Monday, July 16, 2012
Radio Kiribati 1440 Verification
I've had a rule in later years not to send reception reports to stations I hear, but no rules without exceptions. Radio Kiribati's new transmitter on 1440 (replacing 846) was audible with surprising quality last October. Today I received a friendly response from Babera Marewenimakin. Thanks Bryan Clark for finding the correct email address.
Sunday, July 08, 2012
When You Need To Get Rid Of That Noise
Receivers are not immune to very strong signals. And they exist - it could be your local AM station, the general signal level in your part of the world, or that your radio simply cannot handle the signal level.
Conventional receivers often had a tracking preselector which helped attenuating signals outside of its passband. Older receivers more often used a manual preselector. With the advent of software defined radios, capable of recording from 192 kHz up to 4 MHz, a preselector loses its relevance. Some SDRs are "wide open", while others use a set of bandpass filters. The RF Space NetSDR for instance uses 10 sub-octave filters. The Winradio G33DDC has14 configurable bandpass filters. The Afedri SDR-net on the other side has none, while the G31DDC has a selectable high pass filter to reduce MW interference on SW.
My 100 kHz notch filter was designed by Swedish DX-er Stefan Wikander, is easy to build and was later refined by Dallas Lankford who added a 500 kHz high pass filter to the design. Read more here.
When it comes to high pass and low pass filters, there is a limited amount of off-the-shelf products. Tracey Gardner kindly directed me to the Minicircuits range of filters. Unfortunately, almost all their products are aimed at higher frequency ranges, but they have some interesting low pass filters. For the MW DX-er, the 1.9 MHz filter could be very suitable. In addition, the filters are very small with a female BNC on one end and a male BNC on the other. At around USD 35, they are quite inexpensive, too.
Other than that, it seems that you have to rely on small, dedicated enterprises. They will charge you more, but the products can be tailor-made for you, and quality will be excellent. Here are a couple of interesting manufacturers:
Clifton Laboratories offer active antennas, amplifiers, filters and other items of interest for the DX-er and radio amateur. The proprietor Jack Smith makes bandpass filters, band rejection filters, high pass filters and low pass filters with superb characteristics. They can be built to meet customers requirements. The price range is USD 40-70, metal cased with connectors. More details on their web page. My low pass filter was bought (un-boxed) from Clifton Laboriatories.
Kiwa Electronics has been around for decades. Kiwa offers a wide range of low pass filters, including "Broadcast band rejection filter", i.e. a high pass filter. Prices are in the USD 70-150 range - the more expensive ones allow DC to pass through the filter. The web site does not indicate whether customers requirements are met. I've bought a few preamps from Kiwa in the past, and I've also had a receiver modified there. The proprietor Craig Siegenthaler does an excellent job.
Apart from these two, I was advised about Rescue Electronics, which offers low pass filters for the DX-er. However, after the initial positive contact, I did not hear from the company again, not even after a follow-up email.
Are there designs out there that the hobbyist can use to make his own filter? Please use the comment field to share your ideas.
Conventional receivers often had a tracking preselector which helped attenuating signals outside of its passband. Older receivers more often used a manual preselector. With the advent of software defined radios, capable of recording from 192 kHz up to 4 MHz, a preselector loses its relevance. Some SDRs are "wide open", while others use a set of bandpass filters. The RF Space NetSDR for instance uses 10 sub-octave filters. The Winradio G33DDC has14 configurable bandpass filters. The Afedri SDR-net on the other side has none, while the G31DDC has a selectable high pass filter to reduce MW interference on SW.
My 100 kHz notch filter was designed by Swedish DX-er Stefan Wikander, is easy to build and was later refined by Dallas Lankford who added a 500 kHz high pass filter to the design. Read more here.
When it comes to high pass and low pass filters, there is a limited amount of off-the-shelf products. Tracey Gardner kindly directed me to the Minicircuits range of filters. Unfortunately, almost all their products are aimed at higher frequency ranges, but they have some interesting low pass filters. For the MW DX-er, the 1.9 MHz filter could be very suitable. In addition, the filters are very small with a female BNC on one end and a male BNC on the other. At around USD 35, they are quite inexpensive, too.
