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| 10m WSPR reports late this afternoon |
6 Feb 2013
10m WSPR
137kHz E-field probe on my website
The whole unit is fixed to a car mag-mount antenna and works very well indeed.
5 Feb 2013
OFCOM licence exempt loopholes
Still trying to see if there are any loopholes that would allow me to legally carry out radiated tests between 40-80kHz as mentioned in earlier posts.
Currently I'm pondering an OFCOM document called IR 2030 - UK Interface Requirements 2030 Licence Exempt Short Range Devices . This document seems to offer some hope by adopting the licence exemptions applicable to short range devices such as metal detectors and induction communications systems. For example, for metal detectors, it says,
"That part of an induction system designed or adapted to produce:- (a) a controlled magnetic field; and (b) a predetermined recognisable signal when operating within that magnetic field"
in the frequency range 9 - 148.5 kHz the emission level is [not greater than] 70 dBμA/m at 6 m. My maths is not good, but this is 3.15mA/m which sounds quite a lot. Some other specifications allow 72dBuA/m at 10m, which is considerably more. It seems I need to read a copy of document EN 300 330-2 which describes the rules and test methods. Although these rules are designed for systems that use induction field communications, the unknown is how much signal that meets these requirements might be radiated and detectable with sensitive kit in the far field?
Incidentally, it is surprising how many non-amateur frequencies can be used legally with (useful) QRPp power levels in the MF, HF, VHF range, no doubt with some type approval stipulation or at least CE declarations being required on the equipment. With WSPR or similar weak signal modulation systems, some most interesting experiments could be carried out in unusual parts of the LF, MF, HF and VHF spectrum, apparently without a licence being needed, as long as the emissions limits are met.
Currently I'm pondering an OFCOM document called IR 2030 - UK Interface Requirements 2030 Licence Exempt Short Range Devices . This document seems to offer some hope by adopting the licence exemptions applicable to short range devices such as metal detectors and induction communications systems. For example, for metal detectors, it says,
"That part of an induction system designed or adapted to produce:- (a) a controlled magnetic field; and (b) a predetermined recognisable signal when operating within that magnetic field"
in the frequency range 9 - 148.5 kHz the emission level is [not greater than] 70 dBμA/m at 6 m. My maths is not good, but this is 3.15mA/m which sounds quite a lot. Some other specifications allow 72dBuA/m at 10m, which is considerably more. It seems I need to read a copy of document EN 300 330-2 which describes the rules and test methods. Although these rules are designed for systems that use induction field communications, the unknown is how much signal that meets these requirements might be radiated and detectable with sensitive kit in the far field?
Incidentally, it is surprising how many non-amateur frequencies can be used legally with (useful) QRPp power levels in the MF, HF, VHF range, no doubt with some type approval stipulation or at least CE declarations being required on the equipment. With WSPR or similar weak signal modulation systems, some most interesting experiments could be carried out in unusual parts of the LF, MF, HF and VHF spectrum, apparently without a licence being needed, as long as the emissions limits are met.
OFCOM ..."no you can't" again at LF
This afternoon I got another email from OFCOM. Although my requests have been passed upwards for other more empowered people to consider, it is effectively a refusal of permission to carry out experimental research for short periods even at 10uW EIRP on clear spot frequencies in the LF spectrum between 40 and 80kHz without getting a £50 Non Operational (T&D) Licence, which I am not prepared to do.
Thank you Mark VK6WV
Amateur radio has some very kind and generous people still.
In the post today I received a letter from Australia quite unexpectedly. In it were a number of 480kHz ceramic resonators that Mark VK6WV had sent me, as a gift, for me to try in a 472kHz transmitter. Mark, many thanks! This was a very nice surprise in the best spirit of amateur radio. I shall indeed use these to build a little 472kHz tunable CW transmitter. I'll also try using these in an RF stage of a receiver for the 472kHz band.
This is not the first time I have been on the receiving end of generous fellow amateurs and it is so lovely to know that there are kind people about who simply want to give and to share. Mark didn't even give me an email address that I could use to thank him, so I am doing so here via the blog.
Wonderful! You made my day Mark.
In the post today I received a letter from Australia quite unexpectedly. In it were a number of 480kHz ceramic resonators that Mark VK6WV had sent me, as a gift, for me to try in a 472kHz transmitter. Mark, many thanks! This was a very nice surprise in the best spirit of amateur radio. I shall indeed use these to build a little 472kHz tunable CW transmitter. I'll also try using these in an RF stage of a receiver for the 472kHz band.
