Grant 2 deviation

[delboyonline]

Has anyone tried to turn up the FM modulation on their Grant 2 yet?

[Tarambor]

Knights do it to every new set they sell apparently.

[Warden]

Knights do it to every new set they sell apparently.

Yes and they turn the power up. Mine is doing 6 watts FM.

[Tarambor]

Yes and they turn the power up. Mine is doing 6 watts FM.

Thats a pity. An extra couple of watts isn't worth the effort but I'm sure it could cause a problem if you wanted to use a linear because most I've seen are 4w in.

[Mudslinger]

Most of the bigger linears are 10W in on AM/FM and 20W on SSB

The smaller ones that do 25-35w with 4w in are not really worth the hassle anyway in my humble opinion. Especially as something like a KL-203 is only about £50 or so new.

[mickymcd]

Ive adjusted the FM deviation on mine today its set pretty low on mine id say at 9 oclock so I adjusted it to 11 vast improvement using stock mic I use mine in conjuction with a kl203 works great power wise not going to be adjusting alc etc

[Mudslinger]

They are probably set on the low side at the factory to make sure that they meet the spec. The Spec is +/- 2KHz which is pretty low anyway.

(CB 27/81 was +/- 2.2Khz IIRC)

[Tarambor]

That guy on Youtube who does the CB repairs sets them to 2.5kHz which is standard for narrow FM mode.

Found his videos this week...

https://www.youtube.com/channel/UC6w677 ... 2VxqZk-UlA

[delboyonline]

Ive adjusted the FM deviation on mine today its set pretty low on mine id say at 9 oclock so I adjusted it to 11 vast improvement using stock mic I use mine in conjuction with a kl203 works great power wise not going to be adjusting alc etc

Can you tell us which pot to adjust?

[andrew013]

it says dev for devation

[Warden]

You will need good eyes and a small trimming tool.

[delboyonline]

it says dev for devation

I did notice that pot on a photo of the board but just wanted to see if anyone had actually tried it?

[rpcomms]

Most of the issues related to user sounding low is not the deviation setting,its the other person radio kit either being old school,ham hf or old 27/81
All the new multi norm cb are set up on super narrow not ham/commercial narrow,difference being the channel spacing fm system design for
All ham /commercial kit is generally set up for 12.5 or 25khz spacing
Cb system is 10khz spacing
The cb fm detector chip is set up for 60% deviation at 1.2khz deviation
Ham/pmr is set up 60% deviation at
1.5khz fm narrow
3.00khz fm wide
The multi norm sets have a slightly more gain in audio,where ham/pmr have less,so when your receiving on ham hf rigs they sound quiet to you,even some of the old school fm cb based on a different fm system
Also the Multi-Norm sets use 9khz bandwidth filters which are lot tighter
So turning deviation level up is a bodge fix,yes it works but your exceeding the 10khz channel bandwidth if you go beyond the 2.00khz max deviation.
Heres the maths

Cb ETSI/EN spec
Max dev 2.00khz
60% of 2.00khz=1.2khz deviation-Fm detector level for full volumee
2.00khz+2.5khz(max audio upper frequency)=4.5khz x2=9khz bandwidth IF filter

Ham/Pmr Fm narrow 12.5khz spacing
Max dev 2.5khz
60% of 2.5khz=1.5khz deviation- Fm detector level full volume
2.5khz+3.0khz(max audio upper freq)=5.5khz x2=11khz Bandwidth IF Filter

Ham/Pmr Fm wide 25khz spacing
Max dev 5.00khz
60% of 5khz dev=3khz-Fm detector level full volume
5khz dev+3.00khz(max upper audio freq)=8khz x2=16khz IF Bandwidth
As you can see if you choose the ham fm systems,yes your multi-norm cb will sound quiet to you as fm detector is slightly less audio gain in the fm detector!
So pumping ur fm dev up beyond the 2.00khz max allowed is not really solving things really
What ive found best way is to alter the fm detector audio gain level on 10m usa exports,ham hf,old school fm to meet the new regs of 60% dev=1.2khz
Set the tx fm max 2.00khz (15khz LPF on dev meter)
That way no splattering of 10khz spacing channels often heard
How to do it?
Two types of fm detectors found in radios'
Coil
Ceramic resonator
Generally they will be a resistor strapped across these devices typical 1k8-3k2 on resonator
And 10-68k on coil types
The resistor value determines the audio gain recovered at 60% deviation level on fm
To up af gain increase resistance value
To reduce af gain reduce value
If you study ham kit schematic this is how they switch audio gain of fm detector when switching wide/narrow fm mode as well as the IF filters! Note the maths above for ref
So to upgrade your set ull need a rf signal gen
The offending set connected up
50uv pd level injected at ant socket
Set radio to narrow fm if hf rig has it or export 10m set
1khz mod on RF sig gen
Scope speaker output (i use 8 ohm 10watt resistive load)
Set radio volume to max,should see a clean clipped sinewave on scope
Now adjust deviation level (1khz -3khz)on rf signal gen until you find where max audio point starts at ie 1.5khz,3khz
You can scope fm detector audio pin and make a note of value ie 1.5khz dev max audiopoint
60mV peak to peak
Next drop dev on rf sig gen to 1.2khz measure af ,if theres a difference ie 30mv difference between 1.2khz and sweet point 1.5khz
Thats the difference you need to pick up in gain.
Increase the resistance value up a bit across coil or resonator to bring audio gain up,recheck test
Also check your headroom by moving dev level on signal gen ideally you looking fora headroom of 1.2khz staring point upto about 3khz
Ive successfully done this mod to FCC spec 10m export radios,ham hf set on fm wide and now used on uk/eu cb super narrow fm system,just recently ranger SS158 and SS3900 and now users on multi-norm radios sound perfect and volume control is not max out struggling and stops the dreaded you sound quiet to me,turn your dev up syndrome heard on air.
I will agree however some mfr are setting too low,fm cb tx dev should saturate at 2.00khz and no more to avoid splatter
Low microphone gain from some fm sets does not drive the fm modulator hard enough ,ive seen that also does not help overall.
And lastly some mfr use the Am agc microphone circuit to soft limit the fm,again not good practise,it should be almost like square wave the fm modulation waveform when clipped hard,thats what gives fm the audio punch!
It should only be a sinewave wave form at 60% deviation,not full dev!
Diode audio clippers tend to work best than the soft agc limit ones

Hope that helps?
And try to keep fm dev narrow for other users ,not to wide on cb,we had a terrible period a year or too ago with this very issues caused a lot of agro,newbies not knowing turn fm dev up way to loud not knowing because some burk told him sound quiet on his 2000k ham hf rig set up on wide fm,the user was so arrogant to fact caused a lot of problems,walk away at some ones else s expensive
If he just set it to narrow it may of helped stop giving out duff info,even technically ham fm narrow not completely right it would have stopped,the chap didnt even know radio could switch!
Yes i did reset the poor newbie cb user radio back to standard fm dev no charge.
Also addition note :some ham kit inc 10m export radios used on fm can be wide fm only so fm cb may sound quiet on them
,some kit can switch wide/narrow fm but does not switch the fm detector chip audio gain!
That one threw me,mainly by a brand called Yxxxx
Biggest problem is very little true info on this subject and sometimes it can become guess work,hearsay, and worst ive seen is some forum sites esp usa with bad terminology used,try it wfm vs nfm of fm wide vs fm
Ive been very fortunate to work on land mobile radio where this is used a lot for export and gov systems fm-w or fm-n repairing equipment,and cb radio,but agree not enough real text book info on subject,even i struggle to get head round it at first esp why they switch audio gain in fm detector!
Hope this help guys get a better understanding of whats going on,oh the old fm uk40 system did use slightly wider fm of 10khz bandwidth/2.5khz dev but that defunct now as most of all new cb kit coming out is etsi/en std based on 2.00khz/9khz b/w
If you want a ref to wide/narr fm ham spec check service manual of icom IC-703 fm chip,look for the 455khz resonator,ull see 2 resistors 3k2 value,one switched via a transistor switch in parallel.
3k2 on own =nar fm high audio 60% dev=1.5khz
3k2 switched in parallel with the other 3k2=1k6 value=fm wide low audio 60% dev=3.00khz

Sorry if typo on a dam touchy pad tablet and msg long,hope this of some use guys and makes sense?

Rob

[Phoenix]

Rob.......as always ,a very good explanation .I have one of your 3900's and that thing rocks.Audio in all modes is superb.

[rpcomms]

No problems,glad your having good results

I have a improved Version 10 Jopix SS3900-EU running and discovered a few more improvements on FM side,some of it related to FM TX and RX to this subject.
Most of the current Multi-Norms CB operate this special extra narrow FM system,its unique and not very well understood or documented well.

