FT-8 mode has been stealing the digital show of late.
Not that it's been all excitement and good news. FT-8 has been pushing into traditional JT65 territory, with so many users active at the same time that it has often seem as though, soon, there would be nothing but FT-8.
So I was glad to see early this morning that 20m was packed full of JT9 signals from across the world. It seems that JT65 is being infringed so much that JT9 is a relatively FT-8 free area to set up shop.
I think this is a good thing. FT-8 is just ridiculously fast, often struggles to decode, and has absolutely no reward merit at all. It really might as well be a fully-automatic points gathering mode. That is not how I do radio, and if the number of JT9 signals fighting back this morning is anything to go by, it's also not the way very many others want radio to go.
Saturday 26 August 2017
Monday 21 August 2017
Solar Eclipse - WSPR Results
Despite being across the Atlantic, the great US eclipse of August 21 2017 was an opportunity to test for any propagation peculiarities into the EU that arise from temporary darkness.
I had a long thought about which band to listen out on for this event. There was a lot of ignoring to do - not of reason, but of opinion flooding out from the US which, understandably enough, was heavily biased towards the low bands.
I settled on 20m.
Interestingly, there did seem to be a marked, transient change in propagation from the US west coast. As soon as totality hit Oregon (17:16UT), W6BSD (a long way off the totality line) and, a few moment later, K7RE (also way off totality), popped up from nowhere. W6BSD was very weak at -28dB S/N, but K7RE hit -15dB at 17:3UT, dropping off a cliff to -24dB ten minutes later. K7RE did not appear again for another two hours, when the eclipse effects were well over and very shallow-angle local sunset propagation briefly took over.
It's clear that essentially no station directly in the path of totality was heard during the eclipse, even though many stations prior to the eclipse were being heard well. The propagation prediction in terms of MUF confirms the experience that signals from the US ought to have been strong until the eclipse ended around UK sunset time. That they were not suggests strongly that transient darkness was suppressing the MUF and, therefore, the received signals.
KG6MC, a station just off the totality path, was heard before, through, and after the eclipse. The overall pattern was quite noisy but did show a distinct reduction in signal strength when it could have been expected to be increasing.
N4EFS was the best example I heard, in that he was received steadily for hours running up to the eclipse, and then vanished about 45 minutes before totality. Again, that is not expected by reference to experience of propagation or the MUF forecast.
I'm sure there will be a more robust and detailed assessment of any effects in the US, where they can be expected to be strong down to the low bands. It remains to be seen if anyone had any interest in a proper assessment across to the EU.
I had a long thought about which band to listen out on for this event. There was a lot of ignoring to do - not of reason, but of opinion flooding out from the US which, understandably enough, was heavily biased towards the low bands.
I settled on 20m.
Interestingly, there did seem to be a marked, transient change in propagation from the US west coast. As soon as totality hit Oregon (17:16UT), W6BSD (a long way off the totality line) and, a few moment later, K7RE (also way off totality), popped up from nowhere. W6BSD was very weak at -28dB S/N, but K7RE hit -15dB at 17:3UT, dropping off a cliff to -24dB ten minutes later. K7RE did not appear again for another two hours, when the eclipse effects were well over and very shallow-angle local sunset propagation briefly took over.
 |
| How MUF ought to have worked out inthe absence of an eclipse. |
It's clear that essentially no station directly in the path of totality was heard during the eclipse, even though many stations prior to the eclipse were being heard well. The propagation prediction in terms of MUF confirms the experience that signals from the US ought to have been strong until the eclipse ended around UK sunset time. That they were not suggests strongly that transient darkness was suppressing the MUF and, therefore, the received signals.
KG6MC, a station just off the totality path, was heard before, through, and after the eclipse. The overall pattern was quite noisy but did show a distinct reduction in signal strength when it could have been expected to be increasing.
N4EFS was the best example I heard, in that he was received steadily for hours running up to the eclipse, and then vanished about 45 minutes before totality. Again, that is not expected by reference to experience of propagation or the MUF forecast.
I'm sure there will be a more robust and detailed assessment of any effects in the US, where they can be expected to be strong down to the low bands. It remains to be seen if anyone had any interest in a proper assessment across to the EU.
