The Nooelec 50 kHz - 150 MHz 20-dB LNA

I ordered it because the Fobos SDR I was using had pretty mediocre sensitivity, and I wanted to see if a preamp could increase it a bit. The Fobos had other issues too, so I ended up returning it. But I think the Nooelec will come in handy when FM season kicks off next May.

At KONG HQ, we’re no strangers to preamps. We need to split each of our signals to three users using MiniCircuits 8-port passive splitters. Sometimes, the MW band signals are so weak that preamplification actually makes a difference.

However, many DX-ers deal with high noise floors where a preamp won’t help and might even overload the receiver. So, it’s a bit of a mixed bag.

Anyway, I was curious to see how it performs on the SW bands.

This device is tiny compared to what we’re used to, like this 16-dB preamp from DX-Engineering!

Nooelec LNA vs. DX-Engineering RPA-2

So, it’s got SMA ports on both the input and output. You power it with a 5VDC supply through a Micro-USB port. Honestly, it might be a good idea to switch to the more common USB-C port soon.

For this quick test, I set up a Perseus22 with a center frequency of 15 MHz, which lets me receive from 14.2 to 15.8 MHz. I picked 15290 kHz kind of by chance - NHK World Radio was broadcasting in Japanese from the Issoudur transmitter in France at that time. I used a 5-meter high, 20-meter long sloping L-antenna, which worked great. The LNA was powered by a battery bank

So, this is what the spectrum and waterfall looked like before I hooked up the LNA.

The noise floor is around -120 dBm, with signal levels hitting just at or below -70 dBm. When I turned on the LNA, here’s what happened

The noise floor has gone up to about -100 dBm, and the peak signal levels are just below -50 dBm, which matches the 2.5 dB loss the manufacturer mentioned. The 27-dB gain increase on 15290 is because of random and quick signal level changes. We do see a few more signals on the waterfall that might be clearer with the LNA, but there’s also more noise. So, in this test, the LNA likely didn’t help with signal recovery. With a lower noise floor, it might make a difference.

I spent about  USD 35 on the device and another $12 for the slow USPS shipping. Right now, the RPA-2 HF Preamplifier from DX-Engineering (shown above) is priced at USD 270. It’s definitely more versatile. But it makes you wonder: Could we do with less?

The KONG HQ is Ready (Almost)

 I did some antenna work this and last weekend, along with SDR testing. Last weekend I rolled out the 50-degrees beverage antenna in sunshine and 20 Celsius. Not quite high today, but 15 Celsius is still warm for 1st September. Cloudy and a little breezy. Having spotted no reindeer, I elevated the 50-degrees beverage to an average of 130 cm. I also rolled out the 310 degrees beverage, which points roughly towards Chicago. It has an average height of around 200 cm.

"Far end" of the 50-degrees beverage

"Looking home" towards the feedline of the 310-degrees beverage

What remains to do is to deploy the staggered 340-degrees beverage, and to ground and elevate the 80-degrees beverage.

Perseus22 testing continues. Phasing the 50 and 80 beverage wasn't a good idea, they were too close in performance. I have now replaced the 80 with the newly erected 310 for a better difference in directivity. And finally, one for the food lovers:

Junipers! Not often ripe at this latitude. Great for flavouring reindeer and lamb meat

The RigExpert Fobos SDR

New SDRs do not come very often, so they are usually worthwhile to check out. The Fobos SDR from RigExpert in Ukraine looked like a novel design with promising features. I got it a little over two weeks ago, and my first impressions did leave some question marks. You can read the blogpost here.

Further testing unfortunately lead to a negative conclusion. This is not the SDR you should buy. At least in its current configuration.

And here is why.

Fobos SDR Is Here! But There Is a Catch...

 Arrived last Friday. The Sunday before I had brought the signal generator with me from the KONG HQ in anticipation of its arrival, since it was unlikely that I could go there this weekend for testing. A 10k run on Saturday got all the attention (and rightly so since I did a PB on the run).

Its blue box with yellow elements such as the five SMA connectors creates a nice tribute to its Ukrainian heritage.

Anyway: I have tested the device. Installation was almost as straight-forward as I expected. I have tested the Fobos SDR with HDSDR 2.80 and 2.81 beta 6, and SDR# (version 1716). It weighs in at 143 grams. Less than one-tenth of the 2-MHz Perseus22.

A few pictures follow. I wonder how they're going to open the box if they need to service it. There is nothing for a screwdriver or torxdriver to connect to. "No serviceable parts inside"?

I should have checked the block diagram more carefully before I bought it.  I was quite surprised that sensitivity on the HF1 and HF2 antenna inputs is pedestrian, to say the least. I measured around -85 dBm on 1000 kHz, actually up to 20 dB worse than other SDRs I have! Now, the block diagram indicates that the LNA only activates in "RF mode", i.e. from 25 MHz and up. So, there is no amplification in the <25 MHz (HF1/HF2) range except the LTC6401 chip.

So, that's where the LNA is hiding

What a strange omission. And why on earth didn't I notice.

It does sample 50 MHz. But the lowest sampling rate is 8 MSPS, not 4 as indicated on their web page. They need to offer lower bandwidths as well. 

It is very light on CPU. Sampling 50 MHz was handled with ease on my four years old HP AMD PC. Recording 50 MHz - well I'm not sure that it was stutter-free, but it didn't crash the application or the PC.

