Season Preparations with OJ - Second Day

Friday was a bit windy but dry and even a bit of sun, so all in all a nice day for antenna maintenance.

The QDFA was in need a total refurbishment, except the superb Max-Gain supports. New antenna wires were fitted, resistors replaced, transformers reworked and feed lines repaired. The feed lines will be set up today, allowing us to test the QDFA with a fresh battery.

The dual, parallel 340 degree beverage feed line system was built, including transformers, isolators and a combiner, including grounding. The western part of the beverage was set up yesterday, the eastern part will be erected today.

We also erected the "old" 310 degree beverage. It apparently works very well indeed, since with the current auroral conditions stations from the Middle East were very strong to its back lobe.

After 8 hours more or less outdoor, walking, lifting and carrying (heavy loads) most of the time, we were quite exhausted in the evening. We did have enough energy though to make ourselves woked salmon with carbonara. We enjoyed Calles Riesling with the salmon, and we even found a bottle of port wine left over from last year's KONG21.

No transatlantic signals during the night.

Saturday morning is overcast but dry and relatively calm, and 6 degrees Celsius. It is soon time to get to work...

Season Preparations With OJ - First Day

OJ Sagdahl arrived to Vadso by plane on Thursday, and we drove the 170 km to Kongsfjord in the afternoon in rainy and windy conditions. Our goal is to get all or most of the antennas out, including the new dual parallel 340 degrees phased beverage. The 50 degrees beverage was erected last weekend and is the only one up at the moment.

Some Japanese stations were heard in the afternoon, but all of a sudden everything disappeared - the ionosphere is obviously still "shaken" after the CME and proton event a few days ago. Later in the evening we heard a few Filipinos.

Prior to and half an hour after sunrise this Friday morning, South America had decent signals on the back lobe of the 50 degrees beverage. Mostly Brazil, and a few from Argentina and Uruguay. Such as Radio Monte Carlo, Montevideo on 930.

As usual when DX-ers come together in Kongsfjord, good food is prepared and good wine is consumed. Thursday evening we put together a reindeer stew, comprised of thin reindeer shavings, red onion, red chili and mashed potatoes. A 2006 Weinert Carrascal proved to be a superb companion. We had chocolate pudding with vanilla custard for dessert, and we finished off with a glass of Disaronno. Or maybe two.

Photos will follow.

A Cool Recorder For The Afedri SDR-net

All the SDR software packages supporting the Afedri SDR-net can do RF recordings, and to a varying degree scheduling is possible too. But if the main purpose is recording and not live listening, you might find yourself wanting just a simple recorder. Well, the Perseus SDR has its Mestor, and now the Afedri SDR-net has its Afedrec! It was developed by Vasiliy Gokoyev and made available through the Afedri SDR-net Yahoo reflector.

Afedrec is a character based application, and at that it takes some time to put all the parameters in (and to avoid the syntax errors). Looking for a way to make a one-click recording, I turned to my old friend System Scheduler which had proved to be a very reliable application for doing G31DDC scheduled recordings.

Afedrec in the CMD window. Each dot represents 10 MB of data.

This turned out to be a very good idea indeed. Programming System Scheduler to make recordings of various lengths (or various center frequencies or various sample rates) is quite straightforward. When I open System Scheduler, I can select the recording I want to make, and select the Play button. Of course, I can also set up automated scheduled recordings.

Programming the Afedrec

When Afedrec is recording, you can play back previous recordings with Spectravue. Apparently this is not possible with SDR-Radio, because it holds a UDP socket open and by default the second connection is not allowed.

Afedrec is extremely gentle on the CPU. On my i5-2310 2.9 GHz system, the CPU load when running at 1333 kHz sample rate is 1 % or less, while SDR-Radio and Spectravue both use around 7 % CPU. Afedrec recordings can be played back on SDR-Radio, Spectravue, Winrad and HDSDR.

If you want to do scheduled recordings with the Afedri SDR-net, or a one-off recording without monitoring (for instance a full hour recording), the Afedrec/System Scheduler combination is hard to beat.

Preparations For The Upcoming Season

With the second weekend without the midnight sun, evenings are already becoming darker. Although it will still be three weeks until we can expect to hear any DX, preparations start early.

We are always experimenting with new antennas. This year we will test a replacement to the 340-degree beverage, namely a staggered beverage in roughly the same direction. Otherwise, the antenna farm will not change much.

Most of the time was spent indoor though, painting walls that haven't seen new paint since the mid-70's. The photos below were taken just after sunset on Friday. It is the northern side of the Veines peninsula. This is quickly eroding (in geological perspective) sand stone.

Take Your SDR To The Beach

Getting away from man-made noise has become increasingly important for DX-ers - and increasingly difficult. Going to the seaside or into the mountains can provide excellent opportunities for DX. But you need power! A laptop can last a night if one brings along an extra battery. However, feeding a 5V SDR from the laptop will either not work at all (too much current load), or it will drain the laptop's battery rather fast.

Battery packs have been around for a while. Some of them are quite powerful. After a quick search on Ebay I ordered a 11200 mAh battery pack which has two 5V outputs, rated at 1A and 2.1A. It came with a variety of adapters and connectors so one should have no problems to charge any mobile phone on the market today.

No, you can't power an R-390A with it... 

Left and right: 5V outputs. Middle above: DC input. Middle below: LED lamp

But the battery pack can do more than to give extra juice to demanding smartphones. The one I bought can power two SDRs! The Perseus draws around 750 mA while the Afedri has a modest 390 mA demand. At least in theory, this battery pack will power the Perseus almost 15 hours, and the Afedri almost 29 hours.

I don't know how much current is necessary to run the NetSDR - probably a bit more than the Perseus but less than 1A since I could feed all three of my 5V SDRs from the 1A output.

Before connecting the battery pack to my SDRs I checked the voltage of the DC outputs. I was somewhat surprised to see that they weren't quite the same. The 2.1A output measured 4.95V which is very good, while the 1A output measured 5.35V. That's a bit on the high side. Although all three SDRs worked with 5.35V when I tested them, I have decided not to push my luck. I'll stick to the 2.1A, 4.95V output.

Otherwise, the battery pack is a nice looking, small and light device.  The enclosure had FCC and CE logos on it, hopefully for a reason, and the price was USD 40 including air mail shipping from China. And they've even built a LED torch light into it. So you can search for the car keys you dropped when you erected the antenna.

Update Aug 11:
I let the battery pack feed the Perseus for most of yesterday, until only the last of the indicator LEDs were lit. How much juice was left I don't know. I was expecting (or fearing) that voltage would drop as the battery drained. However, the voltage reading of the 1A output was identical (4.95V) to the voltage when the battery was fully charged. So apparently, the battery is able to keep voltage stable for a very long time.

Thank you Takashi Kuroda for making me aware of these devices.

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.

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.

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.

MW spectrum no low pass filter

MW Spectrum with low pass filter

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.

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?