Topband: Skimmer calibration
ALL I have tested RBN / skimmer raw data and Excel with preprocessing with CSVed to confirm station performance after many major CW contests I have been in. In order to see how a station covers a certain target area, I typically take one hour timeslots, one country or in the case us US, one zone to select the RBN listeners and then calculate the averages and variance of RBN measurements. Typically you I try to find some 50-100 measurements / TX station / hour for comparisons. In The outcome is averages varying between 10 to 30 dB and a variance of about 10 dB which is really quite a big number. This variance contains all the differences between RBN listerner station antennas, propagation, QSB etc., however the general grouping of stations to high performance (OH8X, OH2BH, OH4A), good and normal holds quite well if you know what antennas stations have at this end. A high stack is a high stack, always. Although it has been tempting to do, to me it seems to be statistically impossible to confirm much smaller than 3-5 dB difference between stations using this method. This is if you know the variance, number of measurements and the difference between averages of measurements and perform a student's p-test to confirm if the averages are really different or not. The rough groupings hold really well though, difference between normal and high performance stations holds. And I can see where my own signal sits in these groupings. MarkkuWW1C/OG2A/OH2RA _ Topband Reflector Archives - http://www.contesting.com/_topband
Topband: Skimmer calibration
Hello Mike You forget that on this side of the pond, the majority of us live on pocket handkerchief sized plots. :-) The representative of a major building company in the UK was on TV yesterday saying that 1000 sq ft was plenty big enough for a three bedroomed house. I imagine that would be the area of one room in a lot of houses in the USA. Even a K9AY needs a 30ft by 30ft space with a central support and a lot of new builds here don't even have gardens that size. You've only got to look at the population densities to begin to see the problem Population density (people per sq. km of land area) USA - 35 UK- 265 Netherlands - 498 France - 121 Germany - 231 Italy - 203 We'd all love to have the space to put up phased arrays or Beverages and even a Flag, K9AY, EWE, is out of the question for a large number of us. And as for quiet locations well for the vast majority of us those again are a thing of the past unless you go out portable. Switched mode power supplies and cheap plasma TVs etc have seen to that. Nothing comes with a good old linear power supply nowadays and any power supply coming out of the Far East has got to be suspect 73s Tracey G5VU On Tue, Aug 19, 2014 at 5:33 AM, Mike Waters mikew...@gmail.com wrote: When I last investigated, all the skimmers and Web SDRs that were outside of North America all had terrible receive antennas for copying DX signals on 160. (And who knows how many of them are in quiet locations?) When I say terrible, I mean small magnetic loops, very short whips, low dipoles, a random end-fed wire, etc. No phased arrays or Beverages, and not even a Flag, K9AY, EWE, etc. Does anyone know if that is still the case? 73, Mike www.w0btu.com _ _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Skimmer calibration
Iceland: three people per square km - Original Message - From: Tracey Gardner lt;tracey.gard...@talktalk.netgt; To: topband@contesting.com Sent: Wed, 20 Aug 2014 02:30:49 -0400 (EDT) Subject: Topband: Skimmer calibration Hello Mike You forget that on this side of the pond, the majority of us live on pocket handkerchief sized plots. :-) The representative of a major building company in the UK was on TV yesterday saying that 1000 sq ft was plenty big enough for a three bedroomed house. I imagine that would be the area of one room in a lot of houses in the USA. Even a K9AY needs a 30ft by 30ft space with a central support and a lot of new builds here don't even have gardens that size. You've only got to look at the population densities to begin to see the problem Population density (people per sq. km of land area) USA - 35 UK- 265 Netherlands - 498 France - 121 Germany - 231 Italy - 203 We'd all love to have the space to put up phased arrays or Beverages and even a Flag, K9AY, EWE, is out of the question for a large number of us. And as for quiet locations well for the vast majority of us those again are a thing of the past unless you go out portable. Switched mode power supplies and cheap plasma TVs etc have seen to that. Nothing comes with a good old linear power supply nowadays and any power supply coming out of the Far East has got to be suspect 73s Tracey G5VU On Tue, Aug 19, 2014 at 5:33 AM, Mike Waters lt;mikew...@gmail.comgt; wrote: gt; When I last investigated, all the skimmers and Web SDRs that were outside gt; of North America all had terrible receive antennas for copying DX signals gt; on 160. (And who knows how many of them are in quiet locations?) gt; gt; When I say terrible, I mean small magnetic loops, very short whips, gt; low dipoles, a random end-fed wire, etc. No phased arrays or Beverages, gt; and not even a Flag, K9AY, EWE, etc. gt; gt; Does anyone know if that is still the case? gt; gt; 73, Mike gt; www.w0btu.com gt; _ gt; _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Skimmer calibration
