N6GN's L3 TNC Hardware Page
This page is for information related to the ongoing development of the RF
portion of the "Layer 3 TNC" radio/controller. The page is very much under
L3TNC RF Brief Description It may help to
look at the following block diagram while you read this.
L3TNC RF Block Diagram in .gif (poor quality, only
72 dpi) and in Postscript
and in Adobe .pdf
1265 MHz Mixer Layout(postscript)
are a microstrip 1265 MHz
IQ modulator (also known as an Image Reject or SSB Mixer).
This carrier oscillator Phase Noise plot
gives an idea of channel quality near the carrier. The oscillator in this
particular plot is not as good as can be done and the performance close to
the carrier could be much better with the addition of another integrator.
I had the plot handy though.
The I/Q Modulator output showing SSB Pilot Carrier
This is a plot which shows the USB pilot. The main carrier, at 1265 MHz,
and the LSB of the pilot are suppressed by the balance of the system. The
USB pilot is about 10 dB down from "full power". This is essentially the
despread spectrum of the information channel without any information present.
Most of the spectrum between the two pilot terms is available for transmitting
digital or analog information or both.
7 bit Direct Sequence Spreading Modulator showing the (unfiltered) 1240-1300
MHz Spectrum. In the final radio, the output to the
antenna will be preceeded by a linear phase bandpass filter to restrict output
to the main lobe which is entirely within the amateur band. Additionally,
I've tentatively positioned the carrier to "protect" the weak signal/moonbounce
part of the band at 1296.0 MHz. I'm hoping that the lower power and directional
antennas associated with using l3tnc as part of a network will allow full
coexistence with existing narrowband amateur services.
The top of screen is at the level of the unspread carrier so, combined with
a filter which can provide a few more dB, there would be perhaps 60 dB
suppression in the 1296 region. Combined with antenna directivities, this
will hopefully put any potential QRM below the noise floor of an EME or other
sensitive narrowband system.
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