EMRFD Message Archive 15124

Message Date From Subject
15124 2018-10-15 09:02:41 g4jxx True S meter

Is there a way I can use a logarithmic amplifier and comparators for an S meter circuit that displays 6db points on an led bar graph display? I am looking to do this with a HyCas board first followed by other receiver designs.

15125 2018-10-15 09:06:36 Thomas S. Knutsen Re: True S meter
How about using somthing like a AD8307 or similar LOG amplifier, and place it before the IF amplifier? It may need its own fixed gain amplifier to be able to measure low enough. 
This should give a true dB reading of any input power, then you just need to scale it. Schematics are in the datasheets or on internet.

73 de Thomas LA3PNA.

Den man. 15. okt. 2018 kl. 18:02 skrev g4jxx@yahoo.com [emrfd] <emrfd@yahoogroups.com>:
 

Is there a way I can use a logarithmic amplifier and comparators for an S meter circuit that displays 6db points on an led bar graph display? I am looking to do this with a HyCas board first followed by other receiver designs.

15126 2018-10-15 12:50:38 Mike Hadley Re: True S meter

Thanks Thomas.

I see there are multiple options to choose from on ebay. Never having experience with log amps there is so much to learn and so many different devices. I will probably precede this with an AD603.

Mike G4JXX

Sent from my Xperia™ by Sony smartphone



---- 'Thomas S. Knutsen' la3pna@gmail.com [emrfd] wrote ----

 

How about using somthing like a AD8307 or similar LOG amplifier, and place it before the IF amplifier? It may need its own fixed gain amplifier to be able to measure low enough. 
This should give a true dB reading of any input power, then you just need to scale it. Schematics are in the datasheets or on internet.

73 de Thomas LA3PNA.

Den man. 15. okt. 2018 kl. 18:02 skrev g4jxx@yahoo.com [emrfd] <emrfd@yahoogroups.com>:
 

Is there a way I can use a logarithmic amplifier and comparators for an S meter circuit that displays 6db points on an led bar graph display? I am looking to do this with a HyCas board first followed by other receiver designs.

15127 2018-10-15 13:12:27 kerrypwr Re: True S meter
The LM3915 is the "log" version of the LM3914 linear LED-display driver; with suitable scaling of the input voltage, it might do what you want.

I once made exhaust-gas temperature indicators for racing two-stroke engines, using the LM3914; it was a useful little "sideline" source of income.

Kerry VK2TIL.
15128 2018-10-15 16:09:40 Mikele 9a3xz Re: True S meter
My english is not good but see the story of wb9jps on the net, when he was bild one nice receiver.73 de 9a3xz

pon, 15. lis 2018. 18:02 g4jxx@yahoo.com [emrfd] <emrfd@yahoogroups.com> je napisao:
 

Is there a way I can use a logarithmic amplifier and comparators for an S meter circuit that displays 6db points on an led bar graph display? I am looking to do this with a HyCas board first followed by other receiver designs.

15129 2018-10-15 16:10:29 Mikele 9a3xz Re: True S meter
Maybe this info,help you dear friend...


pon, 15. lis 2018. 18:02 g4jxx@yahoo.com [emrfd] <emrfd@yahoogroups.com> je
napisao:

>
>
> Is there a way I can use a logarithmic amplifier and comparators for an S
> meter circuit that displays 6db points on an led bar graph display? I am
> looking to do this with a HyCas board first followed by other receiver
> designs.
>
>


[Non-text portions of this message have been removed]
15130 2018-10-15 16:11:17 Michael Hadley Re: True S meter
Thanks Kerry, I will take a look at the data sheet. It's probably a cheaper option than the ad607. as well although I think a good linear amp ahead of this is essential.

Mike G4JXX

15131 2018-10-15 16:13:13 Michael Hadley Re: True S meter
Hi again Kerry.

Just had a look at the datasheet and it shows that it operates on 3db (power) increments. With my S meter this needs to be 6db (voltage) increments. Am I missing something here?

Mike G4JXX

On Mon, 15 Oct 2018 at 22:45, Michael Hadley <mhadley157@gmail.com> wrote:
Thanks Kerry, I will take a look at the data sheet. It's probably a cheaper option than the ad607. as well although I think a good linear amp ahead of this is essential.

Mike G4JXX

15132 2018-10-15 19:03:54 kerrypwr Re: True S meter
G'day Mike.

I hate the use of dB in relation to voltage and never use it but it is used in S-units so we are stuck with that.

For, say, 1 - 0v input range, the LM3915 will provide outputs in the sequence 1v, 0.71v, 0.5v, 0.35v, 0.25v, 0.18v, 0.13v, 0.09v, 0.07v, 0.05v, 0.35v & 0.25v.

If we scale this to the S-unit scale, starting with S9 = 50 uV  (I have done the arithmetic in this post in my head and have rounded the numbers) we find that the output sequence is 50uV, 36uV, 25uV, 18uV, 13uV, 9uV, 7uV , 5uV 3.5uV & 2.5uV; each LED is a half S-unit.

