Thursday, September 27, 2012

Update: Sensitivity Measurements

Some time ago I published some sensitivity measurements from receivers I have owned or borrowed. It's been a while since the last update, but here it is.

Saturday, September 22, 2012

The Mini-Whip - Erecting It And Initial Results

Although I have used the Mini-Whip before, this is the first time I've erected it properly, and made a systematic test and comparison with my other antennas.

I decided to mount the Mini-Whip to a 21-ft telescoping fiber glass mast from Max-Gain. The mast costs a lot more than the antenna, but is extremely robust. The elements are hollow, allowing the feed line to run inside the mast. I secured the antenna with Coax-Seal at the top.
 Of course, the fiber glass mast needs a support, so I basically used what was at hand.

Identical masts have been in use for two winters in the QDFA array, and I don't expect it to collapse or break.

At the bottom of the mast I made extra room for the feedline to avoid stress and potential damage.

On to the tests! Comparing a small, unidirectional active antenna with directive beverages from 225 to 500 meters long is a bit like comparing a family sedan with a racing car - and half expecting the former to win. And just so it's said: On Shortwave the Mini-Whip outperformed all my other antennas with a comfortable margin. But what about Mediumwave?

The first test array was comparing signal levels on the groundwave stations audible here. I compared the Mini-Whip with the QDFA phased array, and the 310 degrees beverage (225 meters). The stations were: 153 kHz NRK Ingøy, 399 kHz NDB "BV", 657 kHz Radio Rossii Murmansk, 675 kHz NRK Røst, 1134 kHz Radio Mayak Murmansk, 1449 kHz Radio Mayak Monchegorsk and 1521 kHz Radio Mayak Zapolyarny.

And this is how it turned out:
310 beverage
-80 dBm
-61 dBm
-70 dBm
-82 dBm
-60 dBm
-57 dBm
-73 dBm
-72 dBm
-56 dBm
-112 dBm
-103 dBm
-96 dBm
-83 dBm
-71 dBm
-63 dBm
-79 dBm
-75 dBm
-70 dBm
-72 dBm
-69 dBm
-60 dBm

10-20 dB behind the 310 isn't bad at all, and almost equal levels with the QDFA at times. I did expect it to fare better on LW though, given its reputation as an excellent antenna for NDB hunting.

One important factor I have missed in this test however is that the other antennas have preamps in front, while the Mini-Whip has none (except the one in the Power Feed Unit).

Because of this, I did a quick measurement of each antenna's noise floor at current conditions. The Mini-Whip measured -112 dBm (1200 kHz, daylight), while the beverages were around -118 dBm. All measurements were done with the G33DDC Excalibur Pro.

Skywave tests have been postponed to a later weekend.

Friday, September 21, 2012

Right In The Middle Of The Aurora...

This doesn't look too promising. In fact, the MW was all Arabic and Farsi this evening - with a couple of exceptions, like this one from Down Under. We'll see what happens during the night and tomorrow morning.

Sunday, September 16, 2012

Weekend DX - Not Much More To Tell

Last night's DX - or should I say this morning's DX - was uneventful. Only the usual stations were heard during the one full hour I recorded, and the level of European stations were surprisingly high so a lot of frequencies were pested with noise. Iowa/North Dakota/Wisconsin stations were dominating, indicative of disturbed propagation.

Exceptional rain fall last night after an exceptionally mild September day - up to 13 Celsius. Still nice and mild with 9 Celsius, and dry.

Saturday, September 15, 2012

Weekend DX - And How Does The Afedri SDR-net Cope?

I drove to Kongsfjord Friday afternoon to do further tests of the 340 (alas, jury's still out and I don't know when it will return - if at all), and do some DX. Australia's been going quite well for several days, however for some reason only South Australia. The rest of the country is mostly absent, even the most common of them all, 4QD-1548. X-band has been exceptionally quiet.

Radio National 729 and 5AN 891, both in Adelaide, have had very nice signals, such as this one recorded at 17:30 UTC on 729 kHz. It was recorded off the Afedri SDR-net.

Conditions towards North America last night were mediocre, but enough to make a comparison of the dual 340 beverage, compared to two single 340's. A dual beverage has definitely more gain than a single one - average measurements suggests 5-6 dB or one S-unit. But it is more susceptible to Loran C noise too, and the F/B ratio has not been improved. It was impossible to measure if the front lobe had become narrower, which is basically the idea behind the dual beverage.

