17-11-2024, 07:48 PM
I have finally completed my little attenuator.
It has taken a while as my first attempt, using wired resistors, had an issue with the 20dB module. I found that my design did not lend itself to easy investigation and as I had already visualised a better approach using surface mount components I decided to replace the internal circuitry. It was not as difficult as it may have been because I could use the existing box, complete with sockets and switches in their original positions.
The new internal circuitry is shown (see photograph) along with an external view.As can be seen, all components on the board are readily accessible.
In this design I have used series resistors in all positions. It may well be possible to purchase exact values as the requirements for 50 ohm resistance (impedance) matching are well defined but I only needed to buy a small number of values if I used the ones I already had. I show my rough sketch indicating the resistance combinations I used.
The other table I show is the results I obtained on DC test. I used my (nom) 1.25V DC supply, which I designed and used with rod pentode circuits which is well stabilised. The actual results are slightly out but noting that I have actually used 47 ohm source and load I tabulated the results of using these in LTSpice. Bearing in mind also the slight loss with straight through connection my results seem to tie in well. The only one which is quite a bit out is that for 70dB (all attenuators inline), and this is almost certainly because the output meter was fluctuating between 0.1 and 0.2 millivolts so I took it as being 0.15mV. My meter has 0.1mV as it's bottom limit. I saw no point in increasing the input voltage and risking overloading it.[attachment=22811][attachment=22811][attachment=22812][attachment=22813][attachment=22814]
Both handwritten sheets are those I worked from so rather untidy.
That being completed, my next project, which I am getting on with, is a noise generator which I should be able to use for filter testing. What I needed was a wideband noise, principally, at least at the moment, to cover HF. I have had a noise diode, Semitron type Z1M, for some years, although have no information on it. I have found in "Practical Electronics" circuits using diode type Z1J in a music synthesiser. The Z1J is a lower voltage breakdown avalanche diode as their circuit operates on much lower voltage than the just less than 24V which mine tested at.
I intend to use RF amplifier IC's type MAX2611 which I have bought for amplification and am probably intending to use a bandpass filter to limit bandwidth to that which I need. I have found online a program called "Elsie" which seems to work well enough for me using Wine in Linux. It has a good feature such that a designed circuit can be saved in a format that can be directly read in by LTSpice.
A bit more complicated than an attenuator and will need development testing but I'm progressing.
It has taken a while as my first attempt, using wired resistors, had an issue with the 20dB module. I found that my design did not lend itself to easy investigation and as I had already visualised a better approach using surface mount components I decided to replace the internal circuitry. It was not as difficult as it may have been because I could use the existing box, complete with sockets and switches in their original positions.
The new internal circuitry is shown (see photograph) along with an external view.As can be seen, all components on the board are readily accessible.
In this design I have used series resistors in all positions. It may well be possible to purchase exact values as the requirements for 50 ohm resistance (impedance) matching are well defined but I only needed to buy a small number of values if I used the ones I already had. I show my rough sketch indicating the resistance combinations I used.
The other table I show is the results I obtained on DC test. I used my (nom) 1.25V DC supply, which I designed and used with rod pentode circuits which is well stabilised. The actual results are slightly out but noting that I have actually used 47 ohm source and load I tabulated the results of using these in LTSpice. Bearing in mind also the slight loss with straight through connection my results seem to tie in well. The only one which is quite a bit out is that for 70dB (all attenuators inline), and this is almost certainly because the output meter was fluctuating between 0.1 and 0.2 millivolts so I took it as being 0.15mV. My meter has 0.1mV as it's bottom limit. I saw no point in increasing the input voltage and risking overloading it.[attachment=22811][attachment=22811][attachment=22812][attachment=22813][attachment=22814]
Both handwritten sheets are those I worked from so rather untidy.
That being completed, my next project, which I am getting on with, is a noise generator which I should be able to use for filter testing. What I needed was a wideband noise, principally, at least at the moment, to cover HF. I have had a noise diode, Semitron type Z1M, for some years, although have no information on it. I have found in "Practical Electronics" circuits using diode type Z1J in a music synthesiser. The Z1J is a lower voltage breakdown avalanche diode as their circuit operates on much lower voltage than the just less than 24V which mine tested at.
I intend to use RF amplifier IC's type MAX2611 which I have bought for amplification and am probably intending to use a bandpass filter to limit bandwidth to that which I need. I have found online a program called "Elsie" which seems to work well enough for me using Wine in Linux. It has a good feature such that a designed circuit can be saved in a format that can be directly read in by LTSpice.
A bit more complicated than an attenuator and will need development testing but I'm progressing.