The LM3915 is simple to cascade so two would do the job; if half-points are not required, just omit every second LED.

S9 + 10 is out of the 6dB sequence but could be accommodated with a very simple circuit and a separate LED.

The LM391x is really simple; this is the circuit of my temperature gauge;


and this is one fitted to a racing Kart;


Very high brightness LEDs were a novelty 20 years ago and the display had to be visible in sunlight so separate LEDs were used instead of a bar display.

Kerry VK2TIL.

15135 2018-10-16 01:29:24 gi0gdp Re: True S meter
Iam sure there are BUT the AD8307 on its own is not the way to go. If you use this it will probably read 
full scale most of the time as the CIO leaks into it or other band setting oscillators. Its neat but not easy to implement in this application, remember its almost DC to 500 MHz in bandwidth.
cheers
Geoff
GI0GDP

15136 2018-10-16 02:18:49 Ashhar Farhan Re: True S meter
the hycas feedback has itself provided you a logrithimc tap point. here is what you do:

1. tap the Vdetector (across the 0.01u C15 capacitor) to arduino's analog port. (You may have to use some isolation - a differential FET, constant current pair is recommended).
2. With a known signal in the input and a step attenuator, read the readings off the arduino to make a 10 or 20 point map of readings vs dbm. when a signal falls between two readings, do a straight line approximation. it should be good enough.

If you really want the big deal, you will have to tap the signal before the Hycas, feed it to a constant gain amp, filter it and then feed it to an AD8307/AD8310. write the 6b to S-unit conversion software.

I feel that the S units are very subjective reading. it is best to read the signal channel power in dbm. 

- f


15137 2018-10-16 06:48:25 John Levreault Re: True S meter
The 3915 is pretty much unobtanium these days. Maybe you can find it on ebay or
alibaba.

Just FWIW, I needed a bar-graph for a work project. I was able to "clone" the
3915 very inexpensively with a couple of LM339 quad comparators and a string of
resistors. This also allows you to choose your steps, so 6dB/step isn't a problem.

Another option that I considered was using a small cheap micro with an internal
A/D. But the comparator/resistor circuit was cheaper and didn't need firmware
development.

John NB1I


15138 2018-10-16 09:29:32 Mike Hadley Re: True S meter

Hi Kerry.

I think this is the way to go for a general purpose S meter. I will try this by taking the IF out signal after the post IF filter, feed it through a linear op amp then to the lm3195s.

Every other output for the display was an obvious choice easily overlooked.

Mike G4JXX

Sent from my Xperia™ by Sony smartphone



---- planningpower@iprimus.com.au [emrfd] wrote ----

 

G'day Mike.

I hate the use of dB in relation to voltage and never use it but it is used in S-units so we are stuck with that.

For, say, 1 - 0v input range, the LM3915 will provide outputs in the sequence 1v, 0.71v, 0.5v, 0.35v, 0.25v, 0.18v, 0.13v, 0.09v, 0.07v, 0.05v, 0.35v & 0.25v.

If we scale this to the S-unit scale, starting with S9 = 50 uV  (I have done the arithmetic in this post in my head and have rounded the numbers) we find that the output sequence is 50uV, 36uV, 25uV, 18uV, 13uV, 9uV, 7uV , 5uV 3.5uV & 2.5uV; each LED is a half S-unit.

The LM3915 is simple to cascade so two would do the job; if half-points are not required, just omit every second LED.

S9 + 10 is out of the 6dB sequence but could be accommodated with a very simple circuit and a separate LED.

The LM391x is really simple; this is the circuit of my temperature gauge;


and this is one fitted to a racing Kart;


Very high brightness LEDs were a novelty 20 years ago and the display had to be visible in sunlight so separate LEDs were used instead of a bar display.

Kerry VK2TIL.

15139 2018-10-16 09:30:21 Mike Hadley Re: True S meter

Hi John.

The use of comparators was my original thought. I have got some 3915s on order but to keep the board size down the lm339s can be smd's whereas 3915s are dil only. I will try both and see what happens.

Mike G4JXX

Sent from my Xperia™ by Sony smartphone



---- John Levreault jlevro@comcast.net [emrfd] wrote ----

 

The 3915 is pretty much unobtanium these days. Maybe you can find it on ebay or
alibaba.

Just FWIW, I needed a bar-graph for a work project. I was able to "clone" the
3915 very inexpensively with a couple of LM339 quad comparators and a string of
resistors. This also allows you to choose your steps, so 6dB/step isn't a problem.

Another option that I considered was using a small cheap micro with an internal
A/D. But the comparator/resistor circuit was cheaper and didn't need firmware
development.

John NB1I

15140 2018-10-16 09:31:25 Frank Dinger Re: True S meter
The 3915 is pretty much unobtanium these days. Maybe you can find it on ebay or
alibaba.
=========================
Just bought 5 pcs on e-Bay ,all for approx  GBP 2.00  and don't expect these to be fake .
As an S-meter using 2 units after a scaled linear opamp, I intend continuing with 6 dB steps beyond S9  and report signal strength according . At least it will be a  QSO topic for discussion................Oh yes !
Still have to measure current AGC signal inputting  the receivers S-meter ...and hope it is reasonably linear with receiver input signal .........study subject .
Do have a RF signal gen. with attenuator to microvolt level and 50 Ohm output.

