanks,

— George B. [email protected] wrote:

wires from the 10.7 Mhz IF to the SMA cable?

each plus $5
connection to the left,

works just fine with its windows software, and I
Does anyone have any


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[email protected]

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George B.
[email protected]

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