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*COMPLETED* simple S meter? for a minerva tropic master - Printable Version

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*COMPLETED* simple S meter? for a minerva tropic master - jcassity - 09-24-2018

maybe i need to do sum searchin eh before i post?   
Naw,, me thinks ill be a brat Icon_smile

I have me a minerva tropic master and armed with some notes i took from a member about how to hand make a BFO , i jumped in.
i quickly realized i dont like my note taking , so i move over to exploring a S Meter mod to this set.

although i know there is a few generation gaps for me to catch up with to get better at working on this tech, i am trying real hard.  My RF skills are all be zilch,  i mean i understand how all this RF stuff operates, i just dont have the experience to understand how it works if that makes sense.  its just like mux / dmux digital tech but on an analog form with all kinds of parts on either end specific to RF.  Ive never had a job where RF was something i visited often enough to end up needing to "know it" well.


when things like this happen to me, i tend to adapt in different solutions that involve using techniques i already know.

Adding an Smeter to my minerva was explored for a few hours last night.
i went in thinking about what i know.
i know :
--that when we tune , signals become stronger or weaker.
--RF signals with respect to the reference IF are being detected, and amplified, passed on down to the speaker.
--the speaker is nothing more than a wound up coil of wire and or an integrated magnet reacting to the signal that was previously amplified.
--there must be a few terminations that are constantly changing in voltage with respect to the peak to peak amplitude of the signal being compared to the IF.
-- i know that as you turn the tuner knob voltages must change.
--an smeter could be described in a basic conversation as nothing more than a meter bridged across a shunt tow which the shunt is constantly bombarded with varying really super low voltage like mili volts.


at this point i have found in the minerva at least six terminals that vary in voltage.
I also found that at my speaker, the mv readings are monitorable.  ive noticed that with the volume set to a reasonable level, for this set it seems that around 20mv means "nothing is there".  When there is  a station, the mv reading could be around 50mv on a weak signal to as much as 500mv on a strong one.
i took my readings with both a analog meter and a digital one and the act of inserting the meters across the speaker had affect on signal reception or audibility.  this got me to thinking................ of something i already know i can do to build a decent Smeter.

I want to tie a millivolt meter across the speaker as a visual indicator of signal strength.


a few links i am using as the "style" i would like.
this must be small
must be a millivolt meter 0-500mv or 0-500-0 etc


this one goes only to 100mv,, i know that strong stations and depending on my vol knob,, it would max out and peg most of the time.
https://www.ebay.com/itm/0-100MV-2A-MILLIVOLT-PANEL-METER-BBC/201933568986?hash=item2f042dbbda:g:grYAAOSwxu5ZJAvn


is there a place i can buy a analog millivolt meter with a wider measurment range?

should i just buy a 10$ cheapy analog meter and gut it and re-box it and make my own by setting it to the proper scale then mount and call it good.?

RE: simple S meter? for a minerva tropic master - jcassity - 09-25-2018

another idea was suggested and i tried it last night.

i put my cheapy 10$ analog meter in series within the area shown on the schematic.
the only odd thing is this particular conductor is a part of the solid #8awg tinned copper **HOT** buss bar system that runs bare everywhere under the set.  

i cut the buss bar just ahead of the TEE in the photo and put my ammeter there.

I am not really sure about this yet but i think it will be a good option.

with my ammeter in place, i power up and all is well.
the ammeter has 10ma, 250ma , 10ua and 50ua scales only.
i tried using the 10ma scale and the needle pegs out... no matter what.
using the 250ma scale with radio on, the needle creeps up to around 35ma.
when i tune to a station and it comes in with strength, the needle reading drops proportionally to somewhere around 20ma.

when i use the speaker terminals with my millivolt meter, the needle is around 20mv with no signal and it proportinally increases with voltage.

in order to use a milliamp meter, i need a scale like 50ma i think.
what it will look like installed is this...
-radio off , needle to the left...
radio on,,, needle to around 75% to 80% to the right.
As a station comes in really good, the "GOOD" indication is when the needle moves to the left!!  kinda backwards from a man/machine visual indication but it is what it is.  all i have to do is redo a background label showing such info.

