[minima] Re: Linear Output Filter Switching
- From: Dan Reynolds <on30ng@xxxxxxxxx>
- To: minima@xxxxxxxxxxxxx
- Date: Thu, 13 Feb 2014 14:40:39 -0600
Mark, thanks. A buddy and I worked on the 'logic' and code for the BCD-7
segment decoder chip. Actually he worked more - I watched... I didn't have
the same decoder chip you had but it was a CMOS one in the same family. It
had the extra lines for lamp test and freeze, etc. Which I don't want but
that's the chip I had on hand.
I've got that code at home and I'll share it. I might just send it to you
and you can decipher it and see if it is worth sharing with the general
public.
I decided to 'splurge' and instead of wiring up individual relays I bought
some of those relay boards you can get to use with microcontrollers. They
even have optop isolated inputs! And from flea-bay they are super cheap.
They are 5V coils but I can't see how that would matter.
73
Dan -- KB9JLO
https://sites.google.com/site/on30ng/
On Thu, Feb 13, 2014 at 9:37 AM, Mark G0MGX <mark.g0mgx@xxxxxxxxx> wrote:
> Some comments below:
>
>
>
> On 13/02/2014 14:49, Mvs Sarma wrote:
>
> Thanks fir the article.
> Request little clarification.
>
> 1. how come they talk of second harmonic tuned filter.
> perhaps we get third harmonic in general.
>
>
> *The second harmonic is more attenuated than conventional LPF; the third
> and higher harmonics will be the same as conventional - these filters have
> steeper cut off slope.*
>
>
>
> 2. won't T37-6 toroids saturate when we have to use the filter with
> higher gain amplifiers?
>
>
> *Yes, if you look here http://www.gqrp.com/technical2.htm
> <http://www.gqrp.com/technical2.htm> you will see different cores
> recommended for different power levels.*
>
>
>
> 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
>
>
>
>
Other related posts:
