[minima] Re: Linear Output Filter Switching

  • From: Mark G0MGX <mark.g0mgx@xxxxxxxxx>
  • To: minima@xxxxxxxxxxxxx
  • Date: Sat, 01 Feb 2014 18:47:03 +0000

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 <mailto:mark.g0mgx@xxxxxxxxx>
/*Date:*/ 01/02/2014 17:29:09
/*To:*/ minima@xxxxxxxxxxxxx <mailto: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 to
individual relays controlling filters?
On 01/02/2014 15:26, farhanbox@xxxxxxxxx <mailto: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 <mailto:mark.g0mgx@xxxxxxxxx>>
> Sender: minima-bounce@xxxxxxxxxxxxx <mailto:minima-bounce@xxxxxxxxxxxxx>
> Date: Sat, 01 Feb 2014 13:47:38
> To: minima@xxxxxxxxxxxxx <mailto:minima@xxxxxxxxxxxxx><minima@xxxxxxxxxxxxx <mailto:minima@xxxxxxxxxxxxx>>
> Reply-To: minima@xxxxxxxxxxxxx <mailto: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 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....
> Mark
> 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> <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>
>> <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>
>>      <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> <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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