Predator 10k

[Lazybones1222]

Very informative post W5LZ. Thanks.

I found this at http://www.amateurlinearamplifiers.com

I found it interesting they said to make all SWR adjustments with the linear out of line, then add the linear in place of the SWR meter. Comments?

Cut and paste: found here

What SWR ratio is acceptable?

Obviously, the lower the SWR ratio the better your system will perform. Practically, it's not possible to achieve a 1:1 matching condition. As a rule, amplifiers up to the 500W range should not exceed an SWR of 1.8:1. This will ensure that heat dissipated within the amplifier caused from mismatch reflections is within tolerable limits.

What is the procedure for setting SWR?

As stated earlier, the SWR ratio is normally reduced by changing the length of the antenna radiator. Follow the steps below for proper adjustment:

IMPORTANT - MOST SWR METERS ARE NOT DESIGNED TO HANDLE HIGH POWER LEVELS,MAKE CERTAIN AMPLIFIER IS OFF FOR ALL SWR MEASUREMENTS AND ADJUSTMENTS

· Insert an SWR meter in the system as shown in figure 2.
· Key the transmitter and note the SWR ratio reading. (Refer to the SWR meter instruction manual for exact measurement procedure for your particular model meter.)
· If ratio is greater than 1.8:1 adjust the length of the antenna radiator and recheck. Repeat measurement/adjustment procedure as necessary until ratio is 1.8:1 or less.
· Remove the SWR meter from the system and reconnect antenna to amplifier output.· This concludes the adjustment procedure; the amplifier is ready for operation.

end cut and paste

 

[W5LZ]

I'll make this comment.

If the output impedance of both radio and amplifier are reasonably 'close', maybe something within about 10% of each other, then the quoted tune up/testing procedure will work just fine. That assumes that the quality of design and construction of the amplifier is adequate. That 'in line'/out of line' thingy I take to mean turning the amplifier off so that it's by-passing circuit also meets the 'quality' that should be expected.
[Actually, that procedure is fairly typical, most everyone does it that way, sort of.]
As far as removing the SWR meter and replacing it with the amplifier, well, can't say I'd do it that way. I'd leave the meter in line, for two reasons. First, it can handle the power levels I'm likely to use. And second, how would I know if things stayed the same if I couldn't measure it? (And third, considering the above two thingys, I'm too lazy to take it out of line.)

Gotta be a 'catch' somewhere, doesn't there? I'm sorry to say it, but yes, there is. All of the above is based on some assumptions about equipment that is not held to any quantified standards. No matter what you call them, the amplifiers shown in that site are not "amateur" or "ham" amplifiers, which are held to quantified standards. They have not been submitted for FCC testing and acceptance. So, no matter who made them, they are one of them "take it as it is" thingys. Solid state devices are just not as 'tolerant' as tube devices unless they've been sort of "over-built" with safety circuits. Not that there's anything wrong with solid state amplifiers, there isn't, they certainly do have their places. Depending on what they are compared to, they tend to be a bit more 'delicate' than tubes...sort of.
Enough of all that...
- 'Doc

 

[Lazybones1222]

I agree. I found this paragraph to be the most interesting:

"IMPORTANT - MOST SWR METERS ARE NOT DESIGNED TO HANDLE HIGH POWER LEVELS,MAKE CERTAIN AMPLIFIER IS OFF FOR ALL SWR MEASUREMENTS AND ADJUSTMENTS."

CB SWR bridges are really for a 4 watt dead key, so it may be true of the cheaper meters. Like Beetle taught me long ago, "SWR is a ratio and does not change with the addition of power." It is what it is.

So I think often it is false readings on cheap meters that hose things up on the quest for a great match at high wattage settings. Your thoughts?

BTW - Justin Depolis tuned the input and output of my amp (after it blew up - lol). It is spot on now. When it blew up, the manufacturer said I blew it up via operator error. Funny thing is, I have run that amp for over a year now after Justin went through it, running it the same way as before, and it operates flawlessly, unless you volt it in AB class bias (the amp has switchable bias).

Lazy

 

[W5LZ]

Beetle is correct about SWR being a ratio and so doesn't change with power levels. He/you are also correct about all meters not being equal for various reasons. Another way of saying that is that all meters are not as accurate as others, depending on the power range they were 'optimized' for.
All analogue meters have varying accuracy over parts of their scales, low, medium, higher range, and that accuracy varies in how much each meter can be inaccurate. A very rough estimate is something like 10% (yeah, even them Birds). If you aren't doing something that requires extreme accuracy, that 10% won't make a hill of beans worth of difference in the actual readings.
[If I'm not mistaken, Bird optimizes for mid-range with most of their 'slugs', which makes sense when you think about it.]
Digital meters, because of their design, -can- be more accurate in general. That doesn't mean that they are, just that they can be. I'm not hugely enthused about digital meters. For me, they are a bit harder to read "trends", usually much easier to see with a mechanical meter movement. That "swang" thing, how fast/how far etc. Whoo-pee, big deal, right?
Handling higher power just depends on what the meter was made to handle. Some can, some can't. Just looking at most meter's scales should give you an approximate clue to their abilities, and tell you if they can be used at whatever power level you happen to want to measure at. And as with all things like that, having a greater ability than actually required is a very nice 'fudge-factor'/safety factor.
I like 'dual' type meters. They can give you readings of multiple things at one time. They also have disadvantages, mainly price (there are two meters in that one box so twice as much isn't all that unreasonable, right?). Are they the 'best'? Not really, but they are more 'comfortable' for me, I certainly don't need 'lab' accuracy, and I don't have to wonder which one'a them @#$ things am I supposed to be reading!
"el-Cheapo" meters are just that. Doesn't necessarily depend on price. Using anything for something it wasn't designed for isn't exactly the smartest thing in the world. So that statement about 'cheap meters' and high power is certainly always true to some extent. Knowing when you reach that 'extent' is the biggy. So starting 'small' and working up to 'big' is a smart thing to do.
- 'Doc


(It's also nice to have one'a them el'cheapo thingys laying around so you have something to blame when you goof. ... not that I'd ever do such a thing!)

 

[mackmobile43]

roger on the volts.....I have also learned the hard way if the amp is ab bias.....no volting allowed

Yes the regulator circuit for the biasing couldn't handle the over volting.

 

[mackmobile43]

I agree. I found this paragraph to be the most interesting:

"IMPORTANT - MOST SWR METERS ARE NOT DESIGNED TO HANDLE HIGH POWER LEVELS,MAKE CERTAIN AMPLIFIER IS OFF FOR ALL SWR MEASUREMENTS AND ADJUSTMENTS."

CB SWR bridges are really for a 4 watt dead key, so it may be true of the cheaper meters. Like Beetle taught me long ago, "SWR is a ratio and does not change with the addition of power." It is what it is.

So I think often it is false readings on cheap meters that hose things up on the quest for a great match at high wattage settings. Your thoughts?

BTW - Justin Depolis tuned the input and output of my amp (after it blew up - lol). It is spot on now. When it blew up, the manufacturer said I blew it up via operator error. Funny thing is, I have run that amp for over a year now after Justin went through it, running it the same way as before, and it operates flawlessly, unless you volt it in AB class bias (the amp has switchable bias).

Lazy

NOTE: SEE PREVIOUS POST