Ive also recently discovered something very significant and interesting in last week or so regarding the UPC1028H FM detector chip on this very subject (will release info soon)

Most of the old school CB kit,USA export CB,HF radios with fm-narrow all operate on a wider or slightly wider above the CB fm system,like I explained the FM detector is the issue,not the multi-norm radio,yes it kinda fixes the problems to a user operating this kit when receiving the Multi-Norm cb kit but really this is wrong approach as you can can exceed the 10khz channel bandwidth,plus then make user set of the multi-norm even louder (if dev set excessive) too loud and it all becomes a complete mess on the CB band,as did locally in my area.
Yes defo turn it up to 2.00khz max and no more,when you make the adjustment ensure microphone gain set to max as you want to hard limit the transmitted fm deviation,not soft limit at say 50% microphone gain (hint),always 100% mic gain.

To fix the real issue is a bit involved explanation but basically theirs 3 types of FM detectors used in CB\HF radios

Coil based discriminator with FM detector chip (SS3900,Galaxy,SS360,JFK,Intek handportable series etc)
Ceramic resonator discriminator with FM detector chip (Icom,Yaesu,Kenwood,SS6900,Alico DX135,Licoln V2+)
Coil based Foster Seeley discriminator (Ranger SS158, 2950DX is one) discrete components

to control the recovered audio level of of the fm detector a damping\load resistor is placed across the the fm detector coil,ceramic resonator

Some manufacturers on Ham\Commercial uses will often have a transistor switch to place another resistor in in parallel
when switching Wide(60% dev=3khx Dev System))\Narrow(60%=1.5khz Dev System) FM to alter the audio output level by half for the different FM systems,this is how its done often,it also effects how much audio noise is fed to the noise squelch circuit if used (often cb use the S-meter agc line carrier squelch on fm,not noise squelch),mostly ham\commercial kit.

So by altering the strapped resistor across either version of detection you can change the 60% deviation point.
Reduce resistor value,you have less recovered Audio from detector
Increase resistor value and ull have more Audio gain from detector

Now by injecting a RF signal generator into a FM HF\CB set you can find out by scoping the fm detector audio output pin and by varying the MOD\DEV level range from 1.2,1.5 and 3.0khz deviationlevel on RF signal generator
You can find where the 60% mod level starts and whee maximum Audio recovered gives from speaker outputs into a resistive 8 ohm load.

so lets say I have a Icom IC-703 on bench sent to Narrow -FM (FM system is 2.5khz max dev\9khz [email protected] 60% nominal,i know this by specifications in service manual) and gives 5.5Volts RMS into 8ohms resistor load max volume
This is purely the Rx side we are testing,as we know the TX side is a little high on fm dev 2.2khz (no ctcss) max

I want to check it compatible for 10khz channel spacing
we know from my previous post the max CB fm deviation system is 2.00khz max for 10khz spacing cb system
we know the 60% deviation level is 1.2khz cb system
we know the bandwidth if 9khz for cb system (IF filters fitted inside cb radios generally)

set your fm RF signal generator to operating channel ie 28.100mhz
1khz test tone
set fm dev\mod to 1.5khz (60% level and we know icom is in ham FM narrow mode)
set RF level to -73dBm or 50uV Pd (strong signal)

measure your maximum audio recovered from radio across speaker load say 5.5V RMS thats your ref
measure on FM detector chip the audio out pin on scope say 15mV RMS
now adjust DEV level on RF FM signal generator and resduce your DEV level on RF FM signal generator,while monitoring AF volts on speaker load\fm det Audio pin
If the audio recovered does not change until you hit 1.2khz dev point,your radios fine

If it audio recovered drops quickly below 1.5khz ie 1.2khz dv=5.3V RMS speaker load and 13mV at audio det pin,you need to boost audio back up to same audio level for FM cb system ie 1.2khz(60% fm system)
by 0.2V RMS or 0.2mV at FM detector audio pin as previously measured
This will make up difference to achieve same max audio so stations dont sound low audio to you even when they are using correct legal deviation levels.
(We are trying to get same audio level recovered at 1.2khz cb fm system as you would ham\commercial Narrow Fm system)
If you do require boosting audio up (most cases I found do with a few exceptions) to get compatibility.

It just requires increasing the load resistor either across coil or resonator with a slightly higher value ,thus decreasing the audio load across the coil or ceramic resosnator part,and increasing the recovered audio threshold point of 60% level at 1.2khz fm cb system.