It is quite warm to touch when sampling 50 MHz. 8 MHz was a lot cooler.

Here at home I have no antennas, so it's really quite limited what I can do. And I really need to talk to the people at RigExpert about this. Hopefully, one of the coming weekends I will be able to test how it performs on FM at the KONG HQ, compared with the RSPdx.

More as it happens.

RigExpert FobosSDR

 After some delays over the summer, the FobosSDR from Ukranian company RigExpert is now available. I just ordered mine from wimo.de for EUR 415 (export). GigaParts in Tennessee wants USD 390, but is out of stock as I write this. With a 14-bit ADC resolution, up to 50 MHz sampling rate and two channel direct sampling on the frequency range below 25 MHz, this one may be a very interesting addition to the SDR world. Oh, and it tunes up to 6 GHz. Hardly of interest to the MW DX-er, but there you are.

We will see! When it arrives!

More on the Perseus22 (And a Foggy KONG HQ)

With version 1.2 of the Perseus software out I was hoping to see the implementation of some essential functions for the MW DX-er. However, it was mostly fixes and improvements. I did have a chance to test the WRTH database though. While connection and loading of the database was instant, the results were underwhelming. It seems to me that the WRTH database is far from accurate. One of several examples on the 19-metre band (the only band I checked) is shown below. No it's not Radio Habana Cuba, it's the Voice of America.

Also, MW stations are not listed at all.

There are many databases available. For MW DX-ers a regionally filtered version of MWList would be a lot better. For SW DX-ers I suppose anything but WRTH is better. Sorry to say.

Below is the business end of the Perseus22, namely the back panel. The SMA to BNC pigtails on HF1 and HF2 are tailor-made from Bonito in Germany.

The four channel windows are adjustable in height and width and can be moved around. Below are three of them, HF1, HF2 and VHF1 (the DAB+ band).

After a wet and rather chilly June, we've had dry and warm weather this summer. Coastal areas are exposed to fog though, and yesterday evening it was "thick as peasoup" as we say here. The KONG HQ seen from the beach, 60 metres away.

Perseus22: Increase your hard drive budget

The IQ files from the Perseus22 are proprietary, with the extension p22. So you can't read its properties like you can with a wav file. Since I thought the megabytes added up rather fast, I decided to find out exactly how much.

If you record one channel only, the IQ file will increase with roughly 15 MB per second.  If however  you record two channels (HF1 & 2, or VHF1 & 2), it will double. Which is quite natural. So, we're talking around 30 MB per second, or 108 GB per hour.

Compared to the original Perseus, which also records IQ files off a 2 MSPS range, it only uses around 7.5 MB per second. More exact: 61,000 bps. Now, Perseus recordings are 16-bit, so I'm quite confident that the Perseus22 is using 32-bit recordings.

Now, isn't a 32-bit recording better than a 16-bit? In theory, yes. In real life, no. Several years ago I spent quite a few hours comparing 32-bit recordings from the Winradio G33DDC with Perseus recordings. It was impossible to tell the difference.

It would be nice if Microtelecom/Elad made 16-bit recordings optional in a software update.

Perseus22 - Evaluation

So, after having tested the Perseus22 to the best of my abilities, I did a 10-page evaluation based on its current software version 1.1. Although it must be regarded as a rather unfinished product, at least with regards to parts of the software, it shines in other areas, like nulling and enhancing signals, not only in live mode but from IQ recordings as well. I spent a few hours testing it out, and it didn't disappoint! Report is here.

Enjoy!

Perseus22 - Skins

Which program was the first to use "skins"? Winamp? People have different preferences with regards to how they want their software to display on the monitor. Perseus22 offers three variations; User, Army and Hewlett. In addition, the "User" skin is configurable beyond belief - so instead of "skins" maybe Perseus22 should have offered a suite of "Styles". The current default skin looks good, but suffers from small fonts and unsatisfactory contrast. Especially as age has taken its toll on vision. And admit it: Which 20-year old will buy a Perseus22?

Anyway, below are the three skins currently (July 2024) available in Perseus22:

Default "User"

"Army"

"Hewlett"

If of interest, the three images were made when I had two antennas connected to the HF ports, one (left) sampling the 19-metre band and the other sampling the 31-metre band.

 

Perseus22 - DAB

 Back at the KONG HQ after a couple of weekends spent running! First, Midnight Sun Marathon in Tromsø on June 22 doing a half-marathon that exceeded my expectations. A week later I attempted a Backyard Ultra in Kirkenes, near the Russian border, where I bailed out after six rounds and 40 km. Thighs still aching.

 Now: Vacation! So, I thought I'd connect my FM antenna, pointing perpendicular to the DAB transmitter in Kongsfjord, to the Perseus22. No problem. The DAB transmitter is only 4 km away and 100 watts.The only available MUX here is the NRK MUX, comprising 18 channels including my favourite NRK P13. The screen dump below shows how DAB+ is received. Indeed, I have my doubts if legacy DAB is decodeable, as the manual specifically mentions DAB+ and not DAB. As far as I know, legacy DAB is only available in the United Kingdom now. Maybe someone in the UK could confirm.

With the "Snap DAB Freq" option selected, one can move from MUX to MUX by scrolling the mouse up or down. No keyboard up/down entries available in version 1.1.

No program info (show, artist, title, image/logo) is available in this version, unless I have overlooked something. Channel selection is excellent, instant decode.