BCFM filter (was: Re: [airspy] Best Gain Settings for 137 mhz reception}


David J Taylor
 

Hello friends:

Thank's again for ALL your posts.
I'm learning a lot with this thread.
Today i have received the BCFM Notch filter and it is doing a GREAT Job.
Finally i bought RTL-SDR BCFM Filter.

One more question:
Where is the best place to install this filter?
My setup now is:
Antenna --> BCFM Filter --> LNA4ALL --> Coax --> Airspy R2

This evening i will test with NOAA's and Meteor M2.

Thank's again.
===========================================

Someone asked about the response of that filter so, at great expense (!), I bought and measured one:

http://www.satsignal.eu/Radio/ddamtek-filters.html#RTL-SDR

It works as advertised, but I am not convinced about my own measurements of ripple in the passband.

73,
David GM8ARV
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk
Twitter: @gm8arv


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Ruben Navarro Huedo (EA5BZ)
 

Thank's for the test David.

What means " ripple in the passband " ?


David J Taylor
 

From: Ruben Navarro Huedo (EA5BZ)

Thank's for the test David.

What means " ripple in the passband " ?
=============================================

Ruben,

I mean that there appear to be small variation in the passband - usually less than 1 dB - which might be likened to ripples on water. I am not convinced that my test is correct.

73,
David GM8ARV
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk
Twitter: @gm8arv


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Ruben Navarro Huedo (EA5BZ)
 

I understand :)

Thank's a lot


Ruben Navarro Huedo (EA5BZ)
 

David:
Speaking about DD amtek bpf-air 
Do you know if I can pass dc through it?

Tnx


W0LEV
 

I can't speak for that specific filter, but typical BPFs have shunt parallel resonators coupled by either capacitors and/or inductors between the parallel resonators.  As such, they would exhibit a short circuit to 'ground' from either port.  If the ports are coupled with capacitors or tapped capacitors, no DC would pass.  So, for a typical BPF, you get either no DC or a short circuit.  However, not to say someone out there uses a 'large' RF choke to bypass the whole filter so it would pass DC.  This is very atypical.

Dave - WØ LEV  

On Wed, Sep 20, 2017 at 12:39 PM, Ruben Navarro Huedo (EA5BZ) <runahue@...> wrote:
David:
Speaking about DD amtek bpf-air 
Do you know if I can pass dc through it?

Tnx




--
Dave - WØLEV
Just Let Darwin Work


David J Taylor
 

From: Ruben Navarro Huedo (EA5BZ)

David:

Speaking about DD amtek bpf-air Do you know if I can pass dc through it?

Tnx =========================

Ruben,

The socket side is DC short-circuit from centre pin to ground

The plug side has no DC connection.

I'm slightly surprised it's not symmetrical. Thanks for Dave's input, too.

73,
David GM8ARV
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor@blueyonder.co.uk
Twitter: @gm8arv

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prog
 

On Wed, Sep 20, 2017 at 04:18 pm, David Eckhardt wrote:
However, not to say someone out there uses a 'large' RF choke to bypass the whole filter so it would pass DC.  This is very atypical.
Just an illustration.


SkipF, NT1G
 

Do you mean BANDPASS/D.C. pass?
That's TWO bands...


adam9a4qv
 

A very bad example.


prog
 

Illuminate us with a better example.


Ruben Navarro Huedo (EA5BZ)
 

TNX a lot for all replies.
Again: I am learning a lot in this group.


adam9a4qv
 

Doing this on 2.2 MHz is different than using the same approach on 137MHz, in practice.


prog
 

It all depends on the quality of the choke (Parasitic parallel capacitance, SRF, etc.) Coilcraft produce some good (expensive) conical inductors for this kind of setups, yet it's an extreme case to be avoided when possible.