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Wideband Loop Signal Chains with Software Defined Radio

wideband loop signal chains

You need to understand your wideband loop signal chains and their limitations. Then, you can get the most performance out of your radio investment.

Last year, I did some articles on the challenges of using wideband loops with modern software defined radios on HF and below. Wideband active loops are a wonderful combination with wideband SDR receivers. They amplify signals over a broad spectrum and let you listen easily to combinations of low, medium and high frequencies with just one antenna.

But if you live relatively close to local AM broadcast transmitters, these really strong signals can easily overload the analog-to-digital converter (ADC) in your radio. You need to consider complete wideband loop signal chains at your location. You have three tools to handle contingencies: attenuation, bandpass filtering or more bits in the ADC.

Above, you can see the wideband loops signal chains in all five of my SDR for HF reception (3-30 MHz). Shown in dotted lines are the bandpass filters you can use to knock down strong out of band AM broadcasters. My Flex 6300 has no bandpass filtering, but the ADC has enough headroom to prevent overload. On the other hand, my Afedri dual channel receiver requires an outboard high pass or MW band reject filter to remain useful on HF with strong local broadcasters nearby. My low cost Distill AM Broadcast Reject filter does the job nicely.

Interestingly, my ANAN-7000DLE MKII is essentially a two-channel Perseus, with just the right amounts of attenuation, bandpass filtering and gain to get the job done.

The medium wave band reject filter on the RSPduo also does a great job of preventing AM broadcast interference in the shortwave bands. With the exception of the Afedri, these wideband loop signal chains are great on HF.

Wideband Loop Signal Chains on Medium Waves

Shown below are these same wideband loop signal chains when used for medium wave reception.

wideband loop signal chains

Typically, all you need is some front end attenuation of say 10-20 dB to get things under control. Both the Afedri and Flex use digital gain control to reduce overload before the ADC. The Perseus and ANAN provide switchable attenuation. Unfortunately, while the RSPduo provides gain reduction, by the time to reduce the AM signals enough AM reception signal-to-noise ratio is poor in my location. So, I switch in some external attenuation when I want to do medium wave DX on the SDRplay.

Also last year, I did some articles on a DIY wideband loop helper to provide either dual channel attenuation or filtering.

Each of my five SDR has a lot to offer when used with a loop antenna, as long as I keep the limitations of the wideband loop signal chains in mind.

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