Apologies, I am having much difficulties with Wiki pages and images; the correct images are now on the page.
http://www.hfsignals.org/index.php/Final_Output_Filters Mark 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 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