Some time ago I promised to get back to the Afedri SDR-net's capacity as a MW DX receiver. Could it really stack up with the much more expensive SDRs like the G33DDC, Perseus and NetSDR? Well yes it can. If I pay a bit attention to its somewhat fragile front-end, and reduce the VGA gain when necessary, there isn't much the other SDRs can do that the Afedri can't. It's a keeper. It has been appointed official DU hunter, and is connected to the 500 meter 50 degrees beverage.

I'm writing this Saturday evening, hoping to hear some North Americans tomorrow morning. Next weekend will see the inauguration of Bakker's MINI-whip to the MAX-Gain (21 ft) mast which was ordered a few days ago.

While waiting, I'm enjoying "Luftgitar" (Air Guitar in English), a rock program  on RAS-2 - via satellite of course.

Monday, September 10, 2012

Season Preparations With OJ - Final Day

Sunday was typical autumn - brisk winds and showers, and temperatures around 6-7 Celsius. Luckily, most of our outdoor work was done by then.

Testing the dual parallel beverage wasn't easy. We needed signals from many directions to be able to determine if it had other - and hopefully better - properties than a standard beverage. Stable MW signals are mostly only found to the southeast (Kola peninsula), so we settled for a suite of NDBs in the 300-400 kHz range.

The tests were inconclusive. We understand that in order for a dual parallel beverage to work properly, the two beverages need to be identical. Terrain conditions prevented this. More surprising though, is that the eastern leg provided significantly better gain than the western leg, from 2 dB up to around 5 dB. So in electrical terms, they weren't identical.

The two connected together via the DX Engineering Combiner did add 5-6 dB of gain over the single eastern beverage. Unfortunately, this level of gain also a substantial increase in broadband Loran C noise. This seems to be the limiting factor, despite using a 75 dB 100 kHz notch filter and a high pass filter for protection.

I will continue testing the 340 dual parallel beverage next weekend, weather permitting, hopefully with skywave signals. We will then find out if we will keep the dual beverage (not very likely), or which of the eastern or western single beverages will be kept.

We drove to Vadsø in the afternoon. The weekend's last dinner was woked fillets of chicken with leak, paprika, red chili and jasmine rice with curry. Lotsa curry. The remaining wine bottle from the weekend was a 2008 Rossodiverzella. Very good. For dessert: Mövenpick vanilla ice cream with chocolate syrup or raspberry sauce.

Conditions improved during Sunday, and in the evening OJ logged two most wanted Australians on 729 and 891 kHz on the 50 degrees beverage.

OJ left Vadsø at 0415 UTC on Monday morning, and I'm preparing for work with a moderately aching back...

Sunday, September 09, 2012

Season Preparations With OJ - Third Day

Saturday was relatively calm, cloudy most of the day but sunny and nice towards the afternoon. The dual, parallel 340 degree beverage was finally completed, and briefly tested.

The QDFA refurb was completed as well, and performed to specs when we tested it. This is what we did: First we connected loop no 1 directly to the feed line while monitoring two groundwave stations from Murmansk; 657 and 1134. Those stations are located at 142 degrees, or roughly South-East of here. Although not in the QDFA's deepest null, the loop should attenuate their signals somewhat. 

After testing loop no 1 we removed it and connected loop no 2 etc. When we had recorded the signal levels for each individual loop, we connected all loops to the phaser and feed line.

The individual loops received 657 kHz at an average level of -70.7 dBm (ranging from -69.3 to -72.4). The QDFA received 657 at -88 dBm, giving roughly 17 dB of attenuation.

1134 kHz levels were - 85.6 dBm in average, ranging from -83 to -87.5. The QDFA level was -94 dBm, or 8.4 dBm attenuation. We are quite satisfied with this.

It should be mentioned too, that the phaser box escaped the previous, rather harsh winter, unscathed. Everything appears to be working, thanks to the continuing modification work carried out by Dallas Lankford. It now appears to have passed the weather test of one of the worst habitable winter climates of the world. It is also worth mentioning that the fiber glass masts from Max-Gain are exceptionally robust.

Our backs were aching after two challenging days on the antenna field, but in the evening we could finally enjoy reindeer sirloins with mashed potatoes and woked leak, red onions, red chili and (red) tomatoes. A most delicious Australian red wine was enjoyed with the meat, 2010 Miss Harry bought in Finland (and recommended by Antti Altonen). It's in fact not available in Norway.

Dessert: Jelly with artificial strawberry taste, and (real) vanilla custard.

Saturday, September 08, 2012

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...

Friday, September 07, 2012

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.

Saturday, September 01, 2012

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.