Iceland: three people per square km. :) - Original Message - From: Tracey Gardner lt;tracey.gard...@talktalk.netgt; To: topband@contesting.com Sent: Wed, 20 Aug 2014 02:30:49 -0400 (EDT) Subject: Topband: Skimmer calibration Hello Mike You forget that on this side of the pond, the majority of us live on pocket handkerchief sized plots. :-) The representative of a major building company in the UK was on TV yesterday saying that 1000 sq ft was plenty big enough for a three bedroomed house. I imagine that would be the area of one room in a lot of houses in the USA. Even a K9AY needs a 30ft by 30ft space with a central support and a lot of new builds here don't even have gardens that size. You've only got to look at the population densities to begin to see the problem Population density (people per sq. km of land area) USA - 35 UK- 265 Netherlands - 498 France - 121 Germany - 231 Italy - 203 We'd all love to have the space to put up phased arrays or Beverages and even a Flag, K9AY, EWE, is out of the question for a large number of us. And as for quiet locations well for the vast majority of us those again are a thing of the past unless you go out portable. Switched mode power supplies and cheap plasma TVs etc have seen to that. Nothing comes with a good old linear power supply nowadays and any power supply coming out of the Far East has got to be suspect 73s Tracey G5VU On Tue, Aug 19, 2014 at 5:33 AM, Mike Waters lt;mikew...@gmail.comgt; wrote: gt; When I last investigated, all the skimmers and Web SDRs that were outside gt; of North America all had terrible receive antennas for copying DX signals gt; on 160. (And who knows how many of them are in quiet locations?) gt; gt; When I say terrible, I mean small magnetic loops, very short whips, gt; low dipoles, a random end-fed wire, etc. No phased arrays or Beverages, gt; and not even a Flag, K9AY, EWE, etc. gt; gt; Does anyone know if that is still the case? gt; gt; 73, Mike gt; www.w0btu.com gt; _ gt; _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Skimmer calibration
- Original Message - From: Tom W8JI w...@w8ji.com To: topband topband@contesting.com Sent: Tuesday, August 19, 2014 10:08 PM Subject: Re: Topband: Skimmer calibration BC antennas have the elaborate radial system in order to get that groundwave while the typical on ground ham vertical loses a lot of the 0-10 degree (or more) radiation. Go to the beach to get it back.or go with elevated radials. That just isn't factual at all. Radials under the vertical antenna have virtually no effect on wave angle unless they are sparse and grossly unbalanced, allowing them to radiate like a low horizontal antenna. Radials change the efficiency, not the pattern, unless the radials radiate like a dipole. 73 Tom Note that I didnt say anything about changing the pattern, just the energy included at low angles and where the efficiency starts at the base and at the often poorly understood Fresnel Zone if you really want more power in those low angles and not heating worms or sand granules. Carl KM1H _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Skimmer calibration
I said: That just isn't factual at all. Radials under the vertical antenna have virtually no effect on wave angle unless they are sparse and grossly unbalanced, allowing them to radiate like a low horizontal antenna. Radials change the efficiency, not the pattern, unless the radials radiate like a dipole. 73 Tom Note that I didnt say anything about changing the pattern, just the energy included at low angles and where the efficiency starts at the base and at the often poorly understood Fresnel Zone if you really want more power in those low angles and not heating worms or sand granules. That, by definition, is a pattern change. You said it improves groundwave. What you think happen just does not happen. It improves efficiency. It does not change elevation pattern, it does not change Fresnel zone losses significantly. It does not improve groundwave any significant amount more than it changes sky wave. This is because the often poorly understood Fresnel zone extends far beyond practical radial field area, and virtually all of the ground wave attenuation from soil losses is miles from the antenna over the entire long length of a path. It is not localized loss. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Skimmer calibration
I said: That just isn't factual at all. Radials under the vertical antenna have virtually no effect on wave angle unless they are sparse and grossly unbalanced, allowing them to radiate like a low horizontal antenna. Radials change the efficiency, not the pattern, unless the radials radiate like a dipole. 73 Tom Note that I didnt say anything about changing the pattern, just the energy included at low angles and where the efficiency starts at the base and at the often poorly understood Fresnel Zone if you really want more power in those low angles and not heating worms or sand granules. That, by definition, is a pattern change. You said it improves groundwave. What you think happen just does not happen. It improves efficiency. It does not change elevation pattern, it does not change Fresnel zone losses significantly. It does not improve groundwave any significant amount more than it changes sky wave. This is because the often poorly understood Fresnel zone extends far beyond practical radial field area, and virtually all of the ground wave attenuation from soil losses is miles from the antenna over the entire long length of a path. It is not localized loss. 73 Tom All of which is well known and well published. You might ask Frank, W3LPL, or Richard Fry to explain it to you better than I seem to do since you appear to get hung up on the semantics. Looking at the coastal AM BCB patterns I mentioned a week (WGBB 1240) ago or others recently will show you the effects of salt water and land. Carl KM1H _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Skimmer calibration
