Filters for FT-817 from SOTABeams

Just seen on Southgate news - plug-in SSB & CW digital filter board for FT-817 from SOTABeams for under €60.



I bought the wide/narrow SSB version at Norbreck and have been playing with it over the last few weeks - shape factor is amazing, measurements show it does “what it says on the tin” and particularly on the narrow setting reduces perceived noise.

Not had a chance to try it on an activation yet, but am thinking it may significantly help with dealing with the all-too-prevalent QRM and splatter from the QRO stations that always seem to open up about 1kc/s off my frequency around 10 minutes into the activation :-s

Right, I’m off to take my modulation transformer to the weighbridge. Ooops wrong thread :confused:

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It’s amazing how often that happens Paul. It’s almost as if these QRO stations, who know nothing about SOTA or QRP are drawn like a magnet to 1 KHz away from an activator - really weird how often it happens!

Back to the filters - well as more and more crystal filter manufacturers are stopping creating filters, it’s good to see that there are “after market” companies willing to design and build plug-compatible digtal filter boards.

Well done Richard on carrying these units!


Correction - as per Richard’s comment, the filter board is not a plug-in replacement and if to be installed internally some installation skills are required. The Southgate News article states that SOTABEAMS offers a fitting service in the UK through “M0HET Electronics”.

Hi Ed

Just a small correction; these are not plug-in filters.

73 Richard G3CWI

…And just to clarify mine is an external unit that I’ve built into a small case together with an audio amplifier to drive headphones/speaker so I can use it with a variety of radios.

Also intend trying it for Tx audio processing when I get a chance. Clipping and tight filtering should improve talk power considerably :slight_smile:

73 de Paul G4MD

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Remember these are audio filters.

They will not help with close in QRO QRM that overloads the front end of your radio and de-senses it. For that you need a filter in the IF chain like the plug in ones designed for the rig.

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Exactly. The concept is very similar to the Datong FL-1 audio filter, designed by Dr David Tong in the 1970s. However the FL-1 was an outboard unit which was connected in series with the audio output line from the receiver … and it was an analogue filter dating from the days well before “digital” things became the norm.

Walt (G3NYY)

I’m well aware of the limitations of what I’m trying to do but figure that getting rid of the predominantly high frequency elements of the crunching that comes through will help intelligibility and make listening a little less painful.

That it certainly will - the 857 can be set for various high and low AF cut-offs and playing with these shows that you can alleviate some of the QRM. No doubt a narrower filter in the IF chain would be even better but every little helps!


[quote=“DD5LP, post:3, topic:13308”]drawn like a magnet to 1 KHz away from an activator[/quote]Slightly less troublesome than the VDSL re-training combs that always seem to have one sprog or another land about 10Hz from an activator…

These filters are several leagues ahead of anything possible with analogue circuitry.

The skirts are so steep, tuning a signal generator through the cutoff frequencies, it’s as if the generator has been switched off :slight_smile:

Looking forward to trying them with simple DC receivers too.

73 de Paul G4MD