| Author |
Message |
    
Radio_terminator
New member
Username: Radio_terminator
Post Number: 8
Registered: 2-2006
| | Posted on Saturday, June 03, 2006 - 4:07 am: | 
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Hello...
Could a knowledgable tech please explain how to properly tune the input swr, and/or the output swr on a solid state amplifier?
I have a couple of Cobra XL-450's I would like to custom match to my base and mobile installations.
I really apreciate any light you can shed on the subject. I'm sure there are others who would appreciate this information as well.
Thank you.
RT |
Georgeodjungle
Intermediate Member
Username: Georgeodjungle
Post Number: 109
Registered: 1-2006
| | Posted on Saturday, June 03, 2006 - 12:59 pm: |
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for input on tx would be the resistor(s) by the lil transformer.
should be around 50 ohms.
for output on tx is the last cap between the big transformer & ant out.
could replace with a trimmer.
also:
different lengths of coax effects rx & tx.
with out a schematic that's the best way i can explane it to ya. |
Hotwire
Senior Member
Username: Hotwire
Post Number: 1430
Registered: 1-2005
| | Posted on Saturday, June 03, 2006 - 1:36 pm: |
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The only way to obtain a low swr is by tuning the antenna. On a tuneable antenna you just move the whip or stinger in or out of the load which is adjusting the length to get it electrically correct to the frequency that your wanting to use. Pretuned antennas like the Francis whips are set from the factory so as long as you install it right by the instructions on the package you are good to go. the 102 inch stainless steel whip and the 96 inch fiberglass whips are also the perfect size, no need for tuning them either. Just mount a 102 inch whip to your vehicle with as much whip above the vehicle as possible and be sure the mount is grounded well.
There is absolutley no other way to adjust SWR. As long as the cb sees a 50 ohm antenna provided you have 50 ohm coax your ready to talk! good luck |
Radio_terminator
New member
Username: Radio_terminator
Post Number: 9
Registered: 2-2006
| | Posted on Saturday, June 03, 2006 - 5:41 pm: |
|
Yes, but sometimes an amp designed to operate on 10 meters must be retuned to be as perfectly matched as possible with an 11 meter radio and antenna. With tube amps, it is done by adjusting the tuning slugs ect...
Can a TECH please explain how this is done on my solid state amps? I'm only interested in hearing from a pro. I'm sure there must be a tech on this board who knows how this is done.
Thanks... |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 2927
Registered: 7-2004
| | Posted on Saturday, June 03, 2006 - 7:03 pm: |
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most solid state CB-type amps are more then broad-banded enough to operate perfectly well on 12, 11 or 10 meters, if not even wider. ham-type solid state amps are built to block out freqs above 21 mHz. a change to the matching transformer's windings & diode or 2 solves that problem.
but that's not what you're really asking. they don't need to be tuned like a tube amp. if built 'right', they are 'there' already. some use trimmer caps for fine tuning, other builders are confident they got it right with a fixed value cap. and even others hope their matching coils are close enough.
what amp in particular are you talking about? |
Radio_terminator
Junior Member
Username: Radio_terminator
Post Number: 10
Registered: 2-2006
| | Posted on Sunday, June 04, 2006 - 4:56 pm: |
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A Cobra XL-450. It's an exact copy of the original Magnum amplifiers. I'd like to know the procedure for fine tuning the input/outputs. I believe that it is probably adjustable. There are two variable pots (or caps) with screwdriver slots in them.
But, I'd like to know EXACTLY how to do this, because I definitely do not want to screw anything up (no pun intended).
I want it to be as perfectly matched with my radio and antenna as possible. |
Radio_terminator
Junior Member
Username: Radio_terminator
Post Number: 11
Registered: 2-2006
| | Posted on Tuesday, June 06, 2006 - 5:58 am: |
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Gee...
I thought that this section of the forum was called "ask the tech".
Are there any techs here at all? |
Tech808
Moderator
Username: Tech808
Post Number: 10198
Registered: 8-2002
| | Posted on Tuesday, June 06, 2006 - 8:01 am: |
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Radio_terminator,
As posted by other's above you adjust your SWR by adjusting your Antenna to the Lowest SWR reading you can get NOT the Radio or Amplifier.
Antennas are very dumb and do not know if you just have a radio in line or a radio, meter and amp in line.
Step #1 ~ Connect your radio via a coax jumper to the INPUT side of a Good / Accurate SWR Meter and then connect your Coax from your antenna that you have tested and know it is good to the OUTPUT side of the meter.
Step #2 ~ Adjust your antenna to achieve the LOWEST SWR you can get.
Step #3 ~ Then when you have an swr of around a 1:1 you can add the amplifier in line and check the SWR again.
Step #4 ~ Your SWR should be around a 1:1 to 1:5 depending on jumper length which you may have to try different length's.
This has been covered many times before here in the Copper Forum.
As for the Input from your radio to your amplifier your owner's manual/operating instruction's should tell you the minimum and maximum input power from the radio required for maximum performance.
As for the Output of your amplifier it will depend on if your radio is set up properly to achieve 100% maximum performance and set to the the specifications of the amplifier for INPUT.
NOTE! If you are using a Cobra XL-450 and it has been converted to operate on 11 meter's your will NOT have to adjust anything inside of it.
And if you follow the GOOD advice above your post from the other member's who have posted with helpful advice and many year's of 1st hand experience and 10's of thousand's of hours of using amp's you should have no problem's and there is not much more advice a Tech can add.
You may also want to go to the area below and read the Topic titled Mobile Amplifier Installation Tips:
Subscriber (Preview)
» Articles
» Mobile Amplifier Installation Tips
or just CLICK HERE!
And if you are using a mobile amp inside running it off a Power Supply you will need a Power Supply that is rated with enough power to handle BOTH the Radio and the Amplifier to reach maximum performance.
Hope this help's,
Lon
Tech808
CEF808
N9CEF
CVC#2 |
