[minima] Re: Linear Output Filter Switching
- From: farhanbox@xxxxxxxxx
- To: minima@xxxxxxxxxxxxx
- Date: Sat, 1 Feb 2014 15:26:36 +0000
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 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
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 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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