[minima] Re: Linear Output Filter Switching

  • From: Mark G0MGX <mark.g0mgx@xxxxxxxxx>
  • To: minima@xxxxxxxxxxxxx
  • Date: Sat, 01 Feb 2014 17:28:58 +0000

Isn't this:


exactly what we need to go from Binary outputs on our 3 digital lines to individual relays controlling filters?


On 01/02/2014 15:26, farhanbox@xxxxxxxxx wrote:
There's something not right about the curve. The stopband is quite nominal. You 
must get atleast 60 db stop-band.

Sent from BlackBerry® on Airtel

-----Original Message-----
From: Mark G0MGX <mark.g0mgx@xxxxxxxxx>
Sender: minima-bounce@xxxxxxxxxxxxx
Date: Sat, 01 Feb 2014 13:47:38
To: minima@xxxxxxxxxxxxx<minima@xxxxxxxxxxxxx>
Reply-To: minima@xxxxxxxxxxxxx
Subject: [minima] Re: Linear Output Filter Switching

Hi Team

I've started the output filter Wiki page here:


and have so far put info on 4, 11 and 19MHz cut off Low Pass Filters. I
am very unhappy with the 19M filter sweep, so will let you guys take a
look before doing any more. The next filter needs to be 30M cut off - we
already have one of those!

As an aside I have dug out my CD from EMRFD and mine is a 2002 version
of the software which I can't find a filter designer? I can enter values
myself but cant get the software to come up with the filter for me -
hence I have stuck with what I know and used QUCS for my designs.

I do think that we could still use the existing D5 line for output _*as
well as*_ the existing input filter switching just so long as the line
stays HIGH for > 15MHz and LOW for <= 15MHz. This would give us room for
a 1.8M filter and another if we find we need i. I  have only focused on
those highlighted yellow below, but clearly with the three digital lines
we could have up to 8 filters if we needed them.

I personally like the idea of simple logic chip or BCD type logic to
control relays as I feel that we want to avoid more programming and
complexity where it's not needed. The 74LS139 idea is a great one and
probably the way I plan to go, but lets see what we decide.

I've tried to explain some of this in the Wiki - please take a look and
lets decide between us how we are going to do this part of the project.

We could of course go with the idea of a separate amplifier completely,
maybe with the tubes others are suggesting! I've never built anything
with tubes....


On 01/02/2014 06:48, Mark wrote:
Thanks to everyone for the suggestions and ideas.

If we go with 4 filters have we scrapped top band?

I'll try and run some designs for the four suggested filters and build
some prototypes and stick the results on the wiki.

We can then decide and discuss what we think we should do.

From: Ashhar Farhan <mailto:farhanbox@xxxxxxxxx>
Sent: ‎01/‎02/‎2014 05:00
To: minima@xxxxxxxxxxxxx <mailto:minima@xxxxxxxxxxxxx>
Subject: [minima] Re: Linear Output Filter Switching


I have been mulling over this ... and I am trying to balance quite a
few things here.

1. Can we make do with just four filters? I have attached a screenshot
of a simulation I ran (both these programs are available on the EMRFD
CD). As you  can see, a filter can be cut for 7 and 10 mhz. The 7
mhz's second harmonic at 14 is down by 25db. Which means, if we don't
distort the linear too much, we can get more 43 db suppression of the
harmonics. If  you guys agree to this , then, I propose as follows :
  1st filter for 3.5 MHz
  2nd filter for 7-10 mhz
  3rd filter for 14-18 mhz
  4th for 21-28 mhz
These will have to be three section filters, which is alright. A
1-of-4 decoder like 74LS139 could do the switching with just 2 lines.

2. The switching of the main filters is at variance with this scheme.
so, we will have to use a dedicated line (as we are doing now) to
switch these filters.

3. There is a third line A0 (pin 23) that is unused. this can be used
to switch in a higher bandwidth filter (more than 10 Khz). with this
filter, the broadband audio can be fed to an 'SDR' back-end like
linrad. The serial port can provide the tuning control.

- f

On Sat, Feb 1, 2014 at 7:01 AM, Dan Reynolds <on30ng@xxxxxxxxx
<mailto:on30ng@xxxxxxxxx>> wrote:

     I'm not any kind of an expert but could you use a Microchip
     MCP23017 I/O expander on the 5 V side of the I2C bus. I was
     thinking something like I saw on the Tronixstuff page here:
     Instead of a LED an I/O line could drive a transistor to drive a
     Then the code could "watch" the frequency and as it changes the
     output line for that particular LPF could be switched.

     Or could you use a 74HC595 to accomplish the same thing.

     I was going to approximate the Minima front panel with a bare
     bones Arduino and some parts and see what I could dream up.
     I don't really know what I'm doing. I'm just muddling through
     trying to patch bits and pieces together...

     Dan -- KB9JLO

     On Fri, Jan 31, 2014 at 6:10 PM, Wayne McFee <nb6m@xxxxxxx
     <mailto:nb6m@xxxxxxx>> wrote:

         Hi Mark,

         If the three outputs were set up as you suggest, a Picaxe chip
         could be programmed to control either individual relay driver
         transistors or a relay driver chip like the 2903(?).

         I've been using that arrangement for filter selection  in a
         homebrew rig.

         Or, if one of those output lines could be programmed to output
         a stepped voltage such as that provided by the FT817 for
         bandswitching info, that makes the programming even easier.

         Wayne NB6M

         > On Jan 31, 2014, at 1:24 PM, Mark G0MGX
         <mark.g0mgx@xxxxxxxxx <mailto:mark.g0mgx@xxxxxxxxx>> wrote:
         > Farhan & Team,
         > I can see that we have provision in the schematic for 3
         digital outputs for band selection, but can only see one of
         these (BAND_HI - pin 11 - Arduino D5) being used within the
         function "setBandswitch". It is this function that currently
         selects the LPF used based on frequency.
         > We could set the state of the three outputs based on
         frequency something like this:
         > <Filter Ideas.png>
         > But someone far cleverer than I would need to explain how to
         create relay on/off switching based on the logic states of
          the three lines - I have no idea how to do that!
         > If we were to implement something like this was the
         intention to use these additionally switched filters in RX as
         well as TX?
         > I would be interested in your thoughts and ideas on how you
         saw this working before I head down the wrong road with my
         > Many thanks,
         > Mark
         > G0MGX

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