If the audio voltage recovered is fine at 1.2khz as it would at 1.5khz,well no need to alter radio FM detector,any in the case of the Icom IC-703 you dont its compatible (ive checked)

Some ham sets using a ceramic resonator FM det chip MC3361,i have come across on models "Yxxxx" and older HF rigs where
they switch the FM filters or not,
but do not the resistor on the fm detector chip,while technically wrong you have to turn the volume knob up higher on narrower fm systems used on cb
and it causes the "cb fm system to sound a bit quiet"due to the lower transmitted fm deviation used,this is the reason why!

Easy fix just increase the resistor value and that will increase your recovered audio,from say 3khz dev to 5khz dev window onriginally
To ideally want the fm detector window to work from 1.2khz to 3khz deviation coming in for max audio recovery for maxium audio from radio

The lincoln mk1,2+,Alinco DX135 suffers this problem where the resistor value has been set for 60% dev system at 3.0khz or possible 1.5khz,instead of the 60% 1.2khz dev CB system as used on multi-norm CB and Ham 10m EU bands.

check the schematics of the fm detector chip and ull see the value different
Grant 2 EU 3K resistor value correct,CRT 6900 or similar same correct
and say Alinco DX135,thinks its 1K8 (off top of head),same fm chip just resistor value looks a little lower (im gonna be looking at this soon to confirm my curiosity)
the optimum value should be around 3K to 3K2 for cb fm system,often I see 1K2-1K8 in value as is ceramic resonator basedwhich tends to suggest they are set for wider fm system
Coil based around 10K-30K in value

USA uses wide fm on 10m band as per FCC spec,this is one of the reasons why 10M export gear from USA based on wide fm,can sound a little low on EU CB\Ham super narrow FM system due to the fm detector audio recovered for different regional markets.

Its easy to fix once you get head round it.
I have recently fixed this issue with Jopix SS-3900-EU,SS-158EDX and now sound loud recovered audio from a Multi-Norm CB sets on 1.2-2.5khz dev being received to me and no more having to crank up volume control so far at nominal levels.
really clear loud un-distorted audio and now have full voltages at speaker on lower legal fm devs

Plus all my own kit,no need to turn fm devs ups,as long as they meet the 2.00khz max (1khz test tone\speech peaks maybe a little higher) Im happy,ill agree have seen some set a tad low 1.5-1.7khz and would turn these up as discussed here
HINT if checking FM deviation esp the Marc\IFR2995 tests-sets or a modulation fm meter,ensure your 15khz LPF is set,not the 0.3-3.4khz as often used\seen incorrectly used by techs,it will give you the wrong FM deviation value!

The downside is you start to hear all the FM over dev'ers ( fm-wide 4-5khz) with slight distortion on edges of there audio transmissions,but certainly helps now due to most new cb based on a tighter fm spec.

Old school cb can also be altered if recovered audio is a little down at the 1.2khz point,by changing that resistor,often a coil based discriminator,same thing,same method.
Ham HF kit can also be modified this way,but check what filters used in the fm section ideally 9-10khz wide in the 455khz filter
Often the MC3357 fm detector chip used,using a coil based discriminator,a resistor should be seen on schematic strapped across this coil,same method,if you know what fm system its based on to give staring point thats helps then when altering the detector circuit.

Hope this extra info helps and explains one the reasons why operators can sound low audio to you on your radio kit.
Most of the new current Multi-Norm CB sets wont have any of these issues at ALL so no panicking,as thats the fm system radio was designed for and FM detector chips work down to the 60%=1.2khz system
In most cases you can get away with it in practice,at worst maybe need to reduce your TX dev to 2.00max and put up with low recovered audio on cb EU\UK system on your other radio kit listed below,unless want to have a go.


The users who may come across this issue will be
Some HF Radios some wide fm only,some wide\narrow switched but audio gain is not,some wide\narrow is switched including audio,but threshold point will not meet 1.2khz min
Old school export cb kit
Some old legal UK40 kit
10m fm\export band kit USA based.

ideally you ll need a Fm signal generator,scope or RMS voltmeter 8ohm audio dummy load and scope probe or a good tech to do experiments.

Ill come back soon on UPC1028H fm chip discovery very soon WIP and info maybe released elsewhere first.

I may also release mod sheets at some point in pdf format as I come across this issue on bench and check different brands.

The Alinco DX-135UK 10m\CB will hopefully be checked after Christmas against my CRT6900 (which i think is correct) as schematics shows different values on FM chip even thou same chip type im curious,so carry out some tests so and post results.Plus a FT-847 Ill do same checks on as I suspect the FM filters do change in W\N,but not the fm detector audio gain from user reports fed back to me and quick look at schematics,ill check.

Rob