Message-ID: <4E3E614D.3060409@iup.uni-heidelberg.de>
Date: Sun, 07 Aug 2011 11:56:29 +0200
From: =?UTF-8?B?U3RlZmFuIFNjaMOkZmVy?= <schaefer@iup.uni-heidelberg.de>
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; de; rv:1.9.1.11) Gecko/20100711 Thunderbird/3.0.6
MIME-Version: 1.0
To: rsgb_lf_group@blacksheep.org
References: <4E3B1BFD.5090807@iup.uni-heidelberg.de> <4E3B2EA3.90003@iup.uni-heidelberg.de> <26D9EBB1476B467E9E02C10B3FACC2C8@PcMinto> <4E3D54DE.1000202@iup.uni-heidelberg.de> <5D042DA2B0C04AA09C5416113128574C@PcMinto>
In-Reply-To: <5D042DA2B0C04AA09C5416113128574C@PcMinto>
Subject: Re: LF: Re: CW sked on 137 friday morning?
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: quoted-printable
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
X-AOL-SCOLL-URL_COUNT: 0  
x-aol-sid: 3039ac1d41094e3e616c05ee
X-AOL-IP: 195.171.43.25
X-AOL-SPF: domain : blacksheep.org SPF : none


Hello Minto,

Am 07.08.2011 00:10, schrieb Minto Witteveen:
> Just a question: How do you use speclab to measure the signal level of=20
> for instance DCF39 AND the noisefloor.. By measuring both and comparing=
?
I don't use a commercial HF TRX for LF but a down-converter (LF-125 kHz)=20
so i am not limited to a SSB filter bandwidth. I can display 125...149=20
kHz when running the soundcard at 48 kS/s. So a slight difference here.
But generally you must switch off the AGC and ALC and noise blanking and=20
all that affects the output AF level. Then you can measure the absolute=20
levels, e.g. -10 dB for DCF and -80 dB for the band noise and -90 dB for=20
the RX noise.
Just read it out on the right side.
I did a audio recording during the QSOs. My loop was beaming N/S, so not=20
optimally for DCF-39. Anyway it was 85 dB S/N in 488 mHz (i use 488 mHz=20
for QRSS-3). So this is an example how to simply read out the SNR:=20
http://dl.dropbox.com/u/19882028/LF/DCF39%20in%20488%20mHz.png
Anyway there could be 10 dB more sensitivity on my RX to have best=20
reception in a quiet sunday morning in winther...

> - but then I would have to disable the ALC of the FT817?.
Not sure but i would disable anything ;-)
> I can try /p sometime, go out in the fields far away from man-made=20
> noise, with the miniwhip, a 12 meter fiberglass pole, a 7Ah SLA, the=20
> transverter and the 817.
If you are outside in a flat field, you maybe do not need to lift the=20
antenna to 12m! 3m could be reasonable. Yes, beeing outside will at=20
least show you if its all caused by local QRM...

73, Stefan/DK7FC


>
> Regards, Minto pa3bca
>
>
>
>
> -----------------------------------------------------------------------=
---=20
>
> Ceterum censeo Carthaginem delendam esse
> -----Original Message----- From: Stefan Sch=C3=A4fer
> Sent: Saturday, August 06, 2011 16:51
> To: rsgb_lf_group@blacksheep.org
> 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=20
>> 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=20
>> known for their superb receive quality but with a 5 pole filter +=20
>> additional amplification I got them to work quite reasonable on 500 KH=
z.
>> Both rigs are very bad on LF. Very insensitive and prone to heavy=20
>> intermodulation, especially at night.
>> So this weekend I build a quick-and-dirty 4 MHz uptransverter with a=20
>> SA612. The Yeasu=E2=80=99s are much more sensitive at these frequencie=
s. To=20
>> keep strong LF and MF stations from causing intermodulation had to=20
>> add 7-pole Chebishev filter between a PA0RDT miniwhip and the=20
>> transverter. For details see:
>> http://www.pa3bca.nl/index.php?option=3Dcom_content&view=3Darticle&id=3D=
23&Itemid=3D17=20
>>
> Looks good, that page.
>> This morning (when there was almost no man-made QRM form TV=E2=80=99s =
etc)=20
>> DCF39 was S9+30dB on the 897. On (4000+) 136.8 the noise was S 5 with=20
>> the 2.4 KHz SSB filter, and S1 with the 500 Hz filter.
>> Now I know that the FT=E2=80=99s S-meter is not very reliable, especia=
lly=20
>> from S1-S9. But between S9 and S9+40 it is =E2=80=9Creasonably=E2=80=9D=
 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 DCF3=
9
> 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=20
>> 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=20
>> Stefan to be 50 dB weaker. But 50 dB below DCF39 would still be above=20
>> the noise floor? So why didn=E2=80=99t I hear him (or for that matter,=
 PA0A=20
>> 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=20
>> able to copy any other station.... :-)
> I had the same problems. But i immediately received DF6NM audible. So i=
f
> 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 man=
y
> 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