This is not the first time I have been on the receiving end of generous fellow amateurs and it is so lovely to know that there are kind people about who simply want to give and to share. Mark didn't even give me an email address that I could use to thank him, so I am doing so here via the blog.
Wonderful! You made my day Mark.
137kHz 30-40W TX transverter schematic
As promised, here is the schematic of the current 30-40W TX transverter for 137kHz. I have used a 10MHz crystal but a lower local oscillator frequency would be slightly better from a stability viewpoint when using narrowband modes like QRSS30 or WSP15. One choice is to use a low cost 1.843kHz crystal mixing with the driver transmitter's output at 1.979kHz. When a stable external LO source is possible e.g. a GPS disciplined oscillator, remove C7 and feed the LO into the double balanced mixer. Although an SBL-1 mixer was used an alternative, available from eBay is the ADE-1. As balance is not super critical, a home made double balanced mixer would also be possible.
For PA heatsink I just used a couple of small TO220 heatsinks in the prototype. With optimal PA matching into 50 ohms there is little heat from the PA device. A larger heatsink could prevent overheating when the antenna is mismatched. My output network was optimised for my slightly higher than 50 ohms output load presented by my earth electrode antenna.
ERP is around 30uW with my earth-electrode antenna.
Some may prefer to use capacitive coupling into the FET gate. If TR3 failed open circuit, the gate voltage would rise leading to the IRF640 failing. Hasn't been a problem so far though.
ERP is around 30uW with my earth-electrode antenna.
Some may prefer to use capacitive coupling into the FET gate. If TR3 failed open circuit, the gate voltage would rise leading to the IRF640 failing. Hasn't been a problem so far though.
4 Feb 2013
A dialogue with OFCOM
At last, and only 3 months late, OFCOM have renewed my NoV for 8.7-9.1kHz VLF operation.
Currently I am "in negotiation" with OFCOM on another matter mentioned a few days ago.
In the next few months I want to do some QRPp radiated tests with the earth-electrode antennas at some frequencies between 9kHz and 137kHz. Ideally this would be around 35-45kHz and 70-80kHz, where I can find a quiet spot without any activity from primary users like the Ministry of Defence. With QRSS, continuous carrier or WSPR and with an EIRP of around 10uW it should be interesting. Tests on 137kHz suggest this power is enough to see a radiated signal out to at least 25km locally with an E-field probe on the car, which would allow me to check coverage and polar plot. On the lower frequencies this may be limited to just 5-10km, but that would be OK.
But, OFCOM say they will not grant me licence-exempt permission to operate in this part of the spectrum, even at the miniscule powers and bandwidth (uWs and a few Hz).
They say they would HAVE to consult with the primary users and this would take months. They suggest instead I apply for a Non Operational (Test and Development) Licence, but does that not need primary user approval too? Problem is this licence costs £50 a year, which sounds like total overkill when the risk of me interfering with anyone is about as likely as me winning the lottery or landing on the moon when I jump.
Now, I could just go ahead and do the tests anyway knowing I will not cause anyone a problem. Really this is not the way it should be and anyway I'd like to publish the results later. Hardly possible if I don't do things with OFCOM's approval. I am hoping that the good people at OFCOM will see that this is worthwhile amateur research, it won't cause ANY issues and they will soon say, "go ahead on the strict understanding that if you cause any harmful interference to primary users you close down immediately, but at that power, no licence needed." I have written back to OFCOM again this evening making this case and we'll what transpires. I also suggested issuing me a one-off NoV, but they say they won't!
Many of you will be saying, "why not just do it". If the powers that be really cannot see sense, then maybe I may have no other option.
Currently I am "in negotiation" with OFCOM on another matter mentioned a few days ago.
In the next few months I want to do some QRPp radiated tests with the earth-electrode antennas at some frequencies between 9kHz and 137kHz. Ideally this would be around 35-45kHz and 70-80kHz, where I can find a quiet spot without any activity from primary users like the Ministry of Defence. With QRSS, continuous carrier or WSPR and with an EIRP of around 10uW it should be interesting. Tests on 137kHz suggest this power is enough to see a radiated signal out to at least 25km locally with an E-field probe on the car, which would allow me to check coverage and polar plot. On the lower frequencies this may be limited to just 5-10km, but that would be OK.
