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