On Tue,8/19/2014 7:08 PM, Tom W8JI wrote: Radials under the vertical antenna have virtually no effect on wave angle unless they are sparse and grossly unbalanced, allowing them to radiate like a low horizontal antenna. Radials change the efficiency, not the pattern, unless the radials radiate like a dipole. On Wed,8/20/2014 9:05 AM, Tom W8JI wrote: This is because the often poorly understood Fresnel zone extends far beyond practical radial field area, and virtually all of the ground wave attenuation from soil losses is miles from the antenna over the entire long length of a path. It is not localized loss. I agree completely with both of Tom's posts. 73, Jim K9YC _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Skimmer calibration
- Original Message - From: Jim Brown j...@audiosystemsgroup.com To: topband@contesting.com Sent: Wednesday, August 20, 2014 12:48 PM Subject: Re: Topband: Skimmer calibration On Tue,8/19/2014 7:08 PM, Tom W8JI wrote: Radials under the vertical antenna have virtually no effect on wave angle unless they are sparse and grossly unbalanced, allowing them to radiate like a low horizontal antenna. Radials change the efficiency, not the pattern, unless the radials radiate like a dipole. On Wed,8/20/2014 9:05 AM, Tom W8JI wrote: This is because the often poorly understood Fresnel zone extends far beyond practical radial field area, and virtually all of the ground wave attenuation from soil losses is miles from the antenna over the entire long length of a path. It is not localized loss. I agree completely with both of Tom's posts. 73, Jim K9YC You should, he didnt say anything wrong. _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Skimmer calibration
To have an idea of what kind of spread of SNRs one can expect from skimmer reports, I performed a test this morning I recorded two overlapping CQ messages with two different callsigns, one had the sidetone on 500 Hz (EA5RS) and the other at 900 Hz (EA5BY), and applied it to the MIC input of my SSB/USB transceiver (just like you would do in AFSK). I first equalized amplitudes to make sure both tones generated equal output. I then waited for the skimmer reports (and answered to those who called!). So it is the same power, QTH, antenna, . only selective fading can introduce a difference between data reported for both stations Some skimmers reported only one of the calls (some BY, some RS) and some reported both. I cannot guarantee the skimmers decoded both calls exactly at the same time (maybe there are some seconds difference) Here are the reports from the skimmers that decoded both calls at the same minute: 21046.6 EA5RS 19-Aug-2014 0714Z CW 12 dB 34 WPM CQ DJ9IE-# 21047.0 EA5BY 19-Aug-2014 0714Z CW 12 dB 34 WPM CQ DJ9IE-# 21041.6 EA5RS 19-Aug-2014 0711Z CW 27 dB 33 WPM CQ SK3GW-# 21042.0 EA5BY 19-Aug-2014 0711Z CW 25 dB 33 WPM CQ SK3GW-# 21046.6 EA5RS 19-Aug-2014 0708Z CW 22 dB 33 WPM CQ SK3W-# 21047.0 EA5BY 19-Aug-2014 0708Z CW 26 dB 34 WPM CQ SK3W-# 21044.6 EA5RS 19-Aug-2014 0704Z CW 29 dB 34 WPM CQ SK3W-# 21045.0 EA5BY 19-Aug-2014 0704Z CW 30 dB 33 WPM CQ SK3W-# 14047.6 EA5RS 19-Aug-2014 0655Z CW 7 dB 33 WPM CQ DK0TE-# 14048.0 EA5BY 19-Aug-2014 0655Z CW 7 dB 34 WPM CQ DK0TE-# 21044.6 EA5RS 19-Aug-2014 0652Z CW 23 dB 35 WPM CQ SK3GW-# 21045.0 EA5BY 19-Aug-2014 0652Z CW 24 dB 35 WPM CQ SK3GW-# I think this shows averaging is necessary if you want precision measurements. 73 Juan EA5RS -Mensaje original- De: Topband [mailto:topband-boun...@contesting.com] En nombre de Tom W8JI Enviado el: lunes, 18 de agosto de 2014 20:26 Para: topband@contesting.com Asunto: Re: Topband: Skimmer calibration Since no one likely knows the gain of a reference antenna within a dB or so, splitting hairs doesn't matter. Ten dB would jump right out, while 3 dB might get lost in the QSB. When I was comparing high dipoles to verticals on 160, I collected reports for about a year. It was thousands of reports. I probably could have done it in a week or two with skimmer, but then I would have had to repeat it for seasonal changes. I'm sure a good test protocol using skimmer could be worked out. - Original Message - From: Jim Brown j...@audiosystemsgroup.com To: topband@contesting.com Sent: Monday, August 18, 2014 12:47 PM Subject: Re: Topband: Skimmer calibration On Mon,8/18/2014 4:53 AM, Tom W8JI wrote: A live comparison of S/N ratio or relative level over time is with very few exceptions an excellent comparative test. It is much more accurate than S meters or absolute levels without a comparison reference. As such, the RBN is a great tool for evaluating systems. Yes. BUT -- my experience has been that I must average hundreds of data points to get meaningful data. The reasons are simple -- we must contend with QSB, and as Tom noted in another post, nulls in the patterns of antennas at both ends. A few years ago, I tried to compare two 160M antennas using JT65 and W6CQZ's JT65 RBN. On a good night, I would see reports from 3-4 stations east of the Mississippi. I alternated between the two antennas for hours, putting the reports in a spreadsheet, and studying the data. Modelling predicted differences of a few dB, and I never found that the data was good enough to confirm the models. The antennas are passive arrays of fairly tall verticals of a quarter wave or less, so there are no vertical nulls in their pattern. I can clearly hear their directivity on RX, but their gain is what I was trying to confirm. 73, Jim K9YC _ Topband Reflector Archives - http://www.contesting.com/_topband - No virus found in this message. Checked by AVG - www.avg.com Version: 2014.0.4745 / Virus Database: 4007/8057 - Release Date: 08/18/14 _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Skimmer calibration