FT-8: Another Threat to WSPR
The new FT-8 mode, which has a QRG on 80m of 3.574MHz, has brought with it a very unwelcome further infringement of WSPR, sitting at 3.57260MHz, badly affecting results with that very weak signal mode.
Of course, it's not FT-8 or its creators that's at fault; that lies squarely with operators, many of whom are clearly experienced.
This is highly symptomatic of recent developments in the amateur radio world. Click an icon on a piece of software, think what you're doing is fine because 'the software sets everything up', and mindlessly mess-up other people's hard work.
So, if you operate FT-8 or any other mode near the WSPR section of any band, please accept it takes very little bandspace, and make sure your transmissions are outside of the WSPR portion, making sure to allow for the positive shift due to the tone frequency, which is not the same as the frequency shown on your rig's panel!
 |
| Why transmit outside the WSPR section, when you can mess things up for people? |
Of course, it's not FT-8 or its creators that's at fault; that lies squarely with operators, many of whom are clearly experienced.
This is highly symptomatic of recent developments in the amateur radio world. Click an icon on a piece of software, think what you're doing is fine because 'the software sets everything up', and mindlessly mess-up other people's hard work.
So, if you operate FT-8 or any other mode near the WSPR section of any band, please accept it takes very little bandspace, and make sure your transmissions are outside of the WSPR portion, making sure to allow for the positive shift due to the tone frequency, which is not the same as the frequency shown on your rig's panel!
Friday 18 August 2017
IARU and EURAO: Trouble!
Oh dear!
The European Radio Amateur Organisation claims to be having some trouble with IARU of late.
http://www.eurao.org/en/node/900
Don Beattie, who is mentioned liberally in the link, has been contacted for comment. He responded only by saying there has been 'wildly inaccurate reporting' about contacts between IARU and EURAO.
Given the latest smiley picture placed on EURAO's website to demonstrate some thawing in relations, Beattie's tight lippedness might seem a trifle odd. Perhaps relations aren't quite as cosy as the image attempts to portray? Certainly, this press release from IARU seems to indicate rather a lot of antagonism.
If you would like to find out more about latest events at IARU, you can read what could be the most opaque sets of minutes ever created by humankind here. Given that financial information is rather thin on the ground when it comes to IARU activities, I've asked a few questions of their Secretariat, currently the ARRL. Replies, if any, will be posted as they are received.
The European Radio Amateur Organisation claims to be having some trouble with IARU of late.
http://www.eurao.org/en/node/900
Don Beattie, who is mentioned liberally in the link, has been contacted for comment. He responded only by saying there has been 'wildly inaccurate reporting' about contacts between IARU and EURAO.
Given the latest smiley picture placed on EURAO's website to demonstrate some thawing in relations, Beattie's tight lippedness might seem a trifle odd. Perhaps relations aren't quite as cosy as the image attempts to portray? Certainly, this press release from IARU seems to indicate rather a lot of antagonism.
If you would like to find out more about latest events at IARU, you can read what could be the most opaque sets of minutes ever created by humankind here. Given that financial information is rather thin on the ground when it comes to IARU activities, I've asked a few questions of their Secretariat, currently the ARRL. Replies, if any, will be posted as they are received.
Wednesday 16 August 2017
Antenna Pole Clamp Set - Renovation.
About four years ago, I bought a set of hose ('Jubilee') clamps from Spiderbeam, to prevent the occasional slip of sections in my delta loop-supporting fishing pole.
The price for the clamp set, which is good quality, was then about £25. By now, they are a bit cheaper at £18 and sold at a cost where getting your own clamps, rubber padding and shrink-tubing to make your own kit up is not worthwhile.
Recently, though, the rubber padding that prevents the clamps damaging the pole has reached the end of its life in the strong sunshine, salt-laden air and rain. The rubber splits at the points where it makes contact with the top of the section below it.
The life of the rubber can be extended somewhat by simply turning the clamp upside down and refixing it with the split rubber uppermost, and the undamaged part doing its work by facing into the section below it, preventing slippage.
The great thing about the Spiderbeam clamps is that they are made entirely of stainless steel. This is not true of all 'stainless' clamps. Many feature screw worms that are coated mild steel, which eventually rust.
