[minima] Re: Linear Output Filter Switching

  • From: farhanbox@xxxxxxxxx
  • To: minima@xxxxxxxxxxxxx
  • Date: Sat, 1 Feb 2014 15:26:36 +0000

There's something not right about the curve. The stopband is quite nominal. You 
must get atleast 60 db stop-band.

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-----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.
> M
> ------------------------------------------------------------------------
> 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
> Mark,
> 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:
> http://tronixstuff.com/2011/08/26/tutorial-maximising-your-arduinos-io-ports/
>     Instead of a LED an I/O line could drive a transistor to drive a
>     relay(?).
>     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.
> http://tronixstuff.com/2010/04/30/getting-started-with-arduino-chapter-four/
>     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...
>     73
>     Dan -- KB9JLO
>     https://sites.google.com/site/on30ng/
>     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
>         construction!
>         >
>         > Many thanks,
>         >
>         > Mark
>         > G0MGX

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