When I last investigated, all the skimmers and Web SDRs that were outside of North America all had terrible receive antennas for copying DX signals on 160. (And who knows how many of them are in quiet locations?) When I say terrible, I mean small magnetic loops, very short whips, low dipoles, a random end-fed wire, etc. No phased arrays or Beverages, and not even a Flag, K9AY, EWE, etc. Does anyone know if that is still the case? 73, Mike www.w0btu.com _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Skimmer calibration
Sure it is. Most skimmers are setup to receive all directions on more then one band. Anyway, Skimmers only show S/N. 73 Peter -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Mike Waters Sent: Dienstag, 19. August 2014 11:34 To: topband Subject: Re: Topband: Skimmer calibration When I last investigated, all the skimmers and Web SDRs that were outside of North America all had terrible receive antennas for copying DX signals on 160. (And who knows how many of them are in quiet locations?) When I say terrible, I mean small magnetic loops, very short whips, low dipoles, a random end-fed wire, etc. No phased arrays or Beverages, and not even a Flag, K9AY, EWE, etc. Does anyone know if that is still the case? 73, Mike www.w0btu.com _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Skimmer calibration
the gw8izr skimmer seems pretty good to me...dr1a also...both, better than average, IMHO a belgian one also ( can't remember the call..) couple in JA also.. 73, w5xz, dan On Tuesday, August 19, 2014 4:33 AM, Mike Waters mikew...@gmail.com wrote: When I last investigated, all the skimmers and Web SDRs that were outside of North America all had terrible receive antennas for copying DX signals on 160. (And who knows how many of them are in quiet locations?) When I say terrible, I mean small magnetic loops, very short whips, low dipoles, a random end-fed wire, etc. No phased arrays or Beverages, and not even a Flag, K9AY, EWE, etc. Does anyone know if that is still the case? 73, Mike www.w0btu.com _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Skimmer calibration
I quickly noticed that some skimmers seem to have more effective antenna systems than others. More than S/N, I look at kinda the breadth and depth of where I'm spotted. On 160M, GW8IZR and DL1A are where I'm first spotted. If I'm getting spotted more broadly or deeply than that, then I know conditions are really good. Tim N3QE On Tue, Aug 19, 2014 at 5:33 AM, Mike Waters mikew...@gmail.com wrote: When I last investigated, all the skimmers and Web SDRs that were outside of North America all had terrible receive antennas for copying DX signals on 160. (And who knows how many of them are in quiet locations?) When I say terrible, I mean small magnetic loops, very short whips, low dipoles, a random end-fed wire, etc. No phased arrays or Beverages, and not even a Flag, K9AY, EWE, etc. Does anyone know if that is still the case? 73, Mike www.w0btu.com _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Skimmer calibration
Do we really care that skimmers aren't hooked up to antennas with pattern and gain? One of the things in using VOACAP is knowing the pattern of the RX antenna as well as TX. Omni pattern at RX removes RX antenna bias. Why shouldn't we specifically use omni on RX, so that any enhancement is from the sender or the propagation/environment? The thing about sensitivity is that it rarely matters if the out-there-on-the-band noise is controlling. Band-noise controlling is far more common on 160 than 80 and above. Running stuff from here to W4KAZ 7+ miles away always shows an initial 3-4 dB drop in S/N when the band just starts to open. Why I generally run stuff to him in the middle of the day when I want to know the numbers. 73, Guy On Tue, Aug 19, 2014 at 12:06 PM, Tim Shoppa tsho...@gmail.com wrote: I quickly noticed that some skimmers seem to have more effective antenna systems than others. More than S/N, I look at kinda the breadth and depth of where I'm spotted. On 160M, GW8IZR and DL1A are where I'm first spotted. If I'm getting spotted more broadly or deeply than that, then I know conditions are really good. Tim N3QE On Tue, Aug 19, 2014 at 5:33 AM, Mike Waters mikew...@gmail.com wrote: When I last investigated, all the skimmers and Web SDRs that were outside of North America all had terrible receive antennas for copying DX signals on 160. (And who knows how many of them are in quiet locations?) When I say terrible, I mean small magnetic loops, very short whips, low dipoles, a random end-fed wire, etc. No phased arrays or Beverages, and not even a Flag, K9AY, EWE, etc. Does anyone know if that is still the case? 73, Mike www.w0btu.com _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Skimmer calibration