When the rubber fails completely, I have no need to spend £18 on a complete new set, thanks to the all-stainless clamps. I have just bought 5 metres of compressed neoprene band (3mm thick by 15mm wide) from E-bay, which cost me just £5.95, delivered. That should keep me in antenna clamp padding for the rest of my life!
The price for the clamp set, which is good quality, was then about £25. By now, they are a bit cheaper at £18 and sold at a cost where getting your own clamps, rubber padding and shrink-tubing to make your own kit up is not worthwhile.
Recently, though, the rubber padding that prevents the clamps damaging the pole has reached the end of its life in the strong sunshine, salt-laden air and rain. The rubber splits at the points where it makes contact with the top of the section below it.
 |
| 5m of replacement rubber! |
The life of the rubber can be extended somewhat by simply turning the clamp upside down and refixing it with the split rubber uppermost, and the undamaged part doing its work by facing into the section below it, preventing slippage.
The great thing about the Spiderbeam clamps is that they are made entirely of stainless steel. This is not true of all 'stainless' clamps. Many feature screw worms that are coated mild steel, which eventually rust.
When the rubber fails completely, I have no need to spend £18 on a complete new set, thanks to the all-stainless clamps. I have just bought 5 metres of compressed neoprene band (3mm thick by 15mm wide) from E-bay, which cost me just £5.95, delivered. That should keep me in antenna clamp padding for the rest of my life!
Monday 14 August 2017
Where Amateur Radio is Going Wrong
Recently, I've been looking at 2m/70cm handheld radios for myself and my daughter to keep in contact when out and about.
This proved to be quite an enlightening experience. I've long used simple analogue HTs, which present little obstacle to the straightforward role, never more complex than accessing a repeater, that they fulfil.
I started to wonder whether APRS and digital advancements might make things more interesting and provide important location data.
Apart from the very high price (ca. £400 for the latest digital, APRS-equipped HT), it quickly became clear that user friendliness is lagging very seriously behind the general consumer electronics scene.
Take, for example, sending texts on a HT keypad. Compared to a smartphone software keyboard, a HT is like going back to the 1980s. Slow, cumbersome and prone to error. APRS is simple on a smartphone, but rather fidgety on a HT. The bulk of a HT is also a considerable burden.
This is all-too-reminiscent of asking a computer expert how to do something simple on a PC: they will give you the most convoluted, complex way of doing it! If we want to attract newcomers and, especially, younger members to the hobby then all transceivers, from HTs up, need to adopt the kind of user-friendliness that smartphones have used to such spectacular effect. There is no future in making things complex for the sake of feeling superior. If we don't all change - soon - there will be no operators to feel superior about anything!
This proved to be quite an enlightening experience. I've long used simple analogue HTs, which present little obstacle to the straightforward role, never more complex than accessing a repeater, that they fulfil.
I started to wonder whether APRS and digital advancements might make things more interesting and provide important location data.
Apart from the very high price (ca. £400 for the latest digital, APRS-equipped HT), it quickly became clear that user friendliness is lagging very seriously behind the general consumer electronics scene.
Take, for example, sending texts on a HT keypad. Compared to a smartphone software keyboard, a HT is like going back to the 1980s. Slow, cumbersome and prone to error. APRS is simple on a smartphone, but rather fidgety on a HT. The bulk of a HT is also a considerable burden.
This is all-too-reminiscent of asking a computer expert how to do something simple on a PC: they will give you the most convoluted, complex way of doing it! If we want to attract newcomers and, especially, younger members to the hobby then all transceivers, from HTs up, need to adopt the kind of user-friendliness that smartphones have used to such spectacular effect. There is no future in making things complex for the sake of feeling superior. If we don't all change - soon - there will be no operators to feel superior about anything!
Sunday 13 August 2017
Putting ITUProp to the test
There aren't too many WSPR stations emitting from the far northern regions of the world.
Over the past few weeks, a Canadian ship has been making its way along the North West Passage, running a 200mW WSPR beacon as it goes.
It's become clear that CG3EXP, the beacon on the ship, is heard quite consistently around 16:00UT daily, here in Wales. The tiny signal generates a receive report here of around -20dB SNR.
How does the ITU propagation webware fare against this reality-check?
