Tag Archives: Review

Digging in the Noise: Weak Signal Audio Recovery with the AirSpy HF+ and Elad FDM-S2

I’m currently spending the better part of a week at Cape Lookout State Park on the Oregon coast, with a great view of the ocean through tall evergreen trees. This is one of my favorite parks in the Pacific Northwest, especially when DXing during the blustery winters from one of the nice cabins at Cape Lookout.

The view from the beach near my cabin; the turbulent waves were a precursor to the gale force winds at the park during the night of the 23rd!

Although I’m at the park for trans-Pacific medium wave DXing, I’m also comparing receivers, both SDRs and portables. This morning I sought out a few weak shortwave signals, pitting the Elad FDM-S2 SDR ($529 USD) against the AirSpy HF+ ($199 USD). I have a pair of the HF+ receivers to cover all of medium wave (as the FDM-S2 easily does). Many SWLing Post readers already know that the upstart HF+ trades bandwidth to gain high performance in order to keep the price reasonable.

My antenna used for the following recordings was a small “Flag” antenna using a Wellbrook Communications FLG100LN module and a 2K ohm variable potentiometer for termination. The design uses crossed tent poles in an “X” formation to support the wire loop. This design travels easily in a compact package; I have Dave Aichelman of Grants Pass, Oregon to thank for this very useful “tent pole loop” implementation of the Wellbrook FLG100LN.

The Wellbrook-based antenna functions superbly, and its low-noise design helps hold down QRM from the nearby cabins (which unfortunately have been “upgraded” recently with noisy cold fluorescent [CFL] light bulbs). The area around the Cape Lookout cabins used to be superbly low noise and suitable for radio listening, but now it is more of a challenge than before. The Wellbrook FLG100LN is perfect for the situation though; Wellbrook ALA1530LN  Pro and ALA1530S+ 1-meter loop antennas work commendably at the park too.

The Wellbrook FLG100LN module with a home brew RFI choke in-line

A 2K ohm variable potentiometer is protected from the elements in a small plastic bag. The “pot” is adjusted for the best nulling of medium wave stations off the back side of the antenna’s reception pattern.

The “tent pole loop” antenna is strapped to a fence railing with ultra-strong Gorilla Tape to keep the 7-ft. square loop vertical.

On with the recordings…

For the FDM-S2 and HF+ comparisons I used the SDR-Console V3 software. Every parameter was identical for the receivers–sampling bandwidth, filter bandwidth, AGC, mode and so on.

Take a critical listen to the weak signals recorded with the SDR receivers, identified as only “Radio A” and “Radio B”. A link to a poll is at the end of this article; please indicate which recording of each pair has the most intelligible audio in your opinion, and submit your choices when you’ve made up your mind on each audio clip. After a week or so I’ll post the results of the voting, and identify the receivers.

9.615 MHz, LSB, Radio A


9.615 MHz, LSB, 
Radio B (note: the same male announcer heard in clip “A” begins at 00:14 in this “B” clip)

 

9.730 MHz, USB, Radio A


9.730 MHz, USB, 
Radio B

 

7.230 MHz, S-AM, Radio A


7.230 MHz, S-AM, 
Radio B

 

9.860 MHz, S-AM, Radio A


9.860 MHz, S-AM, 
Radio  B

 

Note on 7.230 MHz recording: this was an interesting frequency, as the signal was tightly surrounded by a very strong local 40m ham radio LSB station as well as a strong China Radio International signal. There were other strong amateur and broadcast stations within 30-50 kHz of 7.230 MHz, also. This A-B test more than the others may indicate receiver performance in a strong RF environment on a crowded band.

Ready for the poll? Register your votes at the Google Docs form below:

https://tinyurl.com/ya38wj69

In a week to 10 days I’ll post the results in another article. NOTE: I haven’t provided a “both sound the same” choice in the poll to encourage you to ‘dig deep’ into the audio and listen critically–to find something that stands out in one clip versus the other.

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

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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.

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On sale now: the CommRadio CR-1, a great little receiver

IMG_8048

[UPDATE: Check out our full review of the CR-1 by clicking here.]

A hot tip:  currently, CommRadio offers the CR-1 software-defined tabletop receiver for just $500 (US), until August 1, 2013. Check out the sale on CommRadio’s website and at Universal Radio.

I have been using the CommRadio CR-1 for almost two months now. I had planned to provide a brief review for The SWLing Post by early July, but my travel schedule has simply been too hectic.

MTcover0813coverlgFortunately, however, I offer a full in-depth review in the August 2013 issue of Monitoring Times magazine (incidentally, their turn-around time from submission to print is simply amazing). If you subscribe to MT–or can get your hands on a copy–you will have my full review.

Many of you have been asking me for my thoughts on the CR-1 so you will know whether or not to take advantage of promotional pricing.

In a nutshell, here is the answer your question:

Q: Is the CommRadio CR-1 a good deal?

A: Yes!

Though I was skeptical about this little receiver when I first saw the announcement in January, the CR-1 truly does hold its own. It’s a sturdy radio built with longevity and performance in mind. It’s the little touches I love: a near-perfect tuning knob (in my opinion), size & portability, multiple antenna jacks, an excellent internal battery and gold-plated circuit board pads…Performance-wise, the CR-1 has great sensitivity and selectivity on the HF bands…

Though there are a few negatives, in my book, the positives far outweigh them. If you really want to dig into the juicy details, I would encourage you to check out my full review in the August 2013 issue of Monitoring Times magazine (especially since MT, sadly, is slated to stop publishing at the end of the year).

If you’ve been on the fence about buying the CR-1, I would encourage you to give it consideration before August 1st, 2013, when the price increases to $599 US.

Here is the press release from CommRadio regarding the current $500 sale:

(Source: CommRadio)

CR-1 News for Friday, July 26th, 2013

Our Promotional Price of $500 will increase on August 1st.

All orders made after July 31st will be priced at $599 (battery included).

Order now before the price goes up.
www.commradio.com

Please note we are working hard to get all radios out as soon as possible, although the lead time could be up to 4 – 5 weeks starting this week (7/24/2013)

For any questions about ordering and shipping

or international orders please contact

Lizz Arias

lizz.arias@aerostream.com

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