Depends what are you expecting from Skimmer-RX-ANT setup. If you want skimmer to find DX before the pack and looking for low angle signals, then setup better use antenna with proper low angle vertical pattern. Also getting true report when evaluating beach antennas with low vertical angle, skimmer should be using similar antenna to even detect the signals. High angle skimmer antenna would make TX beach vertical vs. horizontal or other antennas inland look about the same and erasing the impossible 10 -20 dB advantage. Just like say if one is driving mobile on the land, you don't hear low angle signals. Get close to the water, or better, bridge over salty water, band comes to life, 10 - 20 dB enhancement becomes reality. Skimmers and testing over longer distances is fine to get ball park idea how, or if the antenna works, but the true indicator of performance is the field strength measurement in the vicinity of antenna, eliminating finicky propagation and other undesirable variables. For unbelievers in salty beach phenomena, I recommend reading K2KW and Team Vertical exploits, tests, measurements http://www.k2kw.com/verticals/verticalinfo.htm and take to the beach with radio and see it, before posting authoritative denials. I did, I knew salt water is good, but wanted to see it with my own ears. I packed 10m setup ( 3el. vertical Omni with Stackmatch) and went to Cape Hatteras, NC. Just driving around the banks, bridges and sandy islands it was an eye and ear opener. Second time I brought 4 square and vertically polarized 2 el. Quad on a boat deck. I saw that 10 - 20 dB difference and the ability to work juicy stuff before packs got to it. (Still US 10m LP record as N2EE/4) I figured 10m would be least advantageous band to take advantage of the effect (low bands would be more enhanced), but I was sitting there unbelieving. Good enough for me, I understand the phenomena, I figured how to take advantage of it and when I get the chance to play I will pack my fishing rods and play on the beach. I don't need skimmer to tell me that. Yuri, K3BU.us www.MVmanor.com for your DXContestvention or ham radio weddings On Tue, Aug 19, 2014 at 05:01 PM, Guy Olinger K2AV wrote: Do we really care that skimmers aren't hooked up to antennas with pattern and gain? One of the things in using VOACAP is knowing the pattern of the RX antenna as well as TX. Omni pattern at RX removes RX antenna bias. Why shouldn't we specifically use omni on RX, so that any enhancement is from the sender or the propagation/environment? The thing about sensitivity is that it rarely matters if the out-there-on-the-band noise is controlling. Band-noise controlling is far more common on 160 than 80 and above. Running stuff from here to W4KAZ 7+ miles away always shows an initial 3-4 dB drop in S/N when the band just starts to open. Why I generally run stuff to him in the middle of the day when I want to know the numbers. 73, Guy On Tue, Aug 19, 2014 at 12:06 PM, Tim Shoppa wrote: I quickly noticed that some skimmers seem to have more effective antenna systems than others. More than S/N, I look at kinda the breadth and depth of where I'm spotted. On 160M, GW8IZR and DL1A are where I'm first spotted. If I'm getting spotted more broadly or deeply than that, then I know conditions are really good. Tim N3QE On Tue, Aug 19, 2014 at 5:33 AM, Mike Waters wrote: When I last investigated, all the skimmers and Web SDRs that were outside of North America all had terrible receive antennas for copying DX signals on 160. (And who knows how many of them are in quiet locations?) When I say terrible, I mean small magnetic loops, very short whips, low dipoles, a random end-fed wire, etc. No phased arrays or Beverages, and not even a Flag, K9AY, EWE, etc. Does anyone know if that is still the case? 73, Mike www.w0btu.com _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Skimmer calibration
Do we really care that skimmers aren't hooked up to antennas with pattern and gain? One of the things in using VOACAP is knowing the pattern of the RX antenna as well as TX. Omni pattern at RX removes RX antenna bias. Why shouldn't we specifically use omni on RX, so that any enhancement is from the sender or the propagation/environment? If I wanted to know what antenna was better, I would use a short vertical or vertically polarized antenna for most applications. Ideally, you want a broad elevation pattern with no nulls. A 2 foot vertical has about the same pattern as a 130 ft vert for elevation on 160, so the only issue is sensitivity falling into RX internal noise. I think people live on the false notion that verticals have a null at near zero, which patterns on Ham models will show, but that is a program display shortfall causing that error. If they really were zero, all broadcast stations would be dark for groundwave. :) _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Skimmer calibration
Do we really care that skimmers aren't hooked up to antennas with pattern and gain? One of the things in using VOACAP is knowing the pattern of the RX antenna as well as TX. Omni pattern at RX removes RX antenna bias. Why shouldn't we specifically use omni on RX, so that any enhancement is from the sender or the propagation/environment? If I wanted to know what antenna was better, I would use a short vertical or vertically polarized antenna for most applications. Ideally, you want a broad elevation pattern with no nulls. A 2 foot vertical has about the same pattern as a 130 ft vert for elevation on 160, so the only issue is sensitivity falling into RX internal noise. I think people live on the false notion that verticals have a null at near zero, which patterns on Ham models will show, but that is a program display shortfall causing that error. If they really were zero, all broadcast stations would be dark for groundwave. :) BC antennas have the elaborate radial system in order to get that groundwave while the typical on ground ham vertical loses a lot of the 0-10 degree (or more) radiation. Go to the beach to get it back.or go with elevated radials. Carl KM1H _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Skimmer calibration