Frank  , EI7KS


15141 2018-10-16 09:38:17 John Levreault Re: True S meter
That was one of my considerations as well. We had a height restriction, and even
the SM 3914's are quite tall! The 3915 was a great part; wonder why they
abandoned it. ($$?)

Good luck!

JL


15142 2018-10-16 10:39:09 Roelof Bakker Re: True S meter
Hello all,

Nearly 30 years ago I have build a 'real' S-meter for a DC-receiver using 12 opamps (3 x
TL084). The logamp had 9 stages with 10 dB gain each and a total range of 90 dB.
It was calibrated for -121 dBm (S-0) to S9 + 30 dB.
The analogue meter had a calibrated dial and each S-point was correct +/- 1 dB.

I now own a PERSEUS SDR with an S-meter reading in dBm, which has been very educational in
understanding receiver noise floor in regard to band noise.

73,
Roelof Bakker, pa0rdt
15143 2018-10-16 10:41:42 Dana Myers EOL of some Nat Semi/TI bipolar ICs (was Re: [emrfd] Re: True S mete
15144 2018-10-16 11:06:43 arfghans Re: True S meter
AD8307-based S meter for the R2Pro. Analog meter, of course. I published it in QST, Feb. 2008.

http://wb9jps.com/Gary_Johnson/S_Meter.html

-Gary NA6O

---In emrfd@yahoogroups.com, wrote :

How about using somthing like a AD8307 or similar LOG amplifier, and place it before the IF amplifier? It may need its own fixed gain amplifier to be able to measure low enough. 
This should give a true dB reading of any input power, then you just need to scale it. Schematics are in the datasheets or on internet.

15145 2018-10-16 11:09:15 Bill Carver Re: True S meter
I'm using linear Chinese "BARMETER" displays off eBay.  Searching was a bear, finally found them again using "LED BARGRAPH METER". Their eBay listing is for just one of their displays, they make log/audiophile scaled units, and linear 0-5V DC which I use, a wide range of bar count and size, selectable color, single and dual side-by-side displays. I used a dual 30-bar display for fwd/reverse power on the SDR, later went back and got taller 51-bar displays for a 2 x BLF188XR amplifier. Good products, VERY bright. I have no pecuniary interest, just a satisfied user.
W7AAZ

15146 2018-10-16 11:20:18 Dana Myers Re: EOL of some Nat Semi/TI bipolar ICs (was Re: [emrfd] Re: True S
15147 2018-10-16 11:34:59 Mikele 9a3xz Re: True S meter
Gary, can i find that sheme
15148 2018-10-16 11:46:43 Lasse Moell Re: True S meter
Mikele,
the schematic is on the webpage... if you look at the right upper side, there is an icon saying "Schematic"
Click on it and you will see the schematic!

/Lasse SM5GLC
16 oktober 2018 20:13:49 +02:00, skrev Mikele 9a3xz socijalizam1@gmail.com [emrfd] :
 


Gary, can i find that sheme
15149 2018-10-17 09:10:15 Mikele 9a3xz Re: True S meter
thank you soo much.

uto, 16. lis 2018. u 20:50 'Lasse Moell' lasse.moell@webdog.se [emrfd] <emrfd@yahoogroups.com> napisao je:
 

Mikele,
the schematic is on the webpage... if you look at the right upper side, there is an icon saying "Schematic"
Click on it and you will see the schematic!

/Lasse SM5GLC
16 oktober 2018 20:13:49 +02:00, skrev Mikele 9a3xz socijalizam1@gmail.com [emrfd] <emrfd@yahoogroups.com>:
 


Gary, can i find that sheme
15150 2018-10-17 11:29:03 Nick Kennedy Re: True S meter

I'm not sure if it's been mentioned in this long thread, but there was an S-meter design by W7ZOI posted as an addendum of sorts to the original Hycas article.  I'm sure it won't give the log-linear behavior the OP is after, but I hope to eventually add one to my Hycas receiver just so I can see the meter bounce around.


73-

Nick, WA5BDU

15151 2018-10-18 09:16:34 Mike Hadley Re: True S meter

Hi Nick.

I have seen this circuit from Wes and know it works well. My idea was to come up with a circuit that is simple, easily reproducable and gives proper display of S units. Many builders are happy to see bouncing needles and often give perceived rst reports from ear. A true S meter would help confirm this and when built with a bargraph display less room is taken up on a front panel.

Mike G4JXX

Sent from my Xperia™ by Sony smartphone



---- Nick Kennedy kennnick@gmail.com [emrfd] wrote ----

 


I'm not sure if it's been mentioned in this long thread, but there was an S-meter design by W7ZOI posted as an addendum of sorts to the original Hycas article.  I'm sure it won't give the log-linear behavior the OP is after, but I hope to eventually add one to my Hycas receiver just so I can see the meter bounce around.


73-

Nick, WA5BDU