Here's the point-to-point prediction, based on the last known position of the ship and my receiving position.
Clearly, the prediction is pretty accurate!
Over the past few weeks, a Canadian ship has been making its way along the North West Passage, running a 200mW WSPR beacon as it goes.
It's become clear that CG3EXP, the beacon on the ship, is heard quite consistently around 16:00UT daily, here in Wales. The tiny signal generates a receive report here of around -20dB SNR.
How does the ITU propagation webware fare against this reality-check?
Here's the point-to-point prediction, based on the last known position of the ship and my receiving position.
Clearly, the prediction is pretty accurate!
Friday 11 August 2017
Ship Ahoy! CG3EXP on WSPR
 |
| The Polar Prince, carrying a 200mW WSPR beacon. Image: Canada C3 program. |
Have you heard of the CG3EXP voyage around the north west passage of Canada?
Sadly, I hadn't heard a thing about it until yesterday. As soon as I started listening, the WSPR beacon at 200mW popped up on my screen at a good signal strength, despite being a mere 200mW from a pretty tough area of the world.
Details of the voyage can be found here.
The transmitter is a QRP labs US3 unit, transmitting on the 40, 30 and 20m bands. Interestingly, transmissions are showing a couple Hz of drift, which is not something one sees with the comparable WSPRlite units.
So far, I've had a handful of good spots of the ship, which is no mean feat because only about 10 stations at most over several hours have also heard the beacon.
WSPR-X vs. WSJT-X WSPR Mode
WSPR is a mode that has gone from strength to strength recently. With the advent of WSPRlite, albeit only a transmitter, the mode has now edged into the backpacks of DX-peditions and even scientific explorations.
For quite a while, I've been using WSPR-X, which is an experimental mode. It does very well, although it does suffer from a persistent tendency, at least on my equipment, to miss a fraction of the signals evident on-screen.
This morning, after much playing around with receive input settings, I decided to have a go at using the WSPR setting available under WSJT-X.
The difference in remarkable! Whereas WSPR-X might decode a maximum of about eight signals per cycle, WSJT-X reliably pulls out about 15 signals! That's quite a difference, and vitally important for decoding those tiny WSPRlite transmissions from distant places of only a few mW.
I'm not sure why WSPR-X is so poor at decoding. It was a release mainly aimed at announcing WSPR-15. Perhaps WSPR-2 wasn't improved at that point?
I've also found that the derivative software, JTDX, decodes far more transmissions than WSPR-X, broadly in keeping with the rate decoded by WSJT-X.
For quite a while, I've been using WSPR-X, which is an experimental mode. It does very well, although it does suffer from a persistent tendency, at least on my equipment, to miss a fraction of the signals evident on-screen.
This morning, after much playing around with receive input settings, I decided to have a go at using the WSPR setting available under WSJT-X.
The difference in remarkable! Whereas WSPR-X might decode a maximum of about eight signals per cycle, WSJT-X reliably pulls out about 15 signals! That's quite a difference, and vitally important for decoding those tiny WSPRlite transmissions from distant places of only a few mW.
I'm not sure why WSPR-X is so poor at decoding. It was a release mainly aimed at announcing WSPR-15. Perhaps WSPR-2 wasn't improved at that point?
I've also found that the derivative software, JTDX, decodes far more transmissions than WSPR-X, broadly in keeping with the rate decoded by WSJT-X.
Tuesday 8 August 2017
WSPRlite Power Test - Results
Following on from the last post, I decided to carefully look at my WSPRlite unit and test its power output against that set, using a calibrated oscilloscope.
The results are as follows:
At 14MHz:
200mW set: 176mW measured output
100mW set: 114mW
50mW set: 57.6mW
20mW set: 23.6mW
10mW set: 11.8mW
5mW set: 5.2mW
I haven't conducted a comprehensive test at other frequencies. But, I did notice a drop to 144mW at 10MHz when 200mW was set. I will look at this in more detail in the near future. By 7MHz, the drop was to 168mW, rising to 189mW at 3.5MHz.