Other than that, it seems that you have to rely on small, dedicated enterprises. They will charge you more, but the products can be tailor-made for you, and quality will be excellent. Here are a couple of interesting manufacturers:
Clifton Laboratories offer active antennas, amplifiers, filters and other items of interest for the DX-er and radio amateur. The proprietor Jack Smith makes bandpass filters, band rejection filters, high pass filters and low pass filters with superb characteristics. They can be built to meet customers requirements. The price range is USD 40-70, metal cased with connectors. More details on their web page. My low pass filter was bought (un-boxed) from Clifton Laboriatories.
Kiwa Electronics has been around for decades. Kiwa offers a wide range of low pass filters, including "Broadcast band rejection filter", i.e. a high pass filter. Prices are in the USD 70-150 range - the more expensive ones allow DC to pass through the filter. The web site does not indicate whether customers requirements are met. I've bought a few preamps from Kiwa in the past, and I've also had a receiver modified there. The proprietor Craig Siegenthaler does an excellent job.
Apart from these two, I was advised about Rescue Electronics, which offers low pass filters for the DX-er. However, after the initial positive contact, I did not hear from the company again, not even after a follow-up email.
Are there designs out there that the hobbyist can use to make his own filter? Please use the comment field to share your ideas.
Thursday, July 05, 2012
The Afedri SDR-net - The Effects Of A Low Pass Filter
Those who have read my impressions of the Afedri SDR-net, will know that the receiver is susceptible to overloading, due to its modest 12-bit ADC and lack of band pass filters. Hence, in many cases one will have to reduce the internal VGA gain, which again reduces useable sensitivity.
While a bank of band pass filters would be the best solution, the second best is making or buying a filter which eliminates the strong signals - if they are away from the spectrum you want to monitor. I decided to test a low pass filter, so I could eliminate SW signals while listening to MW. I ordered a tailor-made filter from Clifton Laboratories, with a cut-off frequency of 2100 kHz.
I put it together today, and you can see the results below. The Afedri had been set up with max VGA gain, but I had reduced the gain by 10 dB in SDR-Radio. Still, I would have a sensitivity of around -104 dBm. The pictures show how the MW spectrum displayed before, and after I engaged the low pass filter. Not only was there a visual difference, the audible difference was huge.
In addition to the low pass filter, I also used a combined high pass filter (cut-off frequency 500 kHz) and 100 kHz notch filter, designed and built by Dallas Lankford. There is only one major LF source though, the 250 kW Loran C station on 100 kHz, 14 km away. I didn't do any before-and-after test of this filter, since removing it will kill MW reception regardless of receiver.
I probably should have reduced the Afedri's VGA gain another 3-5 dB, but I suppose you get the picture, so to speak. A quick check of the 49 meter band showed that there were no signals left, while before the signal levels were very high indeed.
I carried out the test with a 30 meter longwire and a 25 meter long coax feed line.
While a bank of band pass filters would be the best solution, the second best is making or buying a filter which eliminates the strong signals - if they are away from the spectrum you want to monitor. I decided to test a low pass filter, so I could eliminate SW signals while listening to MW. I ordered a tailor-made filter from Clifton Laboratories, with a cut-off frequency of 2100 kHz.
I put it together today, and you can see the results below. The Afedri had been set up with max VGA gain, but I had reduced the gain by 10 dB in SDR-Radio. Still, I would have a sensitivity of around -104 dBm. The pictures show how the MW spectrum displayed before, and after I engaged the low pass filter. Not only was there a visual difference, the audible difference was huge.
In addition to the low pass filter, I also used a combined high pass filter (cut-off frequency 500 kHz) and 100 kHz notch filter, designed and built by Dallas Lankford. There is only one major LF source though, the 250 kW Loran C station on 100 kHz, 14 km away. I didn't do any before-and-after test of this filter, since removing it will kill MW reception regardless of receiver.
 |
| MW spectrum no low pass filter |
 |
| MW Spectrum with low pass filter |
I carried out the test with a 30 meter longwire and a 25 meter long coax feed line.
Saturday, June 16, 2012
Afedri SDR-Net - Better Than Anticipated?
