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Old 3rd Mar 2021, 9:58 am   #1
Davidsteam
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Default Howes audio filters

I am unable to resist 'interesting' looking items at bootsales, radio amateur sales etc. I bought a diecast box with a couple of 1/4" jack sockets and to multi position rotary switches. Now ive got around to playing with it im a little confused. It contains a larger than necessary mains transformer, Howes ASL5 and a Howes CSL4 audio filter PCBs.

I wonder why it has both, looking at adverts in old magazines they appear do the same job except the ASL5 can drive a loudspeaker. The boards appear to be similar except the ASL5 has an LM380 so it can drive a loudspeaker.
I think the ALS5 is intended as a self contained unit and the CSL4 to be built into a receiver?

The 2 rotary switches have only 3 active positions, presumably OFF, CW and SSB, but different wafers of the same switch serve the 2 boards.

Im curious what is going on, is it to achieve a very sharp notch for cw, or are the component values changes to modify the responses?

Ive searched for a connection sheet but no luck, does anyone here have any information to help?

Many thanks
David
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Old 3rd Mar 2021, 10:38 am   #2
dodgy-dxer
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Default Re: Howes audio filters

David

See

http://www.gqrp.com/howes.htm

Fred
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Old 3rd Mar 2021, 10:40 am   #3
mickm3for
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Default Re: Howes audio filters

Hi contact the gqrp group http://www.gqrp.com/howes.htm they have info on Howes kits Mick
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Old 3rd Mar 2021, 11:42 am   #4
Davidsteam
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Default Re: Howes audio filters

That's great thanks.
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Old 3rd Mar 2021, 8:11 pm   #5
John KC0G
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Default Re: Howes audio filters

David, you are correct about the ALS5 being designed to be an external unit, and the CLS4 being an internal unit. Please see:
https://web.archive.org/web/20020625...-html/asl5.htm
https://web.archive.org/web/20020623...-html/csl4.htm
It makes me wonder if the person who put these together put the two in series for extra roll-off?

Hopefully the GQRP will be able to supply the data. Otherwise it should not be too difficult to work out the connections.

73 John
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Old 3rd Mar 2021, 10:55 pm   #6
m0cemdave
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Default Re: Howes audio filters

The construction notes for the ASL5 actually suggest that a CSL4 can be added for "even greater selectivity" and I have seen a few examples built like that.
However it's pointless really because either filter works very well on its own. The CW filter is very sharp and surprisingly good at pulling a signal out of noise and nearby QRM.

I have several of these boards either as standalone amplifiers (ASL5) or built into homebrew receivers (CSL4).

It's quite easy to change the CW filter values - all mine have been set to 750Hz and are about 200Hz wide.

You may find it useful to remove the CSL4 and use it independently, if you have an existing receiver that would benefit from the addition of a tight CW audio filter.
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Old 7th Mar 2021, 12:08 pm   #7
Davidsteam
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Default Re: Howes audio filters

I've not yet seen any Data sheets for these items, but as suggested, can work out the individual switch connections, I guess the 'C' and 'S' being the CW and SSB connections.

I'm guessing, if I feed white noise into a filter, and put an audio spectrum analyser on the output, I will get the typical graphical response curve?

Much easier to use a couple of smartphones instead of manually plotting spot frequencies and measuring levels with a dB meter and drawing a graph. I remember doing this in the telecommunications world almost 40 years ago to check audio responses in equipment.

David
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