Due to interferences we deinstalled the TX and made some RF-measurements on Saturday, 13th of November at the QTH of Richard (DF5SL) in Stuttgart-Büsnau.
On the pictures below you will see the results with some explanations...
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POCSAG-TX of DB0LX:
- Kenwood TR-8300 (below) - Modulator and Filterstage (up) |
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In the Lab of DF5SL:
(f.l.t.r.: DL3SDW, DF5SL) |
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TR8300 connected to Laptop sending the modulating signal |
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picture above zoomed....
on the left and right of the carrier you can see some spectral-lines making interferences. |
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we found out that on the modulation-line (output of mod-filter -> Varicaps) there was RF on the modulationsignal |
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after installation of a 1nF blocking-cap from the hot modulationline to GND the signal was free of any RF |
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picture above zoomed...
You can see fine the results of the filter decreasing the rise/fall-time of the raw rectangular signal out of the Laptop. |
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outputsignal still the same :-( |
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lines on the left and right of the main carrier is the local-oscillator |
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same picture like above with less viewable grid but better beam-intensity. |
We did not tried too much for improving the output signal
- because the whole TX-concept is old fashioned and there might be more
work getting it up-to-date than making a complete new TX.
So as you can see out of the results above, we are thinking
of installing a new modern TX for POCSAG-Transmissions at our club home.
last
update: 14.11.99
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