Message-ID: <4E7BEAB2.4010205@telus.net>
Date: Thu, 22 Sep 2011 19:10:58 -0700
From: Scott Tilley <sthed475@telus.net>
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To: rsgb_lf_group@blacksheep.org
References: <4E7BB876.2080607@telus.net> <4E7BDC97.5040808@iup.uni-heidelberg.de>
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Subject: Re: LF: VE7TIL long integration grabber online...
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Hi Stefan

In the past three years since I began prolonged 'low noise' listening 
November has traditionally been the beginning of good opportunities for 
EU/VE7 DX.  However,  DCF39 has surprised me this year with decent 
showings already!  A couple of nights ago it reached audible levels!

This isn't a new effort, G3PLX and I worked on a similar study about 6 
years ago but I and he where limited by noise and a small TX antenna in 
my case and him by a limited LF RX system.

I'd tweek out that system of yours and be ready to lobe some RF over 
this way as I have a feeling that we may get some good opportunities 
this season...  Timing is key...!  You need to be ahead of the curve here.

My personal goal is to see if it is possible to detect an amateur EU 
station in VE7.  I have no concerns about the usability of the signal 
until we demonstrate that its even possible.

As a suggestion on how to get QRO with 100% keydown, consider using many 
smaller stages combined to produce lots of power rather than one stage 
pushed to the edge of meltdown.  This strategy reduces the need to 
stress a single stage when pushing everything you can out of it.  My 
MOALFA is capable of 2KW keydown all night long and uses 4 stages 
combined into one output.  I use a lumped four port Wilkinson Combiner.  
As an added 'bonus'  you get 'free' output filtering without the need 
for more components (and loses).  Jay, W1VD has a similar design in 
which he uses a transformer arrangement to do the combining which allows 
him to use it on 600m but does require additional output filtering for 
each band, a classic engineering compromise!

With my combined stage amp the only time I lost a transistor was when I 
melted the dummy  load during qualification testing years ago...  Since 
then I've logged hundreds of hours on the same transistors.

I believe the DECCA TX also uses a combiner approach to achieve high 
reliability at QRO.

Another advantage is you can build a couple of identical transmitters 
and separate them for other tasks etc.  VE7SL and I did this during one 
of our first ZL attempts years back.

Just make sure you use one LO path and only ONE digital division device 
to drive the driver ICs.  The reason for only one digital division 
device is based on the fact a Type D flip flop (or otherwise) can start 
in any one of four phases on power up.  If you have two as in the case 
of a two complete TX combiner situation you'll need to reset the power 
on one until it matches the other...

GL over there!

73 Scott






On 9/22/2011 6:10 PM, Stefan Schäfer wrote:
> Hi Scott,
>
> A "6000" grabber on LF. I never thought that this will come truth ;-)
> Well, to leave a trace there i should TX at least 1 hour key down. 
> Currently DCF39 rather shows poor levels and i have to optimise my 
> variometer, so it will take some time until i'll try. But i'm watching 
> your DCF plot and will think about it. Actually the system can stand 
> such a veeery slow transmission but i don't want to leave it 
> unattended for that first test...
>
> You said November is about the best month for DL_VE7 ?
>
> 73, Stefan/DK7FC
>
> Am 23.09.2011 00:36, schrieb Scott Tilley:
>> Hi All
>>
>> I've completed the preliminary configuration of the long integration 
>> grabber.
>>
>> Presently it can be found by clicking on the 'grabber 1' button of my 
>> website and looking under the main grabber window.
>>
>> It's running with a 424 uHz FFT bin width. Each pixel takes 600 
>> seconds...  You'll want to ensure you have a nice soft seat to be 
>> sitting on the edge of to watch this grabber :-)
>>
>> Center QRGs are presently:
>> 136170 +/- 0.2Hz
>> 137780 +/- 0.2Hz
>>
>> Please advise if QRGs need adjustment to coordinate with 
>> international activity.
>>
>> Comments welcome.
>>
>> 73 es gl
>>
>> Scott
>> VE7TIL CN89dk
>> http://www3.telus.net/sthed/argo/
>
>