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 Modding a linear the work on SSB (Help Needed) 
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Post Modding a linear the work on SSB (Help Needed)
Morning Hams,

I've got a 2m FM Linear amplifier and I'm hoping one of you can point me in the right direction to make it function on SSB. I've heard it can be done by adding a simple switch and capacitor to trick the amplifier into thinking the carrier is constant as I understand on SSB it goes up and down as you speak. The question is on what part of the circuit do I add this capacitor and switch and what uF value capacitor do I use.

(max output from linear is 30w with a 5w input, I run it with a 1-2.5w input and get around 6-12w out.

Thanks very much in advance,

Nick
M6NDD


Wed May 10, 2017 8:21 am
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 Modding a linear the work on SSB (Help Needed) 
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Post Re: Modding a linear the work on SSB (Help Needed)
M6NDD wrote:
Morning Hams,

I've got a 2m FM Linear amplifier and I'm hoping one of you can point me in the right direction to make it function on SSB. I've heard it can be done by adding a simple switch and capacitor to trick the amplifier into thinking the carrier is constant as I understand on SSB it goes up and down as you speak. The question is on what part of the circuit do I add this capacitor and switch and what uF value capacitor do I use.

(max output from linear is 30w with a 5w input, I run it with a 1-2.5w input and get around 6-12w out.

Thanks very much in advance,

Nick
M6NDD

Are you sure it's a linear?
It might be a class C, FM only, amp.
What is the make, and model?

If it is a linear it's much better to hard switch it.

Cheers

Tony

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Wed May 10, 2017 8:28 am
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 Modding a linear the work on SSB (Help Needed) 
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Post Re: Modding a linear the work on SSB (Help Needed)
Hi Tony,

Its an Ex-Emergency services linear that has been re-tuned to work on the 2m band, I will upload a photo of the circuit board / internals.

Thanks,

Nick


Wed May 10, 2017 8:33 am
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 Modding a linear the work on SSB (Help Needed) 
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Post Re: Modding a linear the work on SSB (Help Needed)
https://drive.google.com/open?id=0B4T6C ... Xpfak9mY1E

This is a photo of the internals,

Thanks again,

Nick


Wed May 10, 2017 8:41 am
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 Modding a linear the work on SSB (Help Needed) 
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Post Re: Modding a linear the work on SSB (Help Needed)
Does it satisfy IR 2028?

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Wed May 10, 2017 8:42 am
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 Modding a linear the work on SSB (Help Needed) 
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Post Re: Modding a linear the work on SSB (Help Needed)
I'm guessing as its ex-emergency services its going to certainly meet IR 2028 Requirements, I can have a Baofeng sitting next to it with the squelch turned off on different frequencies and no interference is picked up.

Thanks,

Nick


Wed May 10, 2017 8:45 am
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 Modding a linear the work on SSB (Help Needed) 
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Post Re: Modding a linear the work on SSB (Help Needed)
It doesn't look as if it is biased for linear operation.

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Wed May 10, 2017 8:57 am
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 Modding a linear the work on SSB (Help Needed) 
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Post Re: Modding a linear the work on SSB (Help Needed)
You will need a bias circuit, basically a variable voltage regulator to bias the transistor for linear operation.
There are numerous designs on the web, look at this one for a 70MHz homebrew linear -
Image
D1 and D2 should be physically located on the RF power device with a dab of thermal paste between the device and diode body and you will need to sink the TIP31 transistor too as it gets warm.
You will need to be able to connect an DVM to L3 and set the trimmer to a around 0.6-0.7V and check the idle current is around 50-70mA by placing the DVM in current mode between the power supply and the +V input to your amplifier.

Also, you should make provision to key the amplifier from the PTT output on your radio, otherwise you will have to modify the RF sense circuit to give an increased time constant for SSB use to avoid the relays chattering.
That design was taken from the 4 Metres website and is a proven, working design which I have used.


Wed May 10, 2017 9:08 am
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 Modding a linear the work on SSB (Help Needed) 
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Post Re: Modding a linear the work on SSB (Help Needed)
I think something has been missed or needs to be mentioned should I say.

The amplifier works on FM and AM currently, when I switch to SSB I can hear the amp clicking on and off as it uses the carrier to sense when it needs to turn on, but obviously as the carrier on SSB is intermittent it causes problems for the amplifier.

By adding a switch and a capacitor to the amplifier, the capacitor 'smooths' the carrier signal. This means the SSB signal appears to the amplifier as FM or AM and therefore the amplifier remains switched on while TXing on SSB.
The amplifier 'works' on SSB meaning it does amplify my signal but when people hear me it is intermittent as the amp is switching on and off.
I hope this makes sense... I completely understand the theory behind using a capacitor to smooth the carrier signal, I was just asking where said capacitor needs to be placed to function as a smoothing device.

Thanks very much,

Nick


Wed May 10, 2017 10:46 am
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 Modding a linear the work on SSB (Help Needed) 
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Post Re: Modding a linear the work on SSB (Help Needed)
M6NDD wrote:
I think something has been missed or needs to be mentioned should I say.



Yes, I'd say something has definitely been missed :)

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Wed May 10, 2017 11:03 am
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 Modding a linear the work on SSB (Help Needed) 
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Post Re: Modding a linear the work on SSB (Help Needed)
It's not your fault, and I hope that nobody ridicules you.

But you just need to learn a bit more about what SSB actually is before you go modding.

For example, there is no actual 'carrier' on SSB .. it's all just 'voice' and you need a different 'class' or 'configuration' of amplifier to transmit it.

You just haven't been taught that yet.

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Wed May 10, 2017 11:07 am
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 Modding a linear the work on SSB (Help Needed) 
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Post Re: Modding a linear the work on SSB (Help Needed)
Basically; not every RF amplifier is a linear. Only a linear is a linear.
If it's come from out of a van / fire engine etc. or base station, it's unlikely to be a linear, and will only work for FM and AM.

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Wed May 10, 2017 11:37 am
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 Modding a linear the work on SSB (Help Needed) 
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Post Re: Modding a linear the work on SSB (Help Needed)
G6CSL wrote:
Basically; not every RF amplifier is a linear. Only a linear is a linear.
If it's come from out of a van / fire engine etc. or base station, it's unlikely to be a linear, and will only work for FM and AM.



And not properly on AM :)

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Wed May 10, 2017 11:38 am
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 Modding a linear the work on SSB (Help Needed) 
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Post Re: Modding a linear the work on SSB (Help Needed)
Well fair enough, like you say I need to read up on SSB and types of amplifiers, I haven't been taught that yet, so thanks for the advice guys, I will go and read up on amplifiers and SSB, after all I'm only an M6 and you were all foundation licence holders at some point, if people feel the need to ridicule me I think they should think back to when they didn't know what they know now and the mistakes they made back then.

Thanks again!

Nick


Wed May 10, 2017 11:42 am
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 Modding a linear the work on SSB (Help Needed) 
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Post Re: Modding a linear the work on SSB (Help Needed)
M6NDD wrote:
Well fair enough, like you say I need to read up on SSB and types of amplifiers, I haven't been taught that yet, so thanks for the advice guys, I will go and read up on amplifiers and SSB, after all I'm only an M6 and you were all foundation licence holders at some point, if people feel the need to ridicule me I think they should think back to when they didn't know what they know now and the mistakes they made back then.

Thanks again!

Nick


I don't think that anybody wanted to ridicule you. We all started somewhere, and I asked questions far more stupid than you can even imagine.

Maybe they were thinking the same as me: ''How do I tell him without sounding as though I am ridiculing him''.

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Wed May 10, 2017 11:53 am
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