The results are as follows:
At 14MHz:
200mW set: 176mW measured output
100mW set: 114mW
50mW set: 57.6mW
20mW set: 23.6mW
10mW set: 11.8mW
5mW set: 5.2mW
I haven't conducted a comprehensive test at other frequencies. But, I did notice a drop to 144mW at 10MHz when 200mW was set. I will look at this in more detail in the near future. By 7MHz, the drop was to 168mW, rising to 189mW at 3.5MHz.
Saturday 5 August 2017
WSPRlite - What's Half a Decibel Between Friends?
Power measurement has been the flavour of the week here at Copper Mountain HQ.
Inevitably, attention has turned to the extraordinarily-successful WSPRlite unit, which is marketed as an "antenna performance analysis system" (WSPRlite web page accessed 21:25UT 05/08/2017).
Although the output of the WSPRlite is tiny - just 200mW at most - it is, nevertheless, readily measurable with an oscilloscope.
Now, power measurement that is traceable to a known, stable standard is something we would all like to have, but few ever get a chance (or the means) of owning. So my own measurements, even with a calibrated oscilloscope, have to be taken with a considerable degree of caution.
My scope showed a somewhat lower output than 200mW, and I know of others who have measured around 170mW at 200mW set. If - and I stress if - there is a significant difference between set and actual output, then that is not unusual for any instrument, no matter how expensive, and we do always have to keep in mind this particular unit sells for quite a low price.
The problem for the end-user of WSPRlite is that he/she has no idea, other than relying on the selected set value, what that particular unit is putting out on any given transmission. I certainly wasn't provided with a calibration certificate or statement of output accuracy when I bought mine, nor when I received a replacement when that failed. I couldn't find any reference in current documents to power accuracy in the instructions or FAQs published online (accessed 07/08/2017).
This is odd, because SOTABEAMS appear to be aware of the need for accuracy. This is what they say on their web site (accessed 07/08/2017):
'WSPRlite has accurate digital power control over a 16 dB range to facilitate precise measurements of antenna performance differences.'
Note what appears to be a conflation of accuracy and precision in that sentence. They are not the same thing. It is possible to be accurate with low precision. The graphic below illustrates:
Contact with SOTABEAMS today gave a very brief response that the "spec is +/-0.5dB". Without any elaboration from the company, I am taking that to mean that each unit yields that degree of power output accuracy at any one time, relative to the set value. An alternative possible interpretation could be that each unit, once assembled, always transmits with a fixed deviation within the stated range from the set value.
I was also told that SOTABEAMS "measure" the ouput (presumably on an ongoing sample of manufactured units), using an "in-spec Agilent power meter". I wasn't told which Agilent unit (the company is now known as Keysight), nor was any information on how that unit, in turn, is kept calibrated on an ongoing basis against a known, independent reference standard.
The trouble with trying to be scientifically-accurate is that it is hard.
The stated accuracy is very good for such an affordable and widely-available unit. But we must always keep in mind that declared purpose: to analyse antenna performance (with both accuracy and precision). That often means (and the associated DXPlorer webware features heavily leans towards) comparisons with other antenna systems using the same kind of WSPRlite unit. Accuracy of actual vs. set power output is therefore undeniably important to the end-user where any comparison with another user is being undertaken.
If one unit is running at +0.5dB somewhere, and another happens to be running at -0.5dB, there is obviously a maximum potential inter-station output difference of 1dB.
At a set value of 200mW, this equates to outputs of 224mW at +0.5dB, and 178mW at -0.5dB. Or, a difference of 46mW between highest and lowest potential outputs. And that is assuming the power output accuracy is always within the stated range.
Whether this difference of +/- 11% or so in output is of significance in the real world of reception reports is up for debate, and comments of a reasonable nature are always welcome. My own view is that this - being almost 1/20th of a Watt -is sufficient for a clear difference to appear in received signal strength and reach.
Indeed, because there is a 50mW and 5mW setting (or 50mw and 100mW) on the WSPRlite unit, it is quite easy to run a real comparison of the difference 46mW makes, provided the antennas are exactly the same systems and located in the same environment (and these aspects are absolutely crucial), and run at the same time.
I suppose it does act, at least, as a starting point for getting the inter-unit differences down even lower sometime in the future.
Inevitably, attention has turned to the extraordinarily-successful WSPRlite unit, which is marketed as an "antenna performance analysis system" (WSPRlite web page accessed 21:25UT 05/08/2017).
