Re: [softrock40] RXTXv6.2 10m prototype tests
Thanks for the test results! I was seeing high IM distortion products
when I ran BPSK transmit in Rocky at 1 Watt output. Maybe the bias
current should be increased in the finals to permit operation at 1 Watt?
Also were you using a low phase noise crystal? Your MDS sensitivity
reading is much worse than what I was seeing in 500 Hz BW using
PowerSDR. I assume you are using the LT6231 op amp. I was using
crystals specified for low phase noise. Tony has ordered the same
crystals, except for the frequency, for use with the 10m RXTX kits he
Below is an e-mail with my measurements after your modifications and
upgrading to an LT6231 op amp: (BTW, for these measurements I was using
my crystal for 28.100 MHz center frequency. But the readings were the
same for my crystal for 28.200 MHz.)
"To: "Tony Parks" <raparks@...>
Sent: Saturday, November 17, 2007 12:25 AM
Subject: 10m RX LT6231 Mod
Before I started replacing the components I checked the MDS sensitivity
of the 10m RXTX. It was still about -100 -6 dBm or -106 dBm. After the
modifications with the low noise op amp the sensitivity was -114 -6 dBm
or -120 dBm with a 500 Hz bandwidth in CW mode with Power SDR at a
frequency of 28.107 MHz. I averaged a number of readings because even
with averaging turned on in PowerSDR the numbers jump around a lot.
Again the -6 dB comes from the fact I calibrated the output of the
signal generator into the scope 50 Ohm input at 0.317 Vpp. So this was
done the same way I did before as well.
However, I noticed the noise floor in Rocky still increases toward the
band edges (of the Rocky spectrum at 96 kHz sampling) even with the new
resistors and capacitors. (It was doing this as well with the old RC
combination and higher noise op amps.) It seems the noise floor is the
lowest near the center frequency. So I also tried it at 28.140 MHz,
about the maximum Alex has the default band limits set in Rocky to
prevent aliasing. The MDS degraded to -112 -6 dBm or -118 dBm.
So it looks like we gained 14 dB in sensitivity near the Rocky spectrum
center frequency for an MDS (S+N)/N = 3dB of -120 dBm in 500 Hz BW I
never did a test at the band edges with the original op amp and resistor
capacitor combinations, so it could be the MDS sensitivity at the band
edges could have been a couple dB worse with the old op amp as well. I
just don't know for sure. But in any case with the new
opamp/resistor/capacitor combination, the MDS at the band edge is now
> I just finished my 10m prototype of the RXRXv6.2. I ordered an
> overtone crystal of 112.160 MHz already last year. The daughter board
> works stable with the specified data of L100.
> The results of my first tests are uploaded to the files section:
> -> DJ9CS -> 'RXTXv6.2-10m-tests.pdf'.
> 73 Bodo, DJ9CS
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