Hello Stefan,
I really cannot explain why I did not hear anything. But I will keep trying
, and improve receive conditions where possible. I did eliminate two QRM
generators, a Philips fluorescent lamp and an Alinco 30A switching power
supply (these are really horrible, they even have a knob to adjust the
‘noise offset’ i.e. adjust the switching frequency. This should have tipped
me off when I bought it…)
At this moment I only hear band noise and a lot of QRN cause by lightning in
Europe. The band noise is about +10 dB above the noise of the transverter
and receive, tested by switching off the Miniwhip so I don’t think that
sensitivity is the problem…
Currently I do not have the equipment to calibrate the s-meter of the Yaesu.
I will install and try Speclab to see if I can copy QRSS signals.
Just a question: How do you use speclab to measure the signal level of for
instance DCF39 AND the noisefloor.. By measuring both and comparing? - but
then I would have to disable the ALC of the FT817?.
I can try /p sometime, go out in the fields far away from man-made noise,
with the miniwhip, a 12 meter fiberglass pole, a 7Ah SLA, the transverter
and the 817.
Regards, Minto pa3bca
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Ceterum censeo Carthaginem delendam esse
-----Original Message-----
From: Stefan Schäfer
Sent: Saturday, August 06, 2011 16:51
To: [email protected]
Subject: Re: LF: Re: CW sked on 137 friday morning?
Hello Minto,
Am 05.08.2011 23:59, schrieb Minto Witteveen:
Stefan (et al),
I did listen this morning on 136.8 to see if I could copy you or any other
station, but the results were disappointing: I heard nothing.
Thanks for trying anyway.
Well, i was in QSO mit PA0A who must be close to you, so something must
be wrong...
I have an FT817 and an FT879 as possible receivers. Both are not known for
their superb receive quality but with a 5 pole filter + additional
amplification I got them to work quite reasonable on 500 KHz.
Both rigs are very bad on LF. Very insensitive and prone to heavy
intermodulation, especially at night.
So this weekend I build a quick-and-dirty 4 MHz uptransverter with a
SA612. The Yeasu’s are much more sensitive at these frequencies. To keep
strong LF and MF stations from causing intermodulation had to add 7-pole
Chebishev filter between a PA0RDT miniwhip and the transverter. For
details see:
http://www.pa3bca.nl/index.php?option=com_content&view=article&id=23&Itemid=17
Looks good, that page.
This morning (when there was almost no man-made QRM form TV’s etc) DCF39
was S9+30dB on the 897. On (4000+) 136.8 the noise was S 5 with the 2.4
KHz SSB filter, and S1 with the 500 Hz filter.
Now I know that the FT’s S-meter is not very reliable, especially from
S1-S9. But between S9 and S9+40 it is “reasonably” accurate.
If you use SpecLab for receiving, you directly get the signal level in
dB (i.e. dB below full scale of the ADC). Then you can measure the DCF39
level and the noise floor level. Meanwhile i am getting DCF39 at 80 dB
above noise in 488 mHz with the RX loop.
As far as I could find out DCF39 generates 50 KW ERP. If Stefan generates
0.5 Watt ERP (My guestimate)
Should be a few dB more ;-)
and the distance to my QTH is approximately the same, I would expect
Stefan to be 50 dB weaker. But 50 dB below DCF39 would still be above the
noise floor? So why didn’t I hear him (or for that matter, PA0A who is
closer and has 1 Watt ERP).
Maybe the S meter is worse than you think, maybe.
Before I finish my 1 kW TX I first have to make sure that I will be able
to copy any other station.... :-)
I had the same problems. But i immediately received DF6NM audible. So if
you don't even receive PA0A, there seems to be lack of sensitivity.
What happens with the noise floor if you disconnect the PA0RDT? How many
dB does the noise floor decrease?
Can you do /p tests?
Don't expect to much activity on LF. But there are new stations coming
on the band and you could be one of them and help making the band alie
again.
CU there :-)
73, Stefan/DK7FC
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