Kl 203p HIGH swr

Hello!

I have bought a secondhand kl 203p amp but when i tried it out the swr went trough the roof. Like 7-8 in swr.. Worth mentioning is that this is my very first amp ive own so i dont know if im doing something wrong but I think i have done everything right. Wonder if i might have bought a damaged amp maybe... I have tried with the amp turned off also but the swr is the same

How have you got in situe , it should be Radio patch lead in to transceiver side of amp the another patch lead from Antenna side of Amp in to transceiver side of Swr/Pwr meter then antenna in antenna side of meter ,also every time you use the amp you must check the SWR by how you've always check it ,plus before you use a amp make sure your SWR is below 1.5 anyway, also those amps can only accept 5 to 10 watts on AM/FM, and up to 20watts SSB  if you put more than that in to amp you will overdrive it and stand a good chance of blowing the output transistors.

Yeah, i have done everything just like you should do with the swr meter but even then its sky high... The thing im wondering is if i might have a too short jumper between the amp and radio? Its only about 50 cm. But could that be the reason why i have so high swr? 8 in swr is pretty high.. Is there any way to measure if something is burnt in the amp?

The only way is to open up the amp to see if you can see anything burnt sometimes you can actually smell it you know like an electrical burn smell ,its unusual because these amps are pretty sturdy little amps TBH ,other that  maybe just go back and re- check everything ie: patch leads and solders  joins ,its going to be something silly and simple causing it I bet, well I hope it is keeps us informed.

Just remember coax from aerial into swr meter  swr meter to amp ANT  and amp to rig.
Test with the amp turned off.

Now opened it up and could not see any burn marks or smell of burnt. The swr is still about 8-9.. Should it be any connectivity in the center of the so239 plugs on the amp?

Sorry my friend could you explain what you mean by that , if you mean should PL259 be soldered in the centre of the plug where the twisted copper of the coax goes through then yes if different can you explain please mate

Yeah sorry for my bad english haha.. The center pin on the so239 connections on the amp. Should they be connected to each other. I mean if I take the multimeter and put on both center pins on the back of the amp they are not connected to each other. Hope you understand this time. Need to take a better multimeter and try to measure the diodes if I can find any fault.

You won't get a connection on each centre pin as it's got a circuit in-between.
Without the amp inline is your SWR ok.

Okay, i suspected something like that. No the swr is the same all the time whatever i do... Its like clicking each time i ptt. Guess its only the relay doing its thing.

Is the SWR ok without the amp inline.

Inline, Is that with the amp off? If so, no its the same with it off or on. I cant really understand whats wrong....

With the amp unplugged out of the room even.
Just the aerial into the SWR meter and patch lead into the radio.
Then check the SWR.

Ah okay. Yeah then its about 1.1 without the amp.

Right
But when the amp is inline switched on or off your SWR is sky high.
Is that correct ??

LOL my Swedish isn't that good either in fact none existent,  Alan has asked the questions I was going to ask next so let's us know, but the way you describe your problem it maybe something to do with when the amp is in line .

That was my next,,,,,,,,,,,Faulty amp.
Sorry didn't notice the location.

The question's already been asked but the commonest SWR problems I've seen is placement of the SWR meter.


21ASN93, are you connected like this? :-

RIG <-----> KL203 Linear <-----> SWR Meter <-----> ANTENNA


Some will argue about this but I've never seen the point of measuring the 'linear' SWR(?) only the power input to it.

Also remember "Crap In = Crap Out"

If you have a rig kicking out spurious harmonics, (54-56Mhz is not unusual), the linear is so wide-banded it will amplify the harmonics as well!! The typical CB SWR meter is also wide-banded, (3-200Mhz in some cases), and can't differentiate the harmonic crap coming back. Obviously your antenna is tuned to ~27Mhz and all that amplified harmonic content will come crashing back down showing you a high SWR.


How do you fix it?

A typical TVI filter will cut down the amount of harmonic crap your rig is kicking out before you start amplifying it. (Should've been done in the radio but low pricing/cheap manufacturing ie Chinese means it usually isn't!)

So :-

RIG <-----> TVI Filter <-----> LINEAR <-----> SWR Meter <-----> ANTENNA


That usually fixes common 'linear' SWR problems right off the bat.


Some manufacturers tell you to cut a certain length of coax for the rig to linear connection, it's usually a vain attempt at impedance matching and hopefully reducing your harmonic content along the way. The 'TVI Filter' will usually fix your impedance as well as reduce harmonics and provide a much needed fix for poorly designed MOSFET to MOSFET connectivity.

(We didn't get these issues with the old transistor & valve stuff did we fellow 'old gits' )


Often operators ignore all the above as the rig & linears don't 'blow up' and merrily transmit harmonics all over the place.........

Anyway, hope that helps the OP, anyone else reading this or even if anyone bothers to search the forum in future


All the best,
Victor

Victor wrote:

Some will argue about this but I've never seen the point of measuring the 'linear' SWR(?) only the power input to it.

You should do because there's impedance matching on the input and with valve linear amps you can tune that too.

If there's a fault on the input side you'd not know if you didn't check it.

What is the SWR when you put the meter between the output of the amp and the antenna? If that is also high then it suggests a RF ground issue. If it isn't then it supports the amp being faulty.

Just a thought but is the amp definitely for 27MHz and not for UHF 144MHz.

Alan Pilot wrote:

Just a thought but is the amp definitely for 27MHz and not for UHF 144MHz.

KL203 amps are for CB use  one of the most popular amps about because they're sturdy little amps 200watts SSB 100w AM/FM they go from 20mhz to 30mhz 
unless someone has been inside and messed about with it to change the frequency workings

OOPS i forgot the KL-203 bit at the top.
Sounds like it's goosed then to me.

The circuit in these type of linears are actually just a wide-band RF amplifier. 

Many a knowledgeable Ham or electronics enthusiast know that they can easily operate from 1.8MHz to 30MHz as they aren't tuned to anything, the limiting factor being the MOSFET switching speed. Nowadays the Chinese are slinging more than IRF510's in them and using any MOSFET available to hand, some of them capable of switching up to 150MHz. As there is no output filtering in these type of units they will amplify everything including the spurious harmonics! 

On most CB's the output 'filtering' is performed at minimum cost to achieve FCC or CE approval. In other words they don't eradicate it completely, just do enough to pass. All of that fine until you 'amplify' those small spurious harmonics to make dirty great big ones.

Various legislations start to make sense......

These amps are made in Italy Victor there not Chinese crap , there Italian crap LOL as some say , no joking apart the Italian made amps ie: Zetagi ,RM,  are not too bad for what they are and what they are used for I will admit they do over exaggerate about there power output a bit  but also do some of the Chinese companies about how good and reliable there CB transceiver are .

I learn something every day.
Thanks Victor.