The screendump below is from the 31 meter band with rather high signal levels. I am running the Afedri at +24 dB VGA, which equals around -104 dBm sensitivity. At this VGA setting it's in fact a tad more sensitive than the NetSDR, yet there is no indication on the waterfalls of any overload. Very cool. This may indicate that the Afedri will perform well during the coming autumn's MW openings.
Earlier today I also did a recording test, with both SDRs recording 1250 kHz into an internal hard drive simultaneously. No hiccups or stuttering, and very low CPU. Maybe the Ethernet connection makes it easier for the CPU and that the network board does some or most of the processing. I don't know, but what I do know is that when you record from USB based SDRs stuttering may often be a problem.
Two Net-based SDRs Playing Together
If you have a router or a switch, you can connect several net-based SDRs to one PC. And if you use SDR-Radio, which allows multiple instances of the program to run, you can operate them simultaneously. Since I have one RF Space NetSDR and one Afedri SDR-net I decided to test this. What is needed are different IP addresses for both (or all) SDRs, and different ports. I am no network geek so I had my portion of trial and error, but with the help of SdrNetSetup and disconnecting and reconnecting the Afedri I got both SDRs to play along. On the jpg below the Afedri identifies as "SDR-IP".
Both SDRs are displaying a 1250 kHz span, with little CPU load. Another interesting observation is that when the SDRs are tuned to the same frequency, their audio appear to be perfectly synchronized. There is not the slightest trace of echo or other audio artifacts. Diversity reception, anyone?
Both SDRs are displaying a 1250 kHz span, with little CPU load. Another interesting observation is that when the SDRs are tuned to the same frequency, their audio appear to be perfectly synchronized. There is not the slightest trace of echo or other audio artifacts. Diversity reception, anyone?
Sunday, May 27, 2012
The Afedri SDR-net - Second Looks
I had some time this weekend to check into the Afedri SDR-net further. My beverages and the QDFA are all down, so I used one of the QDFA loops (7 m high and 20 m wide) as a temporary ALA-100 loop. It has quite a bit of gain especially on the SW bands.
The Afedri SDR-net sports a 12-bit, 80 MHz ADC, in contrast to the Perseus and SDR-IQ which use 14-bit ADCs, and the QS1R, NetSDR and Excalibur series which use 16-bit ADCs. Apart from a 30 MHz low pass filter, there is no band pass filtering. All the SDRs above except the Excalibur G31DDC have band pass filtering. If you buy an Afedri SDR-net you will accept some compromises, and you will need to do some mitigation measures. The question is of course: Is it worth it.
The Afedri SDR-net is only the second amateur-grade SDR I know which can be connected to the PC via Ethernet, the other being the RF Space NetSDR which sells for USD 1400 (I consider the SDR-IP a commercial-grade SDR). Unlike the NetSDR though, the Afedri SDR-net can also use the more common USB connection. However, the USB connection limits the spectrum to 230 kHz (250 ksamples/s) while the Ethernet connection gives access to 1225 kHz (1333.33 ksamples/s). If you opt for the Ethernet connection (highly recommended), be sure to use a crossover Ethernet cable when you connect the SDR to the PC. A standard Ethernet cable should be used if you go via a router or a switch.
There are two ways to power the SDR. There is a 12.6 VDC input in front (and a DC jack is included), however the DC voltage can be anywhere from 7.5 to 15 V. The problem with the DC input is that another compromise – a switching DC/DC converter working on 930 kHz – will reduce MW performance. My recommendation is to use the micro-USB input for DC power. If so, you can choose to use one of the PC’s USB ports, or you can modify the USB cable to power the SDR from an external, linear 5VDC supply. The USB connection draws 470 mA. This is close to the 500 mA limit of a USB port, so you may want to keep the cable as short as possible. Some laptops are reported to deliver less than 500 mA.
As mentioned by Alex in a comment to this post, a root hub connector will deliver 500 mA, while other hub connectors may be limited in current. Hence, if you're unable to power up the Afedri SDR-net from one USB connector, it may help to try another.
