Month: September 2018

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.

SSB NFD with G3PYE

The Camb-Hams operated from a new site this year, due to their usual site being unavailable. The location had good unobstructed views, the local area is very flat but it did have such a good elevated VHF take off.

The event falls at the end of the year and providing a chance to catch and discuss the year’s events.

This year the team had 3 van based masts, their own Transit based Flossie with its 22m mast, as well as the recently purchased Mercedes Sprinter ex OFCOM van owned by Colin that comes with a 25m mast.

Geoff G0DDX also had his 12m vehicle mounted SCAM mast.

VHF was operated from Flossie, while HF was from Colin van with the 3e Triband beam at 25m.

 

The SSB FD rules have recently changed, the maximum power is limited to 100w. This can make it hard going as I would guess some of the EU stations are running a little more power. The contest also runs alongside the worked all Asia contest, adding another dimension to the band.

We also enjoyed a BBQ by torchlight, a field day favourite.

The drone provided some aerial video and pictures from the event.

 


Thanks for an enjoyable weekend.

© 2015 Dave, M0TAZ