Category Archives: Software Defined Radio

Ivan compares the AirSpy HF+ to the KiwiSDR

Many thanks to SWLing Post contributor, Ivan (NO2CW), who writes:

I have been running a public Kiwisdr server for a while and yesterday decided to plug in the new Airspy HF + into the same antenna for a side to side comparison. The antenna is an 80m dipole and the test was done during local afternoon, around 3 PM. I did not use any of the many new noise reduction features that are incorporated into both SDR Console 3 and the SDR web server. The 11 minute video is located here:

Click here to view on YouTube.

When I have the time I will run a similar test in nighttime conditions and also test the Airspy HF+ against a few other radios sitting on my desk.

Thank you for sharing this, Ivan!

Addendum: More Notes on the HF+ SDR on Medium Wave & Long Wave

In my recent post on the AirSpy HF+ vs Elad FDM-S2, I commented on medium wave reception only.

This past weekend I swapped out the Wellbrook ALA1530S+ for another Wellbrook loop, the ALA1530LN Pro. This LN Pro model is less likely to overload receivers at my suburban Tacoma, WA location. Both AirSpy and Elad radios performed admirably with the LN Pro and it was nearly impossible to find any reception differences on medium wave.

Before the antenna swap though I experimented with inline attenuation modules (“bullets”), typically used in cable TV installations. I used the same sample rates on the SDRs as described in the previous article. After some tests with different attenuation levels, I came to the following conclusions during daytime comparisons:

FDM-S2 with ALA1530S+ loop, medium wave: needs a minimum of 6 dB attenuation to avoid overloading. Anything less causes saturation of the spectrum & waterfall, “crunching” overload noises, and minimal or no received signal.

HF+ with ALA1530S+ loop, medium wave: I had to search diligently to find any signs of false signals or overloading, but finally noticed a weak image or spur of a S-9+60 dB (-13.5 dBm) local station on 1560 that was appearing very weakly on 1270 kHz, mixing with the station on that frequency. Sometimes it was there, other times the spur or image would drop down and disappear, leaving the 1270 signal alone. If I added just 3 dB of attenuation in the antenna’s feed line, the interference from the 1560 station was gone for good. The S-9+60 dB station is a very strong signal; it’s impressive that the AirSpy HF+ deals with this and similar powerhouse signals so well.

Long wave: Below are two screen captures from my local long wave reception in the evening, made moments apart with each receiver.



As you can tell, there are a half dozen or so additional signals seen on the HF+ below 200 kHz that do not appear on the FDM-S2. These extra spikes are images or spurs from medium wave signals that were missing from the FDM-S2’s reception–bravo Elad! However, the remaining spikes on both radios below 200 kHz seemed to be noise or interference.

Each receiver had roughly equal performance in the bulk of the long wave spectrum, when I did A-B comparisons on the same beacon signals. I’m not a LW or NDB DXer however, so I can’t claim any expertise on these frequencies. In short, though, both radios seem neck-and-neck from about 200 to 500 kHz.

The DXer of LW frequencies may want to look elsewhere for a better performing radio than either the FDM-S2 or HF+. SWLing Post reader Tudor Vedeanu has commented that the SDRPlay RSP1A  and the Eton E1 work very well at long wave.

Guy Atkins is a Sr. Graphic Designer for T-Mobile and lives near Seattle, Washington.  He’s a regular contributor to the SWLing Post.

Brief Medium Wave Tests of the HF+ and FDM-S2 SDRs in a Suburban Location

The AirSpy HF+ is the new SDR on the block, but how does it compare to the Elad FDM-S2 which is more than 2-1/2 times its $199 price? My main interest is finding out how they compare in a very RF-quiet DXpedition setting, but today I compared the two briefly from my home in Puyallup, Washington (near Seattle).

The receivers were connected via a two-way antenna splitter to the output of a Wellbrook ALA1530S+ loop antenna. I monitored during mid-afternoon local time to ensure that all my MW locals in my suburban location would be at full power, for the best test of the radios’ overload performance. The Wellbrook active antenna is rather “hot” and sometimes overloads receivers during the daytime unless attenuation is added to the signal chain.

I noted there were no truly weak medium wave signals available during the session so comparing sensitivity wasn’t appropriate. However, the band was full of strong daytime MW signals.

It became apparent quickly that the upstart HF+ provides strong competition to the Elad SDR. Clearly, the AirSpy’s trade-off is bandwidth for raw performance at lower cost–approx. 660 kHz alias-free coverage versus about 6 MHz maximum for the Elad.

Using the same center L.O. (local oscillator) frequency, short recordings were made with both receivers on the same receive frequency, same bandwidth, AGC setting, etc.  To approximate the 660 kHz coverage of the HF+, I set the FDM-S2 to its 768 kHz sampling rate, the closest available setting to 660 kHz wide coverage.

