[Skimmertalk] Skimmer and aggregator question(s)

Pete Smith N4ZR n4zr at contesting.com
Fri May 11 05:55:50 PDT 2012

Responses interleaved below, Kaz ...

73, Pete N4ZR
The World Contest Station Database, updated daily at www.conteststations.com
The Reverse Beacon Network at http://reversebeacon.net, blog at reversebeacon.blogspot.com,
spots at telnet.reversebeacon.net, port 7000 and
arcluster.reversebeacon.net, port 7000

On 5/10/2012 6:22 PM, kaz wrote:
> Hi folks.  First, apologies if this double posts to the list.
> Finally laid hands on a couple of softrock kits, and I am finally
> getting a chance to play with skimmer and SDR.  Way fun.  I expected the
> surface mount parts to be difficult when building the first Softrock.
> Never tried any surface mount project before.  Wrong.  Turns out reading
> the numbers to sort out the capacitors was the hard part. Bright lights
> and magnification, and even my 17yo son had trouble(and he has 20/13
> vision).
> But enough digression.
> Bought skimmer license, have skimmer running on 40m and 80m.  40m
> calibrated(I think), 80m still pending.
> Question#1
> I'm not clear on the relationship between the skimmers and aggregator.
> If I run a skimmer session for each softrock, do I run aggregator for
> each skimmer?
> My initial expectation was to run the skimmer sessions for each
> Softrock, use wintelnetx to put the spots together, and use aggregator
> to ship the spots to the RBN from the wintelnetx window/port used to
> collect the spots.
> I found the documents N4ZR has written to be "spot on", but I have not
> seen/found any that describe this relationship.  (I probably did not
> look hard enough....???..hints appreciated)

Yes, this approach is fine, in principle.  The thing that is important, 
from the RBN's perspective, is to keep the association between a given 
instance of CW Skimmer and the Softrock for a given band.  That way, if 
we see a calibration error coming up on the Skimmer Details page of the 
website <http.reversebeacon.net> you'll be able to associate it with 
that instance of Skimmer and make the necessary changes.

Rather than running WintelnetX, I suggest you do what Tim, KQ8M does.  
Here's a quote from an e-mail I just got from him.

"Every instance of skimmer has its own Aggregator. There is 3 instance 
of skimmer and Aggregator running on 2 computers. The other 2 computers 
have 2 instances. What I had learned from Dick, W3UA, was to rename each 
instance differently [he means to rename the exe file]and use separate 
directories, of course. You have to do that with Skimmer anyhow. I keep 
Aggregator in each skimmer's directories. Also, each skimmer uses the 
same callsign. If you use separate callsigns it comes out separately on 
the RBN."
> Question #2
> Is it necessary/required to open the port to the skimmer/aggregator to
> the world_wide_interwebz?  I would really rather not do that at this point.

Aggregator does not use a port, so you should be able just to start it 
and go.
> Other trivia:
> With two skimmers running on mostly dead bands, a dual core Pentium D
> (Dell Optiplex 745) ticks off about 15-20% CPU when the skimmers are
> minimized.  The 80m softrock skimmer is at 48khz on the on-boad
> Soundmax.  The 40m softrock skimmer is at 96khz on an ASUS Xonar DG.
> The Xonar DG seems to be a fantastic value for a sound card. Also
> available as PCI-E, Xonar DGX.  Its main limitation over the more
> expensive siblings in the Xonar line seems to be its 96khz max sample
> rate, vs 192khz for big brother.
96 KHz comes pretty cheap - the 192 KHz bandwidth is more of a specialty 

When you first crank up your Softrocks it is likely that you will have 
images on the opposite side of the center frequency from the real 
signals.  You need to run the I/Q Balance calibration to get rid of 
these.  That routine requires strong signals across the entire range, so 
I've found the easiest way is to turn my radio down very low (RF output) 
and provide the signals it needs from one end of the range to the other.

The other thing that helps a lot is to use audio isolation transformers 
on the two channels.  Without them you will probably see a fairly large 
noise bump at the center frequency, resulting from hum.  The iso 
transformers will "transform" this into a relatively narrow dead spot, 
caused by the lower frequency roll-off of the iso transformer.  I used 
some relatively good Triad isos in order no not have roll-off near the 
ends of the frequency range, but if you already have some my suggestion 
would be to try them and see.


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