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2.5 MHz low pass fiilter uses no toroids, SMDs #ubitx


Peter Parker
 

I've been experimenting with various types of low pass filters to cure BCI. 

My starting point was the VK3IL design. Then I changed the values to use prewound 2.2 uH RF chokes I had.  Increasing the capacitors by a similar factor (approx 1.5 times) dropped the cut-off frequency to around 2.5 MHz.  This may offer somewhat less attenuation of the broadcast band but does mean that the uBitx will tune WWV on 2.5 MHz without too much loss.  Also 160m reception should be possible on stronger signals.  The big benefit (for some) is there's no need to wind your own toroids.  And you can use conventional components on a small circuit board that can be sawn to make the pads.  

I'm pleased with its performance. More in this video. 

https://www.youtube.com/watch?v=fgQenFJOjr4

73, Peter VK3YE

 


Howard Fidel
 

You made a high pass filter, not low pass.

On 6/10/2018 9:12 PM, Peter Parker wrote:

I've been experimenting with various types of low pass filters to cure BCI. 

My starting point was the VK3IL design. Then I changed the values to use prewound 2.2 uH RF chokes I had.  Increasing the capacitors by a similar factor (approx 1.5 times) dropped the cut-off frequency to around 2.5 MHz.  This may offer somewhat less attenuation of the broadcast band but does mean that the uBitx will tune WWV on 2.5 MHz without too much loss.  Also 160m reception should be possible on stronger signals.  The big benefit (for some) is there's no need to wind your own toroids.  And you can use conventional components on a small circuit board that can be sawn to make the pads.  

I'm pleased with its performance. More in this video. 

https://www.youtube.com/watch?v=fgQenFJOjr4

73, Peter VK3YE

 



Peter Parker
 

You're quite right!  Oops! 


John Sharpe
 

Dammit Peter!

Why couldn’t you have posted that a week ago!
I‘ve just finished building a Minikits 1.8Mhz high pass filter. http://www.minikits.com.au/HPF11-1M8 

It's a great filter but has six toroids and cost more than yours would!

The Minikits filter has made a dramatic difference to receive on my Bitx40.

Cheers, John

VK2VOL

On 11 Jun 2018, at 11:12 am, Peter Parker <vk3ye@...> wrote:

I've been experimenting with various types of low pass filters to cure BCI. 

My starting point was the VK3IL design. Then I changed the values to use prewound 2.2 uH RF chokes I had.  Increasing the capacitors by a similar factor (approx 1.5 times) dropped the cut-off frequency to around 2.5 MHz.  This may offer somewhat less attenuation of the broadcast band but does mean that the uBitx will tune WWV on 2.5 MHz without too much loss.  Also 160m reception should be possible on stronger signals.  The big benefit (for some) is there's no need to wind your own toroids.  And you can use conventional components on a small circuit board that can be sawn to make the pads.  

I'm pleased with its performance. More in this video. 

https://www.youtube.com/watch?v=fgQenFJOjr4

73, Peter VK3YE

 


Glenn
 

Thanks Peter,
I made one up using SMD parts on a bit of proto board.  Picture of the board and response attached. Yet to fit it, but looks great.

glenn
vk3pe



On Sun, Jun 10, 2018 at 06:12 pm, Peter Parker wrote:

I've been experimenting with various types of low pass filters to cure BCI. 

My starting point was the VK3IL design. Then I changed the values to use prewound 2.2 uH RF chokes I had.  Increasing the capacitors by a similar factor (approx 1.5 times) dropped the cut-off frequency to around 2.5 MHz.  This may offer somewhat less attenuation of the broadcast band but does mean that the uBitx will tune WWV on 2.5 MHz without too much loss.  Also 160m reception should be possible on stronger signals.  The big benefit (for some) is there's no need to wind your own toroids.  And you can use conventional components on a small circuit board that can be sawn to make the pads.  

I'm pleased with its performance. More in this video. 

https://www.youtube.com/watch?v=fgQenFJOjr4

73, Peter VK3YE

 


Peter Parker
 

Thanks Glenn!  I do wonder whether 680pF would have been better than the 820pF I used - might shift it up a little which might be desirable for those near a powerful station around 1.5 MHz (in VK most of the really powerful AM stations are ABC below about 900 kHz). 


Glenn
 


Hi Peter
Yes I guess that might be a bit better although I haven't listened much on my rig so far to know how bad the BC is here. I am in Narre Warren Sth. I think the nearest BC station Tx is at Mulgrave, not even sure which one it is frequency wise.
I will see if i can do a plot though, asap.

glenn


On Mon, Jun 11, 2018 at 01:07 am, Peter Parker wrote:
Thanks Glenn!  I do wonder whether 680pF would have been better than the 820pF I used - might shift it up a little which might be desirable for those near a powerful station around 1.5 MHz (in VK most of the really powerful AM stations are ABC below about 900 kHz). 


Peter Parker
 

Mulgrave is 3MP on 1377 kHz. So it would be a good test of the filter. 

Was listening with it tonight and all was good.  Could hear interstate stations on 1548 but not local stations below about 900 kHz.  160m amateur reception would probably be down but OK. 

If you wanted better rejection you could just use VK3IL's capacitor values plus RF chokes for 1.5 uH.   


Peter Parker
 

A further update. Couldn't resist joining the early morning 160m SSB net on 1860 kHz.  I can confirm that my values give satisfactory sensitivity on 160m.  Loaded the G5RV against the kitchen plumbing. 

Heard by VKs 3CAF, 3AX, 5IS.

Some distortion / RF feedback due to the non-use of balanced antenna, shielded coax and plastic case for tx. 

You would need to add an LPF for routine operation on 160m. 


VK3HN
 

Good looking trace from a HPF made of surface mount inductors and capacitors. I'm not surprised by the use of s.m. caps but inductors does surprise a little.  I would have hand wound them on T37-2 (at a minimum).  Are they anything special Glelnn?  --Paul VK3HN.  

PS: I want a Rigol DSA815 (!)


Glenn
 

Hi Paul,
I wanted something fairly small and quick hence no toroid winding, and looking  through my SMD inductor box, found the ones shown. 1812 footprint. Nothing special. Similar parts available from Element14 at about 50c. 2493202

The Rigol SA with tracking generator is a VERY handy thing to have for homebrewers. There is also the newer but similar Siglent  SSA3000x series,  that's slightly more expensive. (I have no ties to either of these companies)

Glenn
vk3pe


On Mon, Jun 11, 2018 at 08:47 pm, VK3HN wrote:
Good looking trace from a HPF made of surface mount inductors and capacitors. I'm not surprised by the use of s.m. caps but inductors does surprise a little.  I would have hand wound them on T37-2 (at a minimum).  Are they anything special Glelnn?  --Paul VK3HN.  

PS: I want a Rigol DSA815 (!)