[minima] Re: Linear Output Filter Switching

  • From: "Wayne McFee" <nb6m@xxxxxxx>
  • To: <minima@xxxxxxxxxxxxx>
  • Date: Sun, 2 Feb 2014 11:08:36 -0800


I really like the five output filter idea, especially if there were code 
changes that could easily be implemented that would allow the individual to 
select whichever fifth band they wanted.

And, those that preferred to use four filters and not go for the extra band 
could still do so.


Wayne NB6M

From: Mark G0MGX 
Sent: Sunday, February 02, 2014 6:54 AM
To: minima@xxxxxxxxxxxxx 
Subject: [minima] Re: Linear Output Filter Switching

Hi Gang

I've completed a proof of concept of the output filters today; it uses a 74141 
as a BCD to individual selection connected to a 74LS00 used as NOT gates or 
inverters for the output lines.

I can control this OK from the Arduino code, so I have ordered some of these 
CMOS 4028s as this has a HIGH output state when an output is selected whereas 
the 74141 is a LOW state when an output is selected (I have used 74141 
previously to ground cathodes of Nixie tubes!). This is the logic of the chip:

So I now wait for the postman before I can complete the filter output stage.

I am thinking that we might like options in the code/filters as it seems to me 
we need to keep the current RX filter selection pin usage, but also use this 
for filter selection. We can go with very simple as suggested by Farhan and 
have 4 filters, or we can have 5 to include either top band or 60M (5MHz).

I will post more when I have the final design and code mods once built and 
tested. I am definitely going with a 3 line BCD output from the Arduino 
processor to select filters based on radio tuned frequency. This will be 
accomplished in the existing function "setBandswitch". Maybe (only maybe) 
something like this:

In the code we will declare three digital outputs (including the existing 
BAND_HI) and set all three each time we change frequency, the state (HIGH or 
LOW) of each output will be dependent on frequency and in accordance with the 
truth table and output usage above.


On 01/02/2014 18:47, Mark G0MGX wrote:

  very good. That CMOS chip used in the link looks the same as the TTL 74141 - 
but I am no expert.

  This does seem to be the way to go

  On 01/02/2014 18:24, mpcharlton@xxxxxxxxxxx wrote:


          Have a look at this halfway down the page...


          G6ZQS G-QRP 2247 

          -------Original Message-------

          From: Mark G0MGX
          Date: 01/02/2014 17:29:09
          To: minima@xxxxxxxxxxxxx
          Subject: [minima] Re: Linear Output Filter Switching

          Isn't this:


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


          On 01/02/2014 15:26, farhanbox@xxxxxxxxx wrote:
          > Mark,
          > 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:
          > http://www.hfsignals.org/index.php/Final_Output_Filters
          > 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 
          > of the software which I can't find a filter designer? I can enter 
          > 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 
          > well as*_ the existing input filter switching just so long as the 
          > 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 
          > 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 
          > 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 
          > lets decide between us how we are going to do this part of the 
          > We could of course go with the idea of a separate amplifier 
          > maybe with the tubes others are suggesting! I've never built 
          > with tubes....
          > Mark
          > G0MGX
          > 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 
          >> 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 
          >> few things here.
          >> 1. Can we make do with just four filters? I have attached a 
          >> of a simulation I ran (both these programs are available on the 
          >> 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 
          >> distort the linear too much, we can get more 43 db suppression of 
          >> 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 
          >> 2. The switching of the main filters is at variance with this 
          >> 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 
          >> to switch in a higher bandwidth filter (more than 10 Khz). with 
          >> 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
          >>      relay(?).
          >>      Then the code could "watch" the frequency and as it changes 
          >>      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...
          >>      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 
          >>          could be programmed to control either individual relay 
          >>          transistors or a relay driver chip like the 2903(?).
          >>          I've been using that arrangement for filter selection  in 
          >>          homebrew rig.
          >>          Or, if one of those output lines could be programmed to 
          >>          a stepped voltage such as that provided by the FT817 for
          >>          bandswitching info, that makes the programming even 
          >>          Wayne NB6M
          >>          > On Jan 31, 2014, at 1:24 PM, Mark G0MGX
          >>          <mark.g0mgx@xxxxxxxxx <mailto:mark.g0mgx@xxxxxxxxx>> 
          >>          >
          >>          > Farhan & Team,
          >>          >
          >>          > I can see that we have provision in the schematic for 3
          >>          digital outputs for band selection, but can only see one 
          >>          these (BAND_HI - pin 11 - Arduino D5) being used within 
          >>          function "setBandswitch". It is this function that 
          >>          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 
          >>          saw this working before I head down the wrong road with my
          >>          construction!
          >>          >
          >>          > Many thanks,
          >>          >
          >>          > Mark
          >>          > G0MGX



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