Sensitivity is an important issue for MW DX-ers in quiet areas. I measured around -91 dBm on AM, 6 kHz bandwidth with a 400 Hz tone modulated by 30 %. Internal gain from its Variable Gain Amplifier was set at 14 dB (see below). This is around 10 dB lower sensitivity than the NetSDR. Although sufficient for many purposes, the Afedri SDR-net will not resolve the weakest signals. A Norton push-pull preamplifier, from Kiwa or other manufacturers, will be helpful in many instances if signal levels are low.
Another vital question related to sensitivity is: When does the ADC go into clipping? You can adjust the VGA gain of the Afedri from -10 dB to 35 dB. It is possible to tailor-suit the gain with the use of a small app inside the HDSDR program (which comes with the Afedri). Pushing it all the way up to 35 dB may not be a good idea unless you are certain that there are no strong signals around. In this setting, I got ADC overload by feeding one signal generator signal at -28 dBm signal outside of the received spectrum. Reducing the gain to 26 dB raised the overload threshold to -23 dBm, while at 14 dB the threshold came within a more acceptable -12 dBm. The G31DDC, also without bandpass filters, did not overload within the -8 dBm limit of my signal generator. Of course, one signal does not reflect "real life".
The -91 dBm sensitivity was measured at 14 dB VGA gain. In theory, sensitivity could be higher, but rarely in practical terms (at 35 dB VGA, sensitivity was measured to -106 dBm, at 26 dB it was -104 dBm).
Hence, external filtering will be necessary in most instances. A SW listener near strong MW stations will want a high pass filter to eliminate overload from MW. As for me, in many instances I can probably live with a 26 dB VGA setting, but I will invest in a low pass filter to eliminate the strongest SW station around here, Murmansk-5930. It is sometimes heard with signals above -10 dBm.
It’s a bit too early to make conclusions about the Afedri SDR-net. The Arctic nights are light, and signal levels low, making it difficult to judge how it will perform in real DX situations. My impression however, is that for the price it’s a very capable SDR, able to run with a variety of software. You should however buy or make high pass and/or low pass filters to avoid overloading the ADC. And you may need to use an external preamplifier if sensitivity becomes an issue. So, if you are willing to compromise: Yes, it's worth it.
The Afedri SDR-net sports a 12-bit, 80 MHz ADC, in contrast to the Perseus and SDR-IQ which use 14-bit ADCs, and the QS1R, NetSDR and Excalibur series which use 16-bit ADCs. Apart from a 30 MHz low pass filter, there is no band pass filtering. All the SDRs above except the Excalibur G31DDC have band pass filtering. If you buy an Afedri SDR-net you will accept some compromises, and you will need to do some mitigation measures. The question is of course: Is it worth it.
The Afedri SDR-net is only the second amateur-grade SDR I know which can be connected to the PC via Ethernet, the other being the RF Space NetSDR which sells for USD 1400 (I consider the SDR-IP a commercial-grade SDR). Unlike the NetSDR though, the Afedri SDR-net can also use the more common USB connection. However, the USB connection limits the spectrum to 230 kHz (250 ksamples/s) while the Ethernet connection gives access to 1225 kHz (1333.33 ksamples/s). If you opt for the Ethernet connection (highly recommended), be sure to use a crossover Ethernet cable when you connect the SDR to the PC. A standard Ethernet cable should be used if you go via a router or a switch.
There are two ways to power the SDR. There is a 12.6 VDC input in front (and a DC jack is included), however the DC voltage can be anywhere from 7.5 to 15 V. The problem with the DC input is that another compromise – a switching DC/DC converter working on 930 kHz – will reduce MW performance. My recommendation is to use the micro-USB input for DC power. If so, you can choose to use one of the PC’s USB ports, or you can modify the USB cable to power the SDR from an external, linear 5VDC supply. The USB connection draws 470 mA. This is close to the 500 mA limit of a USB port, so you may want to keep the cable as short as possible. Some laptops are reported to deliver less than 500 mA.
As mentioned by Alex in a comment to this post, a root hub connector will deliver 500 mA, while other hub connectors may be limited in current. Hence, if you're unable to power up the Afedri SDR-net from one USB connector, it may help to try another.
