Jim, LF,
Thanks for running the tests. Interesting results. Much slower QSB than
I expected.
I found no improvement using a tuned pre-amp, so left it out of circuit
from about 2300.
I've just done some MDS tests on my R75 using various combinations of
external and internal pre-amp. It appears that the external tuned
preamp is of about the same MDS improvement as the internal "pre amp 1"
setting - the MDS is then (feeding in via a few antenna switches and a
h/b 500kHz LPF) -129dBm. The R75 with no pre-amplification measures
-124dBm. The R75 internal "preamp 2" improves the MDS to -133dBm, but at
the expense of perhaps linearity problems.
IPO MDS = -124dBm
IP1 MDS = -128dBm
IP2 MDS = -133dBm
IPO + external tuned pre-amp MDS = -129dBm
I suppose the tuned pre-amp might be beneficial at reducing the
amplitude of any intefering strong carriers, so in the real world it
may be worthwhile.
I'll leave the WSPR running in RX mode today, on the off chance that
someone else might have a go during daylight hours. Dial freq. 136.000,
USB mode with a 250Hz IF filter, centred on 1500Hz (137.500 carrier)
Cheers,
John
On Wed, 14 Jan 2009 00:21:30 -0000
"James Moritz" <[email protected]> wrote:
> Dear LF Group,
>
> Thanks for all the reports - The M0BMU WSPR beacon is still running,
> and will probably QRT at around 0100utc.
>
> So far the reports this evening have been from (in no particular
> order) F1AFJ, GM4SLV, DF6NM, DL4YHF, F5WK, LA9BEA, F4DTL, DK6NI,
> G4FDD, F4EMV, I2PHD, G3WCB and IK1ODO. Many thanks to all - It is
> good to see some calls who are not previously "known" on LF.
>
> I would be interested to try another 136k WSPR session during
> daylight - bearing in mind the long ground wave range on 136k, and
> the relatively low QRN during the day, I think results could be good.
> Perhaps this weekend.
>
> John - your lack of trees is not such a bad thing on 136k, where they
> soak up a lot of your TX power. In the experiments I did about a year
> ago, I found that an inv L antenna that was nearly identical to the
> antenna I am using now except that it was in the middle of a field,
> was 24 times as efficient as my home antenna, which is surrounded by
> assorted trees and buildings ( it was 6 times more efficient on
> 500k). So you might not need a tall antenna to get a reasonable
> signal in your treeless landscape. True, I am also using quite high
> power, but then looking at the SNR figures on your spots, there is
> about 10 - 20dB margin over the minimum possible SNR for decoding. so
> you could probably get away with less power too.
>
> Cheers, Jim Moritz
> 73 de M0BMU
>
>
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