A good old active filter...

Nowdays everything is digital. I hear old mates talking on 40 meters complaining of the voice of their brand new HF radios. Digital … as they say... never sounds as good as those old rigs with tubes inside.

I have been using an FT-450AT for a while. Why FT-450? When I moved to Hungary it was the cheapest piece from a trusted seller. It has everything I need, specially narrow CW filters. Almost a decade ago I had an IC-7200 I really loved. FT-450 is very similar in it's category. Of course just similar, but not as good. Okay, I am not complaining, it does it's job, and for a casual ham like me it is more than enough. It is not a contest “king of the field rig”, but if one is able to understand it's features this radio can be a good friend.

This post is not about FT-450, there is something else. 

Few weeks ago I had a deal with a local ham. Finally I received an old DAIWA AF606K filter. Originally I wanted an external speaker, but I was curious, and it has a big speaker inside, so why not to give it a try?

It is built like a tank. Reminds me pretty much the good old 80's. Basically it is an active filter for SSB and CW mode. There is a PLL function is, but I would not use that in real life.

It has four knobs on the front. Notch, PLL lock frequency, band pass for CW and mode. Input is low impedance, so speaker can be connected straight. When turned off, it behaves like a speaker, turning it on the filter starts working.

I have almost broken it at the first time. Pwr supply connector is reversed... inside is negative and outside is positive. Ghrrr... I changed it so quickly therefore it fits to my domestic standard. After trying it I noticed a strong feedback noise in SSB. I checked the whole station, and found everything fine. The weakest chain was the filter. Also the speaker had terrible voice, while using my headphone it was perfect.

After several minutes I found the problem. Few ferrite filters inside, and proper ground connection between the front panel and the PCB made it OK.

Result is amazing. I really like listening CW QSO parties, and also taking part... The filter saved me dozens of pain killers. I turn on narrow CW filter on the 450, and turn on the filter, play with the notch, and no noise, no static, just the pure signal. No matters how weak the signal is, it makes it easy to copy, easy do dig out from the noise and above all CW reception has become relaxing.

If you find one on a hamfest, or even ebay, do not hesitate to buy!

I will make a short video clip later to show what it does... and picture as well of course.