BC antennas have the elaborate radial system in order to get that groundwave while the typical on ground ham vertical loses a lot of the 0-10 degree (or more) radiation. Go to the beach to get it back.or go with elevated radials. That just isn't factual at all. Radials under the vertical antenna have virtually no effect on wave angle unless they are sparse and grossly unbalanced, allowing them to radiate like a low horizontal antenna. Radials change the efficiency, not the pattern, unless the radials radiate like a dipole. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband
Topband: Skimmer calibration
I am not a Skimmer expert, and am just asking. Question: Are all the Skimmers individually(and collectively) calibrated in concert? Can one rely on them for comparing scientific data and conclusion to prove or ascertain a point?Val Val, A live comparison of S/N ratio or relative level over time is with very few exceptions an excellent comparative test. It is much more accurate than S meters or absolute levels without a comparison reference. As such, the RBN is a great tool for evaluating systems. The problems are: 1.) For determining small differences, less than around 5 dB, you have to know the performance level of the reference antenna or station. (For that reason, I use a simple dipole reference.) 2.) The reference and AUT (antenna under test) have to be reasonably close together to eliminate propagation variances, but not so close as to interact, and they have to be in the clear. For example, it would be foolish for me to plant a dipole in the middle of a bunch of Yagi antennas and call it a reference, or put the antenna being evaluated in an obstructed area. 3.) On skywave, there has to be some time involved with readings averaged over time. This is somewhat true if there is more than a few wavelengths distance between antennas, and especially true (almost critical) when comparing different polarization antennas. 4.) Ideally the reference and AUT should be the same polarization, unless we simply want to know which is louder overall. 5.) Antennas have sweet and sour heights for a given set of conditions. We have to be very careful of this. This is especially true when antennas are more than a half wavelength high above ground, because the antenna pattern will be a series of deep nulls that selectively notch out a given wave angle. The RBN is an excellent tool. It does not need to be calibrated in absolute level, only in dB, and dB to noise is just fine provided the noise level of the receive site is steady. One thing I hope we all can do is stop acting so American (we are now what, 30th or 40th in math and science?) and get back to constructive exchanges of information. If we stop learning and just pick a position and fight, which is our trend today, this becomes a useless hobby and there is no reason to communicate. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Skimmer calibration
There's a lot of scatter in the dB measurements from skimmers. If I see dozens of spots graphed on the reversebeacon spots comparison tool then I can believe systemic differences like 3-5dB. But I could never draw that conclusion over a single pair of spots. Any given skimmer will spot a given station on a given frequency at most once every ten minutes. But when the geographic density of skimmers is large enough (e.g. East coast US or Western Europe) just raw quantities or breadth of spots starts being more interesting than exact dB level. Even with the paucity of skimmers on west coast of US, I can still see who has a 4-square for transmit and how they steer it during the contest. Tim N3QE On Mon, Aug 18, 2014 at 7:53 AM, Tom W8JI w...@w8ji.com wrote: I am not a Skimmer expert, and am just asking. Question: Are all the Skimmers individually(and collectively) calibrated in concert? Can one rely on them for comparing scientific data and conclusion to prove or ascertain a point?Val Val, A live comparison of S/N ratio or relative level over time is with very few exceptions an excellent comparative test. It is much more accurate than S meters or absolute levels without a comparison reference. As such, the RBN is a great tool for evaluating systems. The problems are: 1.) For determining small differences, less than around 5 dB, you have to know the performance level of the reference antenna or station. (For that reason, I use a simple dipole reference.) 2.) The reference and AUT (antenna under test) have to be reasonably close together to eliminate propagation variances, but not so close as to interact, and they have to be in the clear. For example, it would be foolish for me to plant a dipole in the middle of a bunch of Yagi antennas and call it a reference, or put the antenna being evaluated in an obstructed area. 3.) On skywave, there has to be some time involved with readings averaged over time. This is somewhat true if there is more than a few wavelengths distance between antennas, and especially true (almost critical) when comparing different polarization antennas. 4.) Ideally the reference and AUT should be the same polarization, unless we simply want to know which is louder overall. 5.) Antennas have sweet and sour heights for a given set of conditions. We have to be very careful of this. This is especially true when antennas are more than a half wavelength high above ground, because the antenna pattern will be a series of deep nulls that selectively notch out a given wave angle. The RBN is an excellent tool. It does not need to be calibrated in absolute level, only in dB, and dB to noise is just fine provided the noise level of the receive site is steady. One thing I hope we all can do is stop acting so American (we are now what, 30th or 40th in math and science?) and get back to constructive exchanges of information. If we stop learning and just pick a position and fight, which is our trend today, this becomes a useless hobby and there is no reason to communicate. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Skimmer calibration
