[minima] Re: Linear Output Filter Switching

  • From: Mvs Sarma <mvssarma@xxxxxxxxx>
  • To: minima@xxxxxxxxxxxxx
  • Date: Thu, 13 Feb 2014 20:19:20 +0530

Thanks fir the article.
  Request little clarification.

1. how come they talk of second harmonic tuned filter.
 perhaps we get third harmonic in general.

2. won't  T37-6  toroids saturate when we have to use the filter with
higher gain amplifiers?

thanks again

On Thu, Feb 13, 2014 at 8:08 PM, Mark G0MGX <mark.g0mgx@xxxxxxxxx> wrote:

>  There's a useful article on these filters here:
>
> http://www.arrl.org/files/file/Technology/tis/info/pdf/9902044.pdf
>
> Mark
> G0MGX
>
>
> On 13/02/2014 08:35, Mark G0MGX wrote:
>
> Hi Gang
>
> I'm back from my whistle stop tour of the Middle East! Just before I left,
> Practical Wireless fell through the letter box; inside was an article that
> included this:
>
>
> So in an attempt to find a 30MHz LPF that looks like its going to work
> well, I've built the one from this table. The sweep looks like this:
>
>
>
> Much better than anything else I have made - I think I am going to try
> using this kind of filter as my output LPFs.
>
> Mark
> G0MGX
>
> On 07/02/2014 19:36, Mark G0MGX wrote:
>
> Well,
>
> I've had my first bash and it looks like this:
>
>
>
> The filters, from left to right in the photo are, 4M, 11M, 19M & 30M. I
> have the test software I linked to the Wiki running that was written to
> flash LEDs connected to the 4028, so each filter is being engaged for 2
> seconds, then the next one switches in for the same and on it goes. The 4M,
> 11M and 19M look fine on the SA but the 30M is way out of bonk. There's
> about 15dfB attenuation at 30M and a very poor slope. It's just really
> pants!
>
> The switching circuitry is the 4028 plus one of those Darlington DIL
> thingamabobs that I mentioned in the email below.
>
> So, any suggestions over what's up with my 30M filter? Inductors are 10
> turns T37-6, 11 turns T37-6, 10 turns T37-6.
>
>
>
> Mark
> G0MGX
>
>
> On 06/02/2014 18:31, Mark G0MGX wrote:
>
> I'm going to have my first bash at the filters and switching tomorrow; I
> only have some tiny single pole relays plus small ceramic caps - we shall
> try that first and see what we see!
>
> I'll definitely be using a bigger than needed DIL socket for the CMOS
> chips! I've also got some of those Darlington transistor pairs in a DIL
> package that was suggested as the drivers (ULN2803A) so will try them too.
> Also I hadn't considered that we don't need to switch the lowest frequency
> filter so lots learned and lots to play with!
>
> Unfortunately I'm off to the Middle East on Saturday morning for a week or
> so, which means I'm running out of play time :-(
>
> Mark
>
>
> On 06/02/2014 18:25, Wayne McFee wrote:
>
> Hi Dan,
>
>  Sure you can definitely use single poles and lower value caps for lower
> power.
>
>  But it doesn't cost much more to build the output filters for higher
> power than you think you are going to use, so that you don't have to
> rebuild them when you want to switch out your lower power amp for another
> one.
>
>  Actually the 200V caps should be good for up to 20-25 Watts, for 50
> watts they should be higher yet, say 500V units.
>
>  But it is all up to the individual builder, and this is really a neat
> project for experimenting and hacking.
>
>  I'm really enjoying all the comments,
>
> Wayne
>
> On Feb 6, 2014, at 9:46 AM, Dan Reynolds <on30ng@xxxxxxxxx> wrote:
>
>   Great work Mark. That will get me started for sure. My Si570 should be
> here today.
>
>  Wayne, I think it's a good idea to double the contacts for higher power
> but I'm probably not going to have a power amp higher than 10 watts or so.
>
>
>  73
> Dan -- KB9JLO
> https://sites.google.com/site/on30ng/
>
>
> On Thu, Feb 6, 2014 at 5:52 AM, Mark G0MGX <mark.g0mgx@xxxxxxxxx> wrote:
>
>>  Hi Team
>>
>> I've done a bit more work on the output filter switching using a 4028
>> (which arrived today!).
>>
>> The wiki is updated:
>>
>> http://www.hfsignals.org/index.php/Final_Output_Filters
>>
>> Including a link to a simple sketch to try and illustrate how it works
>> and enable others to prototype the ideas as I have.
>>
>> There will be more on this topic from me....
>>
>> Mark
>> G0MGX
>>
>
>
>
>
>


-- 
Regards
Sarma

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