SINAD Meter - Home Made for £15.
 

Hello

I have been trying to get hold of a Sinad meter for a while now to setup and test my large collection of CB radios and ham radio gear, problem being that they dont show up for sale very often and when they do they are often in the states which attracts high shipping and duty costs, not to mention many dont work properly and need new capacitors and significant maintenance to work correctly, there is a fellow on youtube who repairs one and shows it at the end "working" when it actually isnt working ???

I posted a request on here for a meter in the wanted section with some helpful links suggested by some users, I tried the software versions of all types but there is significant hysteresis and lag which makes them very cumbersome to use, you after all cannot replicate the speed of a true analogue signal in real time without any conversion.

Inspired by the very helpful Wendymott a user on here who supplied me with some very useful information i started the build.

I already had vero board in stock, I picked up a pack of LM348N op amps from ebay for 2 pounds and a single 2N3819 J-Fet for the AGC part of the circuit, I already had the transistor in stock.

All the other components I had in the shack trays, I used 1% tolerance resistors and I matched the capacitors in the 1Khz notch filter to ensure it balanced properly, took about half a day to build the board and another half a day to find my faults, mostly not breaking the tracks on the back of the board.

Once built I tested the board using my dual channel scope and signal generator and got a lovely tight band block at 1Kz, so then I moved on to the case.

I designed the case in Design Spark, a free download from RS in the UK, really nice and easy program to use, the only other item I had to design the case around was the meter, I picked up a 200V moving coil meter from Amazon for 6 pounds, I removed the large series resistor, copied the scale from the Original Sinadder and printed it off, you can see on the back of the meter the offset adjustment pot I calibrated it with, meter with resistor removed was 0.5V FSD.

Just for fun I popped the original logo on the front of the case as this circuit is based on the Sinadder 3 original circuit without the analogue volt meter switch as I didnt need that facility, so i have a basic 3.5mm Audio jack on the side, an Illuminated orange push button on the top and the meter, all runs off my 12V bench supply, the illuminated button draws more current than the circuit does.

Before anyone asks its orange because I needed to use up the reel of plastic on my 3D printer as it was getting old and needed using up, besides I wont lose it now.

I have been testing it for a day or so and it works absolutely superb and matches all the software versions without the annoying lag, such a very useful tool to use for alignment.

I only built the AGC section, the filter and the rectifier to drive the meter, I also popped in the voltage divider circuit and supply capacitors as well as the Op Amps are dual rail.

Hope that inspires others to give it a go, it takes up very little room on the bench and I think it looks rather jolly as well, any questions I am happy to answer them.

Re: Sinad Meter - Home Made for £15
 

looks nice. Well done!
SINAD is what I used back when repairing pmr gear a couple of decades ago.
My meter is from a factory and made by their own test gear engineering department.
Rob

Re: Sinad Meter - Home Made for £15
 

Cheers

Yes I am very happy with it, once you have used one to align a receiver you sort of never trust just your ear although you do need to use both ha ha.

Yes a lot of modern test sets have this function built in but not all are analogue and many are very expensive indeed, you dont need hi fi levels of THD accuracy here in CB and ham radio world so these are just fine for that.

Re: Sinad Meter - Home Made for £15
 

That is a very nice job!

If you could message me a cct. I will knock one up, have plenty of spare meters.

TY;D

Re: Sinad Meter - Home Made for £15
 

Hi

Yes the circuit is the same as the one that is in the Sinadder-3 manual which you can download here

The only thing you have to watch is note that the symbol for ground and the symbol for the negative rail to the op amps is similar, watch that you don't get them mixed up.

Re: Sinad Meter - Home Made for £15
 

Rather ironically, most distortion meters, when measuring THD actually measure (THD + noise) to (signal + THD +noise). So long as the signal is sufficiently larger than the noise and THD terms, what you get is SINAD but expressed as a percentage not in decibels. So 1% indicated distortion is 40dB SINAD. 3.16% is 30dB. 10% is 20dB. Above this an error creeps in to the simplified arithmetic, but you can calculate a look-up table to correct for it.

So any distortion meter can be used as a SINAD, with a conversion chart for the results. But without the AGC function, you'll have to keep resetting the FSD on signal knob every time the level changes.

David

Re: Sinad Meter - Home Made for £15
 

And lots of distortion meters, including my HP 334A, read out directly in dB anyway. Handy.

Chris

Re: SINAD Meter - Home Made for £15.
 

A very quick video demo in laymans terms of it working for those interested and a link to the meter that I used.

https://youtu.be/Z81u_GHf-M4

https://www.amazon.co.uk/gp/product/...?ie=UTF8&psc=1

Re: SINAD Meter - Home Made for £15.
 