It's also worth mentioning that you can evade the Skimmer's wait 10 minutes before re-spotting limitation simply by QSYing 500 Hz or sobefore re-sending - that way you can get a lot of data points in a relatively short period. So long as you use TEST as your keyword rather than CQ, and stay out of other people's way, nobody should be upset. 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 8/18/2014 12:16 PM, Tom W8JI wrote: This is why some time and multiple skimmers must be involved in the statisticsotherwise data doesn't mean much. Without skimmer I never settled on antennas until many dozens of blind AB test reports. I think skimmer is a more accurate way, because the human at the RX end is out of the picture. There's a lot of scatter in the dB measurements from skimmers. If I see dozens of spots graphed on the reversebeacon spots comparison tool then I can believe systemic differences like 3-5dB. But I could never draw that conclusion over a single pair of spots. Any given skimmer will spot a given station on a given frequency at most once every ten minutes. But when the geographic density of skimmers is large enough (e.g. East coast US or Western Europe) just raw quantities or breadth of spots starts being more interesting than exact dB level. Even with the paucity of skimmers on west coast of US, I can still see who has a 4-square for transmit and how they steer it during the contest. Tim N3QE On Mon, Aug 18, 2014 at 7:53 AM, Tom W8JI w...@w8ji.com wrote: I am not a Skimmer expert, and am just asking. Question: Are all the Skimmers individually(and collectively) calibrated in concert? Can one rely on them for comparing scientific data and conclusion to prove or ascertain a point?Val Val, A live comparison of S/N ratio or relative level over time is with very few exceptions an excellent comparative test. It is much more accurate than S meters or absolute levels without a comparison reference. As such, the RBN is a great tool for evaluating systems. The problems are: 1.) For determining small differences, less than around 5 dB, you have to know the performance level of the reference antenna or station. (For that reason, I use a simple dipole reference.) 2.) The reference and AUT (antenna under test) have to be reasonably close together to eliminate propagation variances, but not so close as to interact, and they have to be in the clear. For example, it would be foolish for me to plant a dipole in the middle of a bunch of Yagi antennas and call it a reference, or put the antenna being evaluated in an obstructed area. 3.) On skywave, there has to be some time involved with readings averaged over time. This is somewhat true if there is more than a few wavelengths distance between antennas, and especially true (almost critical) when comparing different polarization antennas. 4.) Ideally the reference and AUT should be the same polarization, unless we simply want to know which is louder overall. 5.) Antennas have sweet and sour heights for a given set of conditions. We have to be very careful of this. This is especially true when antennas are more than a half wavelength high above ground, because the antenna pattern will be a series of deep nulls that selectively notch out a given wave angle. The RBN is an excellent tool. It does not need to be calibrated in absolute level, only in dB, and dB to noise is just fine provided the noise level of the receive site is steady. One thing I hope we all can do is stop acting so American (we are now what, 30th or 40th in math and science?) and get back to constructive exchanges of information. If we stop learning and just pick a position and fight, which is our trend today, this becomes a useless hobby and there is no reason to communicate. 73 Tom _ Topband Reflector Archives - http://www.contesting.com/_topband - No virus found in this message. Checked by AVG - www.avg.com Version: 2014.0.4745 / Virus Database: 4007/8057 - Release Date: 08/18/14 _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Skimmer calibration
On Mon,8/18/2014 4:53 AM, Tom W8JI wrote: A live comparison of S/N ratio or relative level over time is with very few exceptions an excellent comparative test. It is much more accurate than S meters or absolute levels without a comparison reference. As such, the RBN is a great tool for evaluating systems. Yes. BUT -- my experience has been that I must average hundreds of data points to get meaningful data. The reasons are simple -- we must contend with QSB, and as Tom noted in another post, nulls in the patterns of antennas at both ends. A few years ago, I tried to compare two 160M antennas using JT65 and W6CQZ's JT65 RBN. On a good night, I would see reports from 3-4 stations east of the Mississippi. I alternated between the two antennas for hours, putting the reports in a spreadsheet, and studying the data. Modelling predicted differences of a few dB, and I never found that the data was good enough to confirm the models. The antennas are passive arrays of fairly tall verticals of a quarter wave or less, so there are no vertical nulls in their pattern. I can clearly hear their directivity on RX, but their gain is what I was trying to confirm. 73, Jim K9YC _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Skimmer calibration
