THE GRE GINA
A PRODUCT REVIEW
The GRE GINA series of 915 MHz SS radios has been on the market a couple of years now.
These workhorse, inexpensive radios provide solid performance at medium data rates for
a variety of LAN/WAN or industrial applications. Available as a "Dumb" radio
in the GINA 5000 or with a builtin 80C188 microprocessor in the GINA 6000, these
radios possess all the basic features needed for many serious applications.
With a sensitive (<-100 dBm sync threshold) receiver and a 1 watt transmitter, the
two GINAs are very capable, long range LAN/WAN transceivers. RF/SS owns two GINA 6000s
that we use for wireless demonstrations and as loaners for customer evaluation and one
GINA 5000. We use the GINA 5000 for benchtop SS signal generator duty as well as for
general purpose SS testing. This review will deal with results we obtained on the GINA 5000.
The unit we tested had a power output of 1.04 Watts (+30.17 dBm) on our HP435A power
meter at 12 VDC input. The radio draws 433 milliamperes on receive and about 793
milliamperes on transmit. It does get a little warm after half an hour or so of
continuous transmit -- but how many other SS radios out there can even transmit continuously?
The output spectrum was observed on our HP8561A 1 kHz to 6.5 Ghz spectrum analyzer.
Figure 1, below shows a 500 Mhz wide span around the main 915 MHz output from the
GINA 5000. Here the detector mode was normal and the display was 10 dB per division.
Resolution bandwidth was 2 Mhz, so fairly reliable peak power measurements are possible.
We fed the output of the GINA to a 20 dB Narda directional coupler and then a 10 dB
pad to the spectrum analyzer. The calibrates loss ahead of the analyzer was 31.2 dB.
Note in figure 1 that two spurs are present in the output spectrum at + and -
eighty-something Mhz from the GINA's main output. These spurs are -45 to -48 dBc
and are due leakage of the transmit IF in the output. Otherwise the output
spectrum of this radio looks very good, in a wide span.
Figure 2 below shows the output spectrum in a 25 MHz wide sweep using the positive
peak detector mode of the analyzer. The [ sin(x) ] /(x) nature of the direct
sequence (DS) SS signal is becoming apparent in this plot.
Figure 3, at right, makes the DS spectrum even clearer. Again the positive peak
detector mode was used in this plot. In this plot, the span width is only 10 MHz
and the PN clock nulls at + and - 2 Mhz are very clear. The chip rate used in
this mode of the radio was 2 Mhz. Note that the fist sidelobes are approximately
13 or 14 dB down from the peak of the output spectrum. Thus GRE uses very little
narrow band RF filtering to archive spectral roll off. The -20 dB (99%) BW of
the output spectrum is 7 MHz. Thus the radio should not be operated closer than
about 3.5 MHz from a band edge to ensure FCC compliance with band edge spurious limits.
Figure 4, below, shows a narrow band, 500 kHz span plot of the carrier and
the PN spectral lines that are visible in a 3 kHz RBW. The carrier is suppressed,
as shown in this plot, about 18 dB below the peak output level. The peak level
of the discrete PN spectral lines appears to be 22 or 23 dB below peak output,
in this plot. Remember that the FCC requires these lines to be at least 22
dB below the one Watt power level in Paragraph 15.247. To verify compliance,
we took a final measurement. This showed that the discrete + and - 16 kHz lines
are at least 6 dB below the carrier level and are fully compliant! Note that
figure 4 was taken while averaging over 16 separate sweeps. This averaging
reduces video noise and makes for a clearer display.
From these plots it can be seen that GRE uses a 127 bit (seven shift register
maximal length shift register sequence PN generator) long PN code. I'm almost
certain that GRE uses the feedback taps that make the GINA 5000 legal under
amateur radio part 97 rueles. Thus you could use a GINA 5000 at up to 1500 watts
PEP output, with an outboard power amp, if you used it in amateur radio service.
The GINA used for these tests was set up for asynchronous data communication at
a data rate of 9600 Baud, in half duplex mode. The GINA is a fine, reliable
workhorse -- try one!
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