Here are the results on 1540 kHz, just 10 kHz away from a strong signal on 1550:

AirSpy HF+ – 1540 kHz

Elad FDM-S2 – 1540 kHz

What’s wrong with the above audio picture? The FDM-S2 is clearly overwhelmed by the strong RF on the upper end of the MW band. Visually, the spectrum looked like this with the Elad:

Elad FDM-S2 waterfall/spectrum (1540 kHz)

The noise floor rose by approximately 20 dB due to the overloading. The HF+ showed a normal waterfall and spectrum display while tuning 1540 kHz:

AirSpy HF+ waterfall/spectrum (1540 kHz)

Let’s listen to two more audio clips, this time from 720 kHz which is adjacent to very strong 710 KIRO, the ESPN affiliate in Seattle:

AirSpy HF+ – 720 kHz

Elad FDM-S2 – 720 kHz

This time the difference is subtle, but I think you’ll agree there is a greater amount of “crunchy” background distortion noise on the FDM-S2 recording. I found this to be the case in each instance where I compared receivers on frequencies adjacent to strong locals.

I no longer own a Perseus SDR, but that receiver handles the entire MW band at this location without overload using the same Wellbrook ALA1530S+ loop.

I’d like to emphasize that these were brief, somewhat casual AirSpy HF+ vs. Elad FDM-S2 tests. I expect that in a more forgiving RF environment, both receivers will be equally adept and digging out weak weak and challenging DX signals. I plan to investigate this very scenario in a few weeks at a quiet location on the Oregon coast.

Side note: I have two HF+ units and they can operate concurrently without problems for full medium wave band coverage with HSDSR software, even when both are recording IQ WAV files.

Guy Atkins is a Sr. Graphic Designer for T-Mobile and lives near Seattle, Washington.  He’s a regular contributor to the SWLing Post.

AM Radio: Ivan compiles 2017 solar eclipse logs

Many thanks to SWLing Post contributor, Ivan Cholakov (NO2CW), who writes:

I never got a chance to summarize my results of the AM scans I did during the 2017 total eclipse.

I used an SDR and a 40 foot end-fed antenna located in a park near the Nashville, TN airport.

On the plus side I did notice a spike of AM signals and amateur radio signals especially on 40 meters. On the negative side, my AM scans were adversely affected by the nearby powerhouse WSM transmitter on 650 kHz.

I’ve attached my results in a spreadsheet [embedded] below.

Click here to view this Google Docs spreadsheet in a new window.

Fantastic, Ivan! Thank you for taking the time to go through your recordings and make these notes. No doubt, this log took a few hours to compile. I’ve yet to go through my eclipse spectrum recordings–!

Again, thanks for sharing!

Click here to view Ivan’s previous post which includes a bandscan of the 2017 Eclipse QSO Party.

Radio Deals: A few last-minute gift ideas!

Many thanks to SWLing Post friend “Karen” who writes:

My husband reads your website every day and is a dedicated radio geek. I’ve decided I’d like to get him an extra last minute stocking stuffer for Christmas.  Any suggestions? We buy a lot from Amazon and are Prime members but any retailer that could get something delivered by Friday would work fine. Since this is a stocking stuffer, I don’t really want to pay more than about $70-90.

Thanks for your inquiry! Readers, “Karen” has kindly allowed me to post her message publicly and no that’s not her real name–!

Karen, you didn’t mention what radios he currently has, so you may double check before committing. I’ve listed a few options with links below. This list is by no means comprehensive–I just did a quick scan of a few retailers based on what’s currently a good deal and can be shipped ASAP.

Since you like Amazon and  get free two day shipping via Prime, I’ll list several options there. I’d also encourage you to check with radio retailers like Universal Radio, Ham Radio Outlet and C. Crane–they, too, can ship via two or one day service, but it might be at a premium.

Just note to check the delivery date very carefully as we are down to the wire! Note that prices, especially those at Amazon, can change without notice.

Last minute stocking stuffers for the radio enthusiast

Thank you for your question, Karen, and for allowing me to post your message, thus my suggestions, publicly. Since you asked specifically about Amazon, and since you get free two day shipping, I focused on Amazon offerings here. Note that my links are affiliate links and if you chose to purchase using one of these links, the SWLing Post will receive a small commission at no cost to you.

With that said, please consider purchasing from one of the radio retailers I mention above. The total price may exceed Amazon’s, but you can actually call these retailers to place orders and ask questions.

Post Readers who live outside of the US will have to check with radio retailers in their country regarding pricing and shipping on the items above. I wish I had time to list links to international options. Perhaps readers can comment with links and other suggestions?

Good luck and Happy Holidays!