But, OFCOM say they will not grant me licence-exempt permission to operate in this part of the spectrum, even at the miniscule powers and bandwidth (uWs and a few Hz).
They say they would HAVE to consult with the primary users and this would take months. They suggest instead I apply for a Non Operational (Test and Development) Licence, but does that not need primary user approval too? Problem is this licence costs £50 a year, which sounds like total overkill when the risk of me interfering with anyone is about as likely as me winning the lottery or landing on the moon when I jump.
Now, I could just go ahead and do the tests anyway knowing I will not cause anyone a problem. Really this is not the way it should be and anyway I'd like to publish the results later. Hardly possible if I don't do things with OFCOM's approval. I am hoping that the good people at OFCOM will see that this is worthwhile amateur research, it won't cause ANY issues and they will soon say, "go ahead on the strict understanding that if you cause any harmful interference to primary users you close down immediately, but at that power, no licence needed." I have written back to OFCOM again this evening making this case and we'll what transpires. I also suggested issuing me a one-off NoV, but they say they won't!
Many of you will be saying, "why not just do it". If the powers that be really cannot see sense, then maybe I may have no other option.
Website working again
The main www.g3xbm.co.uk website is now working properly. I contacted my domain providers last night who confirmed they'd updated some systems that screwed up web forwarding. If you spot any more problems, typos or link errors please let me know.
Currently I am drawing out the schematic of my 30W 137kHz TX transverter. This should be on the website tomorrow. Still deciding whether to box it, and add the RX preamp section, or stop at this stage.
Currently I am drawing out the schematic of my 30W 137kHz TX transverter. This should be on the website tomorrow. Still deciding whether to box it, and add the RX preamp section, or stop at this stage.
Simple low cost test equipment
There was an interesting post in the last day on the GQRP Yahoo group asking about portable workbenches that led on to talk about test equipment. This got me thinking about simple pieces of test equipment and what one needs to do basic QRP design work.
In my own case the most useful pieces of kit are (1) a signal generator, (2) an inductance/capacitance meter, (3) an oscilloscope,(4) a basic power meter, (5) a wide coverage all mode RX, (6) a multimeter. I keep thinking about building a dead basic spectrum analyser too. Test probes too of course. Also a good lot of cables with BNC plugs one end and croc clips on the other.
Just wondering what other people use? Certainly for HF QRP work only very basic test gear is needed, which is why I enjoy it so much.
In a way it is a little surprising that no-one sells a low cost "all in one" test box for amateurs with many of the above in one unit. A bit like a CB test box?
In my own case the most useful pieces of kit are (1) a signal generator, (2) an inductance/capacitance meter, (3) an oscilloscope,(4) a basic power meter, (5) a wide coverage all mode RX, (6) a multimeter. I keep thinking about building a dead basic spectrum analyser too. Test probes too of course. Also a good lot of cables with BNC plugs one end and croc clips on the other.
Just wondering what other people use? Certainly for HF QRP work only very basic test gear is needed, which is why I enjoy it so much.
In a way it is a little surprising that no-one sells a low cost "all in one" test box for amateurs with many of the above in one unit. A bit like a CB test box?
3 Feb 2013
Not the best of weeks
Well, apart from the excitement over the ferrite rod on TX, this has not been a too brilliant week.
As you saw in the last post, my website domain name provider seems to have messed up web forwarding thereby screwing up the G3XBM website, for now at least. This is annoying as it has also caused issues on the www.cambschoral.org.uk website that I set up and maintain for the Cambridgeshire Choral Society. And then there is 137kHz where a week of trying has netted me spots from just 4 unique reporters. Even the effort to get WSPR15 working was all but scuppered by the 4Hz drift over 15 minutes in the FT817.
In the grand scheme of things none of this much matters. Perhaps next week will be more fruitful, HI. In the meantime, I'm watching TV and having a whisky!
As you saw in the last post, my website domain name provider seems to have messed up web forwarding thereby screwing up the G3XBM website, for now at least. This is annoying as it has also caused issues on the www.cambschoral.org.uk website that I set up and maintain for the Cambridgeshire Choral Society. And then there is 137kHz where a week of trying has netted me spots from just 4 unique reporters. Even the effort to get WSPR15 working was all but scuppered by the 4Hz drift over 15 minutes in the FT817.
In the grand scheme of things none of this much matters. Perhaps next week will be more fruitful, HI. In the meantime, I'm watching TV and having a whisky!
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