RE: simple S meter? for a minerva tropic master - jcassity - 09-26-2018

well,,
my plan to gut a cheapy analog meter isnt acceptable.

first off it WILL WORK to use the pieces parts from a cheap analong meter but i dont actually like where it was taking me as far as bulk of parts.


so........ i continue my hunt for something in one box that will do the job

im just looin around right now.. i have no clue how to integrate a real s-meter but im sure theres nothing to it.

so far................

i really like this one,, its small like i want..
https://www.ebay.com/itm/CB-Radio-S-Meter-with-Light-3-stripes-for-power-SWR-and-S-units-29LTD-style/141229106554?_trkparms=aid%3D444000%26algo%3DSOI.DEFAULT%26ao%3D1%26asc%3D20170221122447%26meid%3D55e9fb5eec2c4da4aba0e283a2c91a4f%26pid%3D100752%26rk%3D1%26rkt%3D4%26sd%3D132257845505%26itm%3D141229106554&_trksid=p2047675.c100752.m1982

this one is kinda big but still much smaller than regular power /switch gear panel mounted ones.
https://www.ebay.com/itm/REPLACEMENT-S-METER-POWER-OUT-GALAXY-55-66-99-NORTHSTAR-ETC-NEW/192614114877?epid=2254469304&hash=item2cd8b2263d:g:kX4AAOSwjW5bYPho:sc:USPSFirstClass!25313!US!-1

another tiny one
https://www.ebay.com/itm/WATKINS-JOHNSON-S-METER/263953260634?hash=item3d74d7205a:g:DQUAAOSwS4Nbpzfs

this one's discoloration will kinda match my glass,, slighly yellow"ish"
https://www.ebay.com/itm/ICOM-IC-271-IC-471-S-meter-Power-meter-working-pull/202446172035?hash=item2f22bb6f83:g:QS8AAOSwE8VbptWq



still plugin away on this..

RE: *COMPLETED* simple S meter? for a minerva tropic master - jcassity - 10-03-2018

i got er done, a few pics and a couple vids.

use the needle mechanism from a cheap meter
read its resistance.
insert in series with your B+ main feeder.
power up and observe if the needle pegs out or it does not move.
determine on your own if you need to add a series or parallel resistor to your needle part.

in m case, the needle part reads 348 ohms.
in order to gain control of the needle i had to calibrate down to 4.7ohms.

radio powers up....
needle pegs out 
then it starts to come down to the scale and follow the signal strength.

i used the multi meter ohms graduations on my reused clear cover to help denote signal strength.

the meter i used was 10$.

this method should work with any radio using any cheap analog multi meter.

basically all you are doing is rigging up an "ammeter" cause when your in series with the battery+,

RE: *COMPLETED* simple S meter? for a minerva tropic master - jcassity - 10-03-2018

another picture and a couple vid links



https://www.dropbox.com/s/4296oyqy08ahky9/VID_20180929_191036.mp4?dl=0


https://www.dropbox.com/s/206tcmvy9qekw4u/VID_20181002_210148.mp4?dl=0

RE: *COMPLETED* simple S meter? for a minerva tropic master - jcassity - 10-09-2018

i am moving on to another post here, about integrating a home brew simple BFO. i have notes i took about how to but too much time has passed and i am having trouble interpreting the notes.

this Smeter is working pretty good though so i will likely duplicate it on other sets.

RE: *COMPLETED* simple S meter? for a minerva tropic master - jcassity - 11-13-2018

its been a while now and to the final post on this.

After many hours of use, this rig for the purpose of being used as an Smeter seems to be holding up just fine without failing.

so,, i can wash , rinse and repeat on other sets when i need to.

RE: *COMPLETED* simple S meter? for a minerva tropic master - morzh - 11-13-2018

You do realize, there is B+ exposed at that coil?

RE: *COMPLETED* simple S meter? for a minerva tropic master - jcassity - 11-27-2018

sorry late reply,,,
help me out here............

yes i know B+ is at the coil. i cut the main B+ at the output of the rectifier and put this coil in series so its actually reading the milli-amp draw like an ammeter. So, both sides of the coil are hot,,, both wires are B+ hot.

what are you seeing that i am not? as in what is the issue you see?

RE: *COMPLETED* simple S meter? for a minerva tropic master - morzh - 11-27-2018

Schematic-wise, none. Safety-wise....an exposed hot is inherently unsafe.

RE: *COMPLETED* simple S meter? for a minerva tropic master - jcassity - 11-27-2018

oh, i see, you didn't see the video yet. the pics represent an incomplete project.

thanks , you had me wondering.

RE: *COMPLETED* simple S meter? for a minerva tropic master - EdHolland - 11-29-2018

Icon_thumbup Looks like you have it covered