Sensitivity is an important issue for MW DX-ers in quiet areas. I measured around -91 dBm on AM, 6 kHz bandwidth with a 400 Hz tone modulated by 30 %. Internal gain from its Variable Gain Amplifier was set at 14 dB (see below). This is around 10 dB lower sensitivity than the NetSDR. Although sufficient for many purposes, the Afedri SDR-net will not resolve the weakest signals. A Norton push-pull preamplifier, from Kiwa or other manufacturers, will be helpful in many instances if signal levels are low.
Another vital question related to sensitivity is: When does the ADC go into clipping? You can adjust the VGA gain of the Afedri from -10 dB to 35 dB. It is possible to tailor-suit the gain with the use of a small app inside the HDSDR program (which comes with the Afedri). Pushing it all the way up to 35 dB may not be a good idea unless you are certain that there are no strong signals around. In this setting, I got ADC overload by feeding one signal generator signal at -28 dBm signal outside of the received spectrum. Reducing the gain to 26 dB raised the overload threshold to -23 dBm, while at 14 dB the threshold came within a more acceptable -12 dBm. The G31DDC, also without bandpass filters, did not overload within the -8 dBm limit of my signal generator. Of course, one signal does not reflect "real life".
The -91 dBm sensitivity was measured at 14 dB VGA gain. In theory, sensitivity could be higher, but rarely in practical terms (at 35 dB VGA, sensitivity was measured to -106 dBm, at 26 dB it was -104 dBm).
Hence, external filtering will be necessary in most instances. A SW listener near strong MW stations will want a high pass filter to eliminate overload from MW. As for me, in many instances I can probably live with a 26 dB VGA setting, but I will invest in a low pass filter to eliminate the strongest SW station around here, Murmansk-5930. It is sometimes heard with signals above -10 dBm.
It’s a bit too early to make conclusions about the Afedri SDR-net. The Arctic nights are light, and signal levels low, making it difficult to judge how it will perform in real DX situations. My impression however, is that for the price it’s a very capable SDR, able to run with a variety of software. You should however buy or make high pass and/or low pass filters to avoid overloading the ADC. And you may need to use an external preamplifier if sensitivity becomes an issue. So, if you are willing to compromise: Yes, it's worth it.
Friday, May 25, 2012
The Afedri SDR - First Looks
I thought the RF Space SDR-IQ was small, but that was until I saw the Afedri. The latter's footprint is actually smaller than the SDR-IQ's. For comparison, in the picture below it is sitting on top of the Perseus, itself not a mammoth radio.
I haven't had time to much more than getting it up and going, so details will have to wait. It was very much plug and play, actually. I opted for powering it through its 5V USB connection, thus minimizing RFI. And I chose the ethernet connection rather than the bandwidth-restricted USB interface.
Not only is it smaller than the SDR-IQ, it sells for half the price but still offers a 1250 kHz bandwidth compared to the SDR-IQ's 192 kHz. However, the USD 249 price tag suggests that the creator, Alex Trushkin, has had to make some compromises. Like a 12-bit ADC while other SDR makers use 14-bit or 16-bit, no bandpass filters, and somewhat restricted sensitivity.
Still, my first impression is that it's a very cabable SDR, and basically unbeatable at this price level. You can buy a Norton push-pull preamplifier and lowpass and/or highpass filters and still have cash left compared to an SDR-IQ. And the SDR-IQ will not record 1250 kHz, and will not connect to the ethernet.
The Afedri will run with many SDR programs, such as Winrad, Linrad and SDR-Radio.
More as it happens.
Not only is it smaller than the SDR-IQ, it sells for half the price but still offers a 1250 kHz bandwidth compared to the SDR-IQ's 192 kHz. However, the USD 249 price tag suggests that the creator, Alex Trushkin, has had to make some compromises. Like a 12-bit ADC while other SDR makers use 14-bit or 16-bit, no bandpass filters, and somewhat restricted sensitivity.
Still, my first impression is that it's a very cabable SDR, and basically unbeatable at this price level. You can buy a Norton push-pull preamplifier and lowpass and/or highpass filters and still have cash left compared to an SDR-IQ. And the SDR-IQ will not record 1250 kHz, and will not connect to the ethernet.
The Afedri will run with many SDR programs, such as Winrad, Linrad and SDR-Radio.
More as it happens.
