[CQ-Contest] Summarizing the Skimmer Accuracy Thread

[Pete Smith N4ZR]

Bret, I am a little puzzled by your complaint. When you refer to 
"wrong-frequency spots" are you referring to spots that vary by 0.1-0.2 
KHz, or to imagesequidistant from the center frequency of a given 
receiver? If the former, you should be aware that each receiver on the 
RBN is separately calibrated, and we notify the operators any time we 
see spots that are more than that amount off one of a number of 
reference stations.

It is true that I/Q receivers feeding sound cards for digitization are 
prone to images spaced equidistant from the center frequency, but this 
is not generally true with direct down-conversion designs such as the 
QS1R.  We had a couple of exceptions during ARRL CW, and we are trying 
to understand what made them different from the other 70 or so identical 
receivers that did not have the problem.

73, Pete N4ZR
Check out the Reverse Beacon Network at
http://reversebeacon.net,
blog at reversebeacon.blogspot.com.
For spots, please go to your favorite
ARC V6 or VE7CC DX cluster node.

On 2/24/2013 8:59 PM, VR2BrettGraham wrote:
> S56A added:
>
>> VR2BG/p wrote: How many wrong frequency spots are there on RBN?
>>
>> I had short 10 minutes CQ run in ON UBA CW contest this morning with 
>> 100 W
>> and tribander on 14025,75 kHz.
>>
>> RBN had 3 spots on 14025,7 kHz, 31 spot on 14025,8 kHz and 10 spots on
>> 14025,9 kHz. No bad spots.
>>
>> They all fit within my sharp 250 Hz CW filter on third 455 kHz IF. No 
>> sweat
>> apart from occassional zero beat.
>
> No wrong-freq RBN spots of me from XV when I was there last summer, 
> Marijan - but I was barefoot too & far enough away from all the 
> skimmers for any of the mechanisms behind the wrong-freq spots to 
> manifest themselves, IMHO.
>
> Instead, take ALL the RBN spots for an entire day & then look for same 
> call (not just your own) spotted at exactly the same time on either a 
> different band or frequency (say >1 kc away) from any other spot of 
> the same call.
>
> I need to correct my previous post - when looking for spots NOT at 
> exactly the same time, you will find one wrong-freq spot matches up 
> with multiple correct-freq spots.  If you look for spots at EXACTLY 
> the same time, they tend come in pairs (a correct one matches up with 
> the wrong one; also wrong one matches up with the correct one), so 
> total number of wrong-freq spots can be found by dividing by two.  To 
> get a feel for how bad it is in a more realistic 
> within-a-minute-or-two-of-each-other (or possibly where call is same 
> other than one character) is beyond my ability with this new-fangled 
> database stuff.
>
> It could be that during the five minute period I found on 2012-03-08 
> where UA9CDC was spotted on three different bands, Igor was really 
> there.  Or maybe he had one of those fecal signals he mentioned in his 
> post... though there is a mechanism responsible for 
> same-or-close-kc-but-different-Mc RBN spots.
>
> Though every non-weekend day I've looked at RBN data I see all the 
> various wrong-freq spots & if there was a way to get a feel for how 
> many they were & that were added to all the busted call spots, I 
> believe the total is more significant than the techno-crowd would like 
> to admit.
>
> 73, ex-VR2BG/p.
>
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