Although the output of the WSPRlite is tiny - just 200mW at most - it is, nevertheless, readily measurable with an oscilloscope.
Now, power measurement that is traceable to a known, stable standard is something we would all like to have, but few ever get a chance (or the means) of owning. So my own measurements, even with a calibrated oscilloscope, have to be taken with a considerable degree of caution.
My scope showed a somewhat lower output than 200mW, and I know of others who have measured around 170mW at 200mW set. If - and I stress if - there is a significant difference between set and actual output, then that is not unusual for any instrument, no matter how expensive, and we do always have to keep in mind this particular unit sells for quite a low price.
The problem for the end-user of WSPRlite is that he/she has no idea, other than relying on the selected set value, what that particular unit is putting out on any given transmission. I certainly wasn't provided with a calibration certificate or statement of output accuracy when I bought mine, nor when I received a replacement when that failed. I couldn't find any reference in current documents to power accuracy in the instructions or FAQs published online (accessed 07/08/2017).
This is odd, because SOTABEAMS appear to be aware of the need for accuracy. This is what they say on their web site (accessed 07/08/2017):
'WSPRlite has accurate digital power control over a 16 dB range to facilitate precise measurements of antenna performance differences.'
Note what appears to be a conflation of accuracy and precision in that sentence. They are not the same thing. It is possible to be accurate with low precision. The graphic below illustrates:
Contact with SOTABEAMS today gave a very brief response that the "spec is +/-0.5dB". Without any elaboration from the company, I am taking that to mean that each unit yields that degree of power output accuracy at any one time, relative to the set value. An alternative possible interpretation could be that each unit, once assembled, always transmits with a fixed deviation within the stated range from the set value.
I was also told that SOTABEAMS "measure" the ouput (presumably on an ongoing sample of manufactured units), using an "in-spec Agilent power meter". I wasn't told which Agilent unit (the company is now known as Keysight), nor was any information on how that unit, in turn, is kept calibrated on an ongoing basis against a known, independent reference standard.
The trouble with trying to be scientifically-accurate is that it is hard.
The stated accuracy is very good for such an affordable and widely-available unit. But we must always keep in mind that declared purpose: to analyse antenna performance (with both accuracy and precision). That often means (and the associated DXPlorer webware features heavily leans towards) comparisons with other antenna systems using the same kind of WSPRlite unit. Accuracy of actual vs. set power output is therefore undeniably important to the end-user where any comparison with another user is being undertaken.
If one unit is running at +0.5dB somewhere, and another happens to be running at -0.5dB, there is obviously a maximum potential inter-station output difference of 1dB.
At a set value of 200mW, this equates to outputs of 224mW at +0.5dB, and 178mW at -0.5dB. Or, a difference of 46mW between highest and lowest potential outputs. And that is assuming the power output accuracy is always within the stated range.
Whether this difference of +/- 11% or so in output is of significance in the real world of reception reports is up for debate, and comments of a reasonable nature are always welcome. My own view is that this - being almost 1/20th of a Watt -is sufficient for a clear difference to appear in received signal strength and reach.
Indeed, because there is a 50mW and 5mW setting (or 50mw and 100mW) on the WSPRlite unit, it is quite easy to run a real comparison of the difference 46mW makes, provided the antennas are exactly the same systems and located in the same environment (and these aspects are absolutely crucial), and run at the same time.
I suppose it does act, at least, as a starting point for getting the inter-unit differences down even lower sometime in the future.
Thursday 3 August 2017
Yaesu FT-450 Power Measurements.
Last week, after some lurking on E-bay, I managed to get a basic 20MHz CRT oscilloscope for just £25.
Now, I got a first in astronomy, not electronics, so I'm perfectly content to be an avid learner, not an expert.
I happened upon these two useful pages (a) and (b), which led me on the route to make my own RF sampler, and some measurements on my trusty Yaesu FT-450.
So, last evening, I set about some careful measurements with a calibrated scope. As my scope is only a 20MHz bandwidth model, I stopped at 14MHz.
Here are the results, which are quite revealing. For uses like WSPR, the reported errors are significant. Accurate power measurement is not particularly easy or cheap, but is of considerable importance to many of us. There must be quite a market out there for someone who can make an affordable, accurate power meter!