Wednesday, May 09, 2012
Another SDR To Meet The Arctic Challenge
Many hobbyists design SDRs these days. The most promising I've seen so far is the AFEDRI SDR-Net, designed by 4Z5LV Alexander Trushkin. The latest version is not only able to cover the MW spectrum (1250 kHz bandwidth), but even has an ethernet connection! In other words, you can connect it to your router/switch, and access it with whatever PC is connected to your LAN. Just like the RF Space NetSDR.
The specs aren't out of this world, but neither is the price tag. It will be interesting to see how well it fares compared to my other SDRs, Perseus, NetSDR, Excalibur and Excalibur Pro.
I've just ordered one, and I hope to do some preliminary tests by the end of May. Thanks Tracey Gardner for alerting me.
 |
| Photo: 4Z5LV Alex |
I've just ordered one, and I hope to do some preliminary tests by the end of May. Thanks Tracey Gardner for alerting me.
Sunday, May 06, 2012
G39DDC Software For G31/G33 Files Playback
A good thing about Winradio's software is that you don't need the actual receiver. They load into a "Demo mode" if no receiver is connected. It is fully functional, and allows you to play back files without the receiver connected if you wish.
I never seriously considered purchasing the G39DDC Excelsior, but I was keen to check out the software, since it would likely have some improvements over the G31 and G33 software packages. It was a mixed bag.
The G39 software has many functions not found on the G31 and G33 software, mainly because it's supposed to support a scanner going up to 3.5 GHz. I had hoped to see a better designed playback function than those found on the G31 (mediocre) and G33 (improved). Indeed I did! The playback bar works very much like those found on the Perseus, Spectravue and SDR-Radio; you can click anywhere inside the bar and the recording will move to that spot instantly. Playing back a recording appears to be easier if you use the G39 software than if you use the G33 (and particularly the G31) software. However, there is still no way to make a small selection of the recording, and loop it. Both Perseus and SDR-Radio feature this very useful tool.
The last four lines on the G39 control box expands/subtracts by use of the tool box to the right of the file path.
Winradio G3x software has never been the easiest to use for those who want to check offsets from the nominal frequency. The G33 Demod window can be zoomed in to a width of 240 Hz. Maximizing the window enables the user to move in 1 Hz steps. However, the resolution is rather low so doing exact offset measurements isn't very easy. The G39 DDC2 window can only be zoomed to 500 Hz, but the resolution is better, so it is still possible to move in 1 Hz steps. Vertical lines on the display help a lot.
It would be nice though if there was a way to change the MHz labeling to kHz...
I never seriously considered purchasing the G39DDC Excelsior, but I was keen to check out the software, since it would likely have some improvements over the G31 and G33 software packages. It was a mixed bag.
 |
| G39 in Waterfall mode playing back a G33 LF recording |
 |
| G33 recording/playback controls |
 |
| G39 recording/playback controls |
 |
| G39 DDC2 window |
It would be nice though if there was a way to change the MHz labeling to kHz...
Sunday, February 12, 2012
Kongsfjord Mid-Winter Report
Today was my first visit to Kongsfjord in 2012! Checking antennas and replacing the QDFA battery was long overdue, with weather being the limiting factor. Last weekend saw temperatures down to -25 Celsius and winds up to 25 meters per second. The result is razor-sharp ice particles blowing around. You don't want to work outside in conditions like that. The picture below from Kongsfjord International Scuba School (copyright) should illustrate my point. My house is just outside the left frame.
Today though was mild and relatively calm, allowing me to replace the last beverage lamp cord feedline with a Belden Twinax. Works fine.
The QDFA inspection was rather disappointing. One of the clamps securing the secondary fiber glass rods had snapped, probably as a result of the temperature and wind. Also, two of the loop wires had snapped, probably of the same reason. Lesson learned is that we need more durable wires for our QDFA. And another example of the mechanical challenges loop arrays are in areas with extreme weather conditions and without being able to look after the array on a daily basis. But we live and learn! Maybe next season the QDFA will be operational all winter!
Today though was mild and relatively calm, allowing me to replace the last beverage lamp cord feedline with a Belden Twinax. Works fine.
Subscribe to:
Posts (Atom)