swr goes up when amp is used

[airplane1]

Thanks for all the info posted for me. I was looking in the very poor manual for my AL-811 and nothing exists on tuning the inductors so I will call Ameritron and ask if they can tell me the correct method. I only use it on 10 right now not 12 at this time till I get my general.

I was checking the setup at the coax comming in the shack to back of amp with my mfj259 and it is showing me 1.2 on 28.360 with Z= 50 and. Now when I hook the the mfj259 to the coax comming out of the amp that connects to my radio I see 1.3-1.4 and a Z= 40 and no matter what freq I set the mfj it will not go to Z=50 so would that back up what you all are saying about needing to tune the amp with the inductors in the back?

Now I want to say also that the swr goes up as power goes up, at very low power it is within goos swr readings. just want to give as much info as possible to get best help.

Thanks,
AP

 

[Slam Dunk]

wow, this tuning sounds complicated. the link you supplied is a wealth of info but a bit over my head.

Find yourself a Workman PDC 5 SWR Meter and Matcher, put it in between your radio and the amplifier and use it to adjust the "SWR" (input tuning) into the amp. Turn the Matcher off when not using the amp.

This is an external solution that is easily applied by appliance operators asking disingenuous questions. This works especially well on Chicken Band amplifiers constructed without input tuning when used with radios without built-in SWR bridges.

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ETA: Only Generals and above are allowed to operate more than 200 watts on 10 meters, "n'est pas"?

.

 

[ButtFuzz]

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ETA: Only Generals and above are allowed to operate more than 200 watts on 10 meters, "n'est pas"?

.

Oui, c'est vrai!

Technoids are allowed 200 watts max AND only phone privs are betwixt 28.3 and 28.5. AND that is only SSB. No AM or FM... I was taking my General exam this week-end, but I'm headed for the beach. I've already called the beach ARC, and they're not testing until July sometime. So.... Hopefully next weekend I'll upgrade to Extree Class...

'Fuzz

 

[airplane1]

I know only 200 watts as a tech, that is what I run if needed and it made a difference several times to get a contact I could not with out it. I mostly use just the radio and have amp on standby and tuned and setup on 28.360USB 200 watts so if an op can not quite hear me I flip the swich.



I will be able to use it full power if needed when I get my general.

 

[BOOTY MONSTER]

WOW !!!!
FINALLY.....a post about correcting this problem instead of just using different coax jumper lengths to fool a meter into thinking a problem is fixed .

 

[Moleculo]

I was checking the setup at the coax comming in the shack to back of amp with my mfj259 and it is showing me 1.2 on 28.360 with Z= 50 and. Now when I hook the the mfj259 to the coax comming out of the amp that connects to my radio I see 1.3-1.4 and a Z= 40 and no matter what freq I set the mfj it will not go to Z=50 so would that back up what you all are saying about needing to tune the amp with the inductors in the back?

AP

Remember, your rig doesn't see the antenna when the amp is turned on. The only load it sees is the amp. You can tune the input swr of the amp using your MFJ-259. Just use the same jumper that you would use for the radio, but put the analyzer on the frequency you want to adjust the amp's input swr for. Now just take your slug tuning tool and turn the slug labeled AUX very slowly while watching the Analyzer. When you get it where you want, you're all set. You may not be able to get a perfect 1:1 match, so don't stress over it.

Here's a pic of the back of the amp, for everyone else following along:

 

[airplane1]

Very Good moleculo, Thanks, I will be at rad shack after work today and hope they got the plastic tune tool. If not I will order one from Ameritron. I bought the AL-811 used but it is only 3 or 4 months old and mint condition but don`t know, He maybe or mabe not messed with the Aux slug as it was converted to 10 meters when I recieved it.

Question again Moleculo, will the slug tuning change just the swr or will it bring the Z= to 50 ohm`s too?

I will tell ya, the manual leaves alot to be desiered. Newbies like me need better instructions Ha Ha. I like this amp very much, it is farely quiet and easy to tune.

I will let you know how it goes,
AP

 

[W5LZ]

It depends a lot on exactly what you mean by that 'Z'. There are quite a few 'Z's that can be 50 ohms impedance and not 'R'=50 and 'X'=0, or resonant. If you can't get the ideal, then as close as possible is the next best that you can hope for, and is typically 'good enough'. Just means you won't be driving that amplifier with every single watt out of the radio, which isn't exactly the worst thing that can happen.
Opening up 10 meters on most of Ameritron's amplifiers is one of those "clip the green wire" thingys. If the band switch has been modified much at all, then all bets are off, no idea what ~could~ have been changed. Running down circuits is SO much fun!
- 'Doc

 

[airplane1]

My mfj 259 has a swr display and an ohm disply that shows it as Z= whatever it is. I take it it is the coax ohms not. or would the coax not change when frequency changes.

I wish someone could teach me how to use the mfj 259. it does not have the x= on it ,just swr and z= ohm.

 

[C2]

You can tune the input swr of the amp using your MFJ-259. Just use the same jumper that you would use for the radio, but put the analyzer on the frequency you want to adjust the amp's input swr for. Now just take your slug tuning tool and turn the slug labeled AUX very slowly while watching the Analyzer. When you get it where you want, you're all set. You may not be able to get a perfect 1:1 match, so don't stress over it.

Would he need to manually key the amp during this procedure?

Otherwise, he would be looking at the thru path for receive and actually see *some* of the antenna's affect...

 

[Moleculo]

Yeah manually key it, or use the rig in SSB mode with the mic disconnected (so you don't modulate accidenally) if you have no antenna attached to the rig.

 

[airplane1]

I am confused now! sorry, I need to key the amp to see the high swr jump that is not there without power. so then the mfj will show the high swr and I can adjust the slug? If the rig is in ssb and mic disconnected then the rig cant key and excite the amp.

 

[airplane1]

how do I manually key this amp?

 

[C2]

Yeah manually key it, or use the rig in SSB mode with the mic disconnected (so you don't modulate accidenally) if you have no antenna attached to the rig.

I'm thinking you do not want an antenna connected to the amp

BUT you DO want a dummy load connected to the output.

The analyzer might drive it somewhat...

We are adjusting the input impedance to the amp, right?

 

[Moleculo]

Yeah, we're adjusting input impedance. Sorry Airplane, I think I confused things to much by trying to describe how you could do this with the analyzer. To keep it simple, just use the swr meter on the rig and adjust the tuning slug until the rig is happy.