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.
I have no prior experience with 137 KHz so I have no idea if this is because
my receiver setup just isn’t good enough, or if it is just insufficient
S/N – the noise floor here is quit high on HF.
I am hoping for some insight from this esteemed mailing list..
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
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.
As far as I could find out DCF39 generates 50 KW ERP. If Stefan generates
0.5 Watt ERP (My guestimate) 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).
Before I finish my 1 kW TX I first have to make sure that I will be able to
copy any other station.... :-)
Regards, Minto pa3bca
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Ceterum censeo Carthaginem delendam esse
-----Original Message-----
From: Stefan Schäfer
Sent: Friday, August 05, 2011 01:43
To: [email protected]
Subject: Re: LF: CW sked on 137 friday morning?
Ah, forgot to mention the TX frequency: 136.8 kHz. I'm listening in a
250 Hz CW filter.
I'll call in QRSS too, maybe.
I cannot QSY my TX when using this UHF link...
73, Stefan
Am 05.08.2011 00:23, schrieb Stefan Schäfer:
LF,
I want to call for CW skeds now,i.e. for tomorrow morning.
After testing the UHF link today i was impressed by the silence of the LF
band when beeing in the forest with the loop! The band noise is about 15
dB above the soundcard noise now, which is OK for today but not for a
quiet winther sundday morning. BTW i built M0BMUs loop preamp and it works
excellent too! Still have to compare the homemade RX to the 706+preamp...
DCF39 peaked 80 dB S/N in 1.5 Hz. The sferics were much louder compared to
the background noise. Inbetween the sferics, CW reception would have been
possible. I even heared some short beeps, probably someone was testing
without hearing my call.
The UHF link works excellent! About 1 W RF power to a homemade 1/4 wave
wire on the car roof was totally enough to reliable key the PA. Even
normal CW is possible without problems. Just a few times the squelch
opened unwanted.
When installing a large RX loop in the trees, resonated and matched to 50
Ohm, i can make a tour with the bike and just the netbook and the homemade
RX (fed by the USB) and another 70cm mobile QRP TRX.
Tomorrow morning i want to do another test even farer away from the city,
about 5 km, where my earth antenna is placed. I'll take the single turn
loop again with me.
I hope to get a QSO partner then.
Will try to do something with the earth antenna as a RX antenna. A small
PI filter should match and band limit the whole thing... 800 to 50 Ohm.
Is someone QRV tomorrow? Ah, i think about 8...9 UTC... Other suggestions?
(no, no other hobby).
73, Stefan/DK7FC
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