Since no one likely knows the gain of a reference antenna within a dB or so, splitting hairs doesn't matter. Ten dB would jump right out, while 3 dB might get lost in the QSB. When I was comparing high dipoles to verticals on 160, I collected reports for about a year. It was thousands of reports. I probably could have done it in a week or two with skimmer, but then I would have had to repeat it for seasonal changes. I'm sure a good test protocol using skimmer could be worked out. - Original Message - From: Jim Brown j...@audiosystemsgroup.com To: topband@contesting.com Sent: Monday, August 18, 2014 12:47 PM Subject: Re: Topband: Skimmer calibration On Mon,8/18/2014 4:53 AM, Tom W8JI wrote: A live comparison of S/N ratio or relative level over time is with very few exceptions an excellent comparative test. It is much more accurate than S meters or absolute levels without a comparison reference. As such, the RBN is a great tool for evaluating systems. Yes. BUT -- my experience has been that I must average hundreds of data points to get meaningful data. The reasons are simple -- we must contend with QSB, and as Tom noted in another post, nulls in the patterns of antennas at both ends. A few years ago, I tried to compare two 160M antennas using JT65 and W6CQZ's JT65 RBN. On a good night, I would see reports from 3-4 stations east of the Mississippi. I alternated between the two antennas for hours, putting the reports in a spreadsheet, and studying the data. Modelling predicted differences of a few dB, and I never found that the data was good enough to confirm the models. The antennas are passive arrays of fairly tall verticals of a quarter wave or less, so there are no vertical nulls in their pattern. I can clearly hear their directivity on RX, but their gain is what I was trying to confirm. 73, Jim K9YC _ Topband Reflector Archives - http://www.contesting.com/_topband - No virus found in this message. Checked by AVG - www.avg.com Version: 2014.0.4745 / Virus Database: 4007/8057 - Release Date: 08/18/14 _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Skimmer calibration
Hi Guys, Thank goodness the QRP-types amongst us all don't seem to be so fixated obsessed with such intricate minute details... If they were, most would probably never even get on the air with their peanut-powered rigs...and why would they? There'd most likely be assaulted by dozens of gurus lurking in the sidelines, ready to advise them that what they are attempting to do goes beyond the realm of possibility. ~73~ de Eddy VE3CUI - VE3XZ _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Skimmer calibration
We were talking about validating or debunking people's RX experience at the shore in various relationships to the edge of salt water. And the anecdota included just about any signal around, on whatever path and whatever TX takeoff angle, not just the signals of a few specific TX stations. Contests would create a maximum number of stations, where signals on a pair or trio of identical RX antennas get reported by a pair or trio of skimmer RX. A test grouping could consist of one antenna were over salt water or at edge, another 500 meters off shore, and another well inland but within 50 km. This would assess the same situations as anecdotal reports, and create enough paired or tripled data to identify differences greater than 2 or 3 dB. It is possible that a single contest might generate 10,000 groupings of over a thousand stations, from the very weak to the quite strong. What will be missing in a recent contest's worth of data apparently is the over salt water data, perhaps a few within 500 meters, and the rest. I don't know of current RBN nodes in the first two categories. They serve the spotting network's users well by not reporting signals at water's edge that a lot of people might not be able to hear. It is one thing to RX at exotic sites with short vertical antennas, and quite another to transmit there, with transmit grade antennas. An RX setup, would use a common vertical, include a power source, RX and CPU and blue tooth or 811g to connect, in a sealed box. The base of each vertical would be 8 feet and use for each box a technology chosen from the RX short vertical techniques. Each setup would be calibrated with a milliwatt source to a very short standard antenna at 100 meters distance to calibrate the band-is-dead background noise. These could be transmitting during during the contest as a beacon. Then we would have the ability to mark ambient noise with an absolute value, thus deriving an absolute signal value for any skimmer s/n reading. Then it's up to program analysis of all the signals that came in during a contest. The basic reference points become certain functions against all the data or complete categories of data. Everything is very large sample analysis. It would be yet to be determined what degree of dB accuracy could be proven. It would be useful to operate these skimmers to a separate server just used for the signal trio, and keep ALL the data readings, instead of using the [necessary for general spotting use] reducing a single skimmer's data release to a skimmer's reading of a given station on a given frequency to once every ten or fifteen minutes. Then it would be simple to remove fades, or measure fade depth, etc in the data analysis math. 73, Guy. _ Topband Reflector Archives - http://www.contesting.com/_topband
