Tag: sdr

Hermes Lite v2 a 5w SDR

The Hermes-Lite is a low-cost direct down/up conversion software defined amateur radio HF transceiver based on a broadband modem chip and the Hermes SDR project. It is entirely open source and open hardware, including the tools used for design and fabrication files.

Hermes Lite V2 SDR

The SDR is controlled over your LAN, and plugs into your router. This can provide both local and remote operation. You can read more online about the project on the Hermes website.

The board comes fully installed, although you do need to follow the instructions on thermal dissipation for the PA. The radio will deliver 5w and is suitable for all modes and works particularly well on digital modes.

The microphone can be plugged into your PC, and then defined as the soundcard on the radio. In this audio clip, you can hear Gerald G4AXP (40w), and M0TAZ (5w) both using Hermes Lite SDR to have a chat on 5 MHz. In this case, I was using a cheap USB headset as I find headphones often help with noisy HF bands.

M0TAZ 5w and G4AXP 40w both using Hermes Lite SDR radios

The example RX filter setup in Spark SDR shown here.

The radio needs to be controlled by software locally installed on your PC, and you have a wide choice. I started with SparkSDR, as this program has a number of really neat features. The ability to have 4+ receivers running decoding digital modes on the fly. You will find SparkSDR have a online forum for questions and support.

Decoding 4 bands FT8 simultaneously

Here we will look at the setting to use Spark SDR with WSJT-X, setting up the sound card option, and radio mode set to DIGIU and hamlib.

You can use VAC to feed another digital program
Audio Settings
Enable Rigctl CAT
General setting page

In WSJT-x you need to set the rig to Hamlib NET rigctl and Network Server to your local IP address of the PC using port 51111

Network Server to PC IP address port 51111

Here we see WSJTx configured with SparkSDR and Hermes receiver decoding FT8

Its possible to do FT8 and other digital modes directly in SparkSDR, you dont even need to VAC but its good to have control as we can use this with other programs.

SparkSDR can be integrated with FLdigi using Hamlib

I have been running the Hermes Lite now for a few days. 140 QSO most FT8 or FT4 between 3 to 5w. This reception report is amazing, not worked but nice to know you have potential. ZL4AS

Broadcast Overload on Kiwi SDR

The Kiwi SDR and Wellbrook loop provide a very good single antenna solution for 0 to 30 MHz shortwave reception. The Kiwi is capable of displaying the complete band of 30 MHz, but the disadvantage is the very high power from some of the LW and MW stations can cause the receiver to overload in the evenings.

One approach would be to build a notch filter to attenuate just the one or two strongest signals, in my case this would have been 909 kHz Radio Five Live from Brookmans Park, and 1332 kHz Christian Radio. The problem I had was in the evening this would often change, and at times some of the continental AM stations would become an issue.

The alternative would be a bandstop filter, that would just attenuate the MW band. We also have two amateur allocations at 472 kHz and 1.9 MHz that I would like to receive, with the medium wave band in the middle. The solution would seem to be a bandstop produced by Nooelec. The units retail for around 11 dollars in the USA, you can get them from Amazon or eBay for around 16 GBP with free delivery.

They say on their website “We designed Distill:AM to provide sufficient attenuation for broadcast AM frequencies (>40dB typical) while ensuring adjacent bands, such as 160m, are minimally affected. The -3dB rolloff of the filter is 350kHz and 1900kHz. Minimal out-of-band insertion loss means the filter can stay in place for most any application, though we do recommend removing Distill:AM from your setup when not listening to HF frequencies. As a true bandstop filter, you are able to pass-through DC (bias power) when it is required.”

You can view the data sheet below.

I found 909 kHz reduced from around -20dBm to -50dBm so this helped reduce any signal overload.

You can read more or use the Kiwi receiver here.

The Welbrook look is an active broadband receiving loop antenna.

Nooelec have a range of products online.

Comparing the Wellbrook Loop to a Doublet Antenna

This evening I decided to complete a test using two different HF setups in an effort to compare the receiver performance of my antennas.

Radio 1, Kenwood TS 990, doublet antenna 10m per leg @ 9m

Billy offers support.

Billy offers support.

Radio 2, Elad SDR, Wellbrook RX loop @ 3m

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I decide the best way to test on receive would be to leave both radios receiving on 7076 KHz for 90 minutes, using WSJT-X. Both receivers had been set to 3 KHz bandwidth, and over the course of the next 90 minutes they each collected over 600 measurement reports.

The test started at 1830 Hrs and continued to 2000 Hrs. The doublet collected 633 measurement reports, and the wellbrook 740. This was the first indication that the Elad coupled with the Wellbrook was out performing the Kenwood / doublet setup. The next stage was to look in detail at the reports, WSJT has an option to write all received data into a text file, this includes time, s/n and decoded text. I used this to select at random some calls that represented a selection of EU (and DX if possible) and compare the relative signals received at the very same time on both radio 1 and 2.

The following table shows a selection of data points

wellbrook v doublet

After reviewing the data it was clear the Wellbrook loop improved the quantity of stations decoded, and in many cases also improved the s/n received.

This is by no means a definitive test, but it does indicate the Wellbrook loop (as many others have reported) work well in somewhat noisy urban environments.  The wellbrook loop can be reviewed online at the Wellbrook communications website, the version I used for the tests was ALA1530  its 1m and designed for medium and shortwave 50 KHz to 30 MHz. Steve Nichols G0KYA completed a review in January 2012 Radcom You can see the Eznec plot as photo 3 in the review.

The other factor to consider is the loop antenna has some directivity, I didn’t rotate the antenna at any point during my tests. In many cases rotation will improve / reduce signals as the antenna has directional properties.

The Welbrook performed well on 7 MHz, I suspect it would be even better on 1.9 and 3.5 MHz… to be continued….

Dave M0TAZ