Hi Knoxieman.. Glad to be of help :D

Re: SINAD Meter - Home Made for £15.
 

Hi Wendy

Yes thanks you were a great help and inspiration, thanks again, such a useful little meter.

Paul

Re: SINAD Meter - Home Made for £15.
 

Nice homebrew meter. I made a Sinad meter from an old Radcom article by Ed Chicken. Spent ages looking for one so built my own, then managed to get hold of a Sinadder 5. Both very similar in operation.

Regards
Teabot

Re: SINAD Meter - Home Made for £15.
 

Yes they very rarely come up for sale, now I have a real sinad meter if find my home made.one to be spot on, I've changed the capacitors in the original sinad meter and calibrated it and both meters are the same,.my own meter is more responsive and reacts quicker.

Re: SINAD Meter - Home Made for £15.
 

Hi!

My apologies for asking silly questions, but can you tell me the f.s.d. of the meter you used in your home–made SINAD meter – the f.s.d. current doesn't seem to be quoted in the bookwork!

Chris Williams

Re: SINAD Meter - Home Made for £15.
 

Hi

It wasn't very much, I can't remember exactly, I used a pot inline to wind it back prior to calibration, I'm going to re calibrate it this week if get time then I will measure it, it's amazing how well it works ��

Re: SINAD Meter - Home Made for £15.
 

Is there a circuit or info? I'd like to try and build this SINAD Meter, could some one email me all the info I need please.

Thanks very much.

Re: SINAD Meter - Home Made for £15.
 

Dave.. Just google Motorola Sinad meter... or PM me with your email address.

Re: SINAD Meter - Home Made for £15.
 

Hi Could you please send me the info to my email.

email addressremoved by moderator

Thank you so much
Andy M
M0FAT

Re: SINAD Meter - Home Made for £15.
 

I thought it might be interesting to have a go at generating a fairly accurate 12dB SINAD calibration signal to test a typical SINAD meter. I've captured this in a wav file that has a 1kHz tone and flat noise out to about 6kHz. I did it using hardware rather than in DSP so the accuracy won't be quite as good as a DSP version but I think it should be good enough to do an initial test on an analogue SINAD meter.

The idea is to play the wav file back to your meter via your PC sound card and see how close the SINAD measurement is. I've tried to get within 1Hz of 1kHz but the accuracy of my soundcard (and yours) will have some impact on this. The wav file has a 1kHz test tone that will hopefully be within 1Hz of 1kHz on a typical soundcard. The noise is flat out to about 6kHz and then drops away fairly steeply.

The wav file is about 1 minute long. The first 10 seconds are tone + noise to allow a 12dB SINAD measurement. Then the next 10-20 seconds are noise only. Then the tone and noise are back for 10 seconds followed by just noise for about 10 seconds. Then it is tone and noise again followed by the last 10 seconds that are tone only.

This last 10 seconds should give a high SINAD reading. Probably >50dB.

Here's a link to the wav files

https://www.qsl.net/g/g0hzu//RF%20Tr...%20data/SINAD/

There are also wav files for 15dB and 20dB SINAD but I wouldn't treat any of these as being 'very' accurate. I'd like to think they are all within +/- 0.5dB but a SINAD signal can be tricky to set up accurately using analogue hardware. Lot's to potentially go wrong here...

If your meter doesn't give a 12dB reading then it could be because your meter has a null that isn't centred on exactly 1kHz. Also, the Sinadder type meters use an averaging detector and the 1kHz notch won't be perfectly narrow. I think the averaging detector under reads noise slightly and the less than perfectly narrow notch filter makes it over-read slightly. So it might cancel out and give a reading close to 12dB SINAD..

The on/off keying every 10 seconds also allows a regular (S+N)/N check using a true rms voltmeter or a modern scope. The reading will be slightly higher than 12dB when measuring (S+N)/N but only by a fraction of a dB. Sadly, my EeePC laptop does introduce some low level spurious during the recording process but these are at very low levels. You can check this out using a spectrum analyser program and a PC soundcard.

Re: SINAD Meter - Home Made for £15.
 

If you calibrate the ref level of a true rms voltmeter to the last ten seconds where it is tone (and no noise) it should be possible to measure the signal to noise ratio as well. You just have to wait until there is noise only and then you will be comparing the clean noise free signal to just the noise.

Ideally this should show a 12dB ratio on a true rms meter as long as it has a flat bandwidth of more than about 10kHz.

The aim of the on/off keying every 10 seconds is to allow SINAD and (S+N)/N and also S/N measurements to be made from the same wav file.

Re: SINAD Meter - Home Made for £15.
 

Video of the build process and operation here along with download link with all of the files you need to make your own version of the meter, link to download in the video description.

https://youtu.be/tMk2hL3j5rk