1.8MHZ
Set 5W; Actual = 4.83W
Set 10W; Actual = 8.41W
Set 20W; Actual = 16.00W
Set 50W; Actual = 42.89W
Set 100W; Actual = 72.23W
Mean error: 16.26% below set value
3.5MHz
Set 5W; Actual = 4.83W
Set 10W; Actual =9.30W
Set 20W; Actual = 18.48W
Set 50W; Actual = 43.55W
Set 100W; Actual = 76.54W
Mean error: 10.87% below set value
5.2MHz
Set 5W; Actual = 4.83W
Set 10W; Actual = 8.41W
Set 20W; Actual = 16.00W
Set 50W; Actual = 42.23W
Set 100W; Actual = 80.98W
Mean error: 14.77% below set value
7.1MHz
Set 5W; Actual = 4.83W
Set 10W; Actual = 9.61W
Set 20W; Actual = 17.63W
Set 50W; Actual = 48.99W
Set 100W; Actual = 80.98W
Mean error: 8.03% below set value
10.1MHz
Set 5W; Actual = 7.02W
Set 10W; Actual = 13.69W
Set 20W; Actual = 24.50W
Set 50W; Actual = 56.23W
Set 100W; Actual = 99.97W
Mean error: 22.37% above set value
14.1MHz
Set 5W; Actual = 7.83W
Set 10W; Actual = 14.44W
Set 20W; Actual = 26.00W
Set 50W; Actual = 60.04W
Set 100W; Actual = 115.53W
Mean error: 33.32% over set value
Now, I got a first in astronomy, not electronics, so I'm perfectly content to be an avid learner, not an expert.
I happened upon these two useful pages (a) and (b), which led me on the route to make my own RF sampler, and some measurements on my trusty Yaesu FT-450.
 |
| An aluminium box, two SO239 connectors, a 470 KOhm (top) and 470 Ohm resistor, plus a 10nF capacitor completing the connection to a BNC panel outlet. The overall RF sampled is ~ input Volts/1000. With a 1.5mm copper link between the centre pins of the SO239s, and a piece of metal shim connected to the box sides lying very close, and separated by thin plastic, the analyser-measured SWR of the box into a dummy load is 1.18:1. |
So, last evening, I set about some careful measurements with a calibrated scope. As my scope is only a 20MHz bandwidth model, I stopped at 14MHz.
Here are the results, which are quite revealing. For uses like WSPR, the reported errors are significant. Accurate power measurement is not particularly easy or cheap, but is of considerable importance to many of us. There must be quite a market out there for someone who can make an affordable, accurate power meter!
1.8MHZ
Set 5W; Actual = 4.83W
Set 10W; Actual = 8.41W
Set 20W; Actual = 16.00W
Set 50W; Actual = 42.89W
Set 100W; Actual = 72.23W
Mean error: 16.26% below set value
3.5MHz
Set 5W; Actual = 4.83W
Set 10W; Actual =9.30W
Set 20W; Actual = 18.48W
Set 50W; Actual = 43.55W
Set 100W; Actual = 76.54W
Mean error: 10.87% below set value
5.2MHz
Set 5W; Actual = 4.83W
Set 10W; Actual = 8.41W
Set 20W; Actual = 16.00W
Set 50W; Actual = 42.23W
Set 100W; Actual = 80.98W
Mean error: 14.77% below set value
7.1MHz
Set 5W; Actual = 4.83W
Set 10W; Actual = 9.61W
Set 20W; Actual = 17.63W
Set 50W; Actual = 48.99W
Set 100W; Actual = 80.98W
Mean error: 8.03% below set value
10.1MHz
Set 5W; Actual = 7.02W
Set 10W; Actual = 13.69W
Set 20W; Actual = 24.50W
Set 50W; Actual = 56.23W
Set 100W; Actual = 99.97W
Mean error: 22.37% above set value
14.1MHz
Set 5W; Actual = 7.83W
Set 10W; Actual = 14.44W
Set 20W; Actual = 26.00W
Set 50W; Actual = 60.04W
Set 100W; Actual = 115.53W
Mean error: 33.32% over set value
Subscribe to:
Posts (Atom)