Message-ID: <26D9EBB1476B467E9E02C10B3FACC2C8@PcMinto>
From: Minto Witteveen <minto.witteveen@gmail.com>
To: <rsgb_lf_group@blacksheep.org>
References: <4E3B1BFD.5090807@iup.uni-heidelberg.de> <4E3B2EA3.90003@iup.uni-heidelberg.de>
In-Reply-To: <4E3B2EA3.90003@iup.uni-heidelberg.de>
Date: Fri, 5 Aug 2011 23:59:36 +0200
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Subject: LF: Re: CW sked on 137 friday morning?
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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 isnât good enough, or if it is just insufficient 
S/N â 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 Yeasuâs 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 TVâs 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 FTâs S-meter is not very reliable, especially from 
S1-S9. But between S9 and S9+40 it is âreasonablyâ 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 didnât 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



--------------------------------------------------------------------------
Ceterum censeo Carthaginem delendam esse
-----Original Message----- 
From: Stefan SchĂ¤fer
Sent: Friday, August 05, 2011 01:43
To: rsgb_lf_group@blacksheep.org
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 SchĂ¤fer:
> 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