SWR meter readings after a mistuned amplifier. Looong.

[Marconi]

I had an idea the DB used pretty short feed lines Bob. I think that was based on his previous information. So, where are we now? I just see this idea a little differently and I wish I could explain my own ideas. I know, an idea that cannot be explained is not a real idea or a good idea.

I don't understand all the details of this discussion, and I probably should say nothing, but could theory be based strictly on a perfectly matched and balanced feed point load, and that is not so easy to achieve with CB tools? Thus, even minor errors complicate the results due to our testing tools and procedures experiencing complex matches instead of perfect matching loads.

I would think that unless we were very luck with every tool we use...we could be dealing with some compounding errors effects for correctness in each device, and thus results are just close, but not really convincing beyond all doubt in attempting to duplicate.

IMO, theory has to be based on extremely close and maybe even right dead-on perfection. So, maybe that is why real high tech testing, using very expensive, and highly technical test equipment and procedures is required for perfect results...that are truly duplicable in a real lab setting.

Maybe at best, using the tools available to us in CB, we can establish trend lines that will follow the ideas for theory, but yet and still be a little off, not allowing for perfect duplication in processes. Like I post in my signature: "...we're lucky we don't have to be perfect to work our radios..."

All I can make of this discussion is that I think to some extent...this is the point I've been trying to make in several attempts...and I still get confused.

Thank you db and the other guys for this discussion. I wish I could add something constructive however.

 

[psycho]

Reading this thread just made my head explode.



http://www.youtube.com/watch?v=HY-03vYYAjA

 

[bob85]

DB have you tested your meters with reduced power to see if they are not reading linear at low input power?.

 

[The DB]

DB have you tested your meters with reduced power to see if they are not reading linear at low input power?.

The second time I ran through the test I had consistent readings after readjusting the forward control every time I saw a change in the reflect, which suggests that the test meter was reading linear. Before I run the test again I will double check to make sure. It shouldn't be to difficult with a radio with a variable output and a set of test loads.


The DB

 

[The DB]

I redid the test this morning, there was a change or two in the setup overall but not much.

Starting out I have my RCI2950 connected to a three foot piece of RG-8X. That is connected to a tuner, which is connected to the SWR meter with another three foot piece of RG-8X. During the test I tested the load while it was both directly connected to the meter, and connected to the meter through a five foot piece of RG-8X. I also used an SO-239 connector with wires hanging off the center and outer conductor for a high reactance test.

Before the test I checked my meter with the two test loads and the test antenna, using the knob on the radio to control power output I used the power levels of 2 watts (all of the way down), 5 watts (about the middle), and 10 watts (all the way up). The meter read consistently with both test loads through the power range tested giving the expected results.

During the tests I varied the output power of the radio between 5 and 10 watts (dead key with the microphone gain and the gain knob on the microphone itself turned all of the way down). I only used the 100 and 450 ohm test loads and the quick antenna I set up for the high reactance testing for these tests.

I used a frequency that presented R of 127 and X of -110 and an SWR of near 4.5:1 as read from an analyzer plugged directly into the antenna.

The SWR, after readjusting the forward control when there was a change, always went back to where it was before I adjusted the antenna tuner. This is with both test loads and the high reactive test antenna, and using 5 and 10 watts of drive. Adding a five foot length of coax between the meter and the test loads/test antenna also had no perceptible effect.

My conclusion from this testing is that the SWR meter can only give you accurate readings of the antenna system after the meter in the system. Where the readings did initially change with a change in the system before the SWR meter, they returned to their original readings when the forward control was reset to the set point on the meter.

So while an SWR meter can signal that a change, such as tuning the output of an amplifier, or antenna tuner, or perhaps a coax went bad, has taken place before it in the system, all it can tell you is a change happened. Further, the change that an SWR meter will detect in the system is limited to the amount of power that makes it to the SWR meter to begin with. As I said above, if you re-adjust the forward control on the SWR meter, the readings go right back to what they were before the change.

So, now I have three questions...

Is there anything I can test further with this setup?

Are there any potential errors that I may have made in the testing?

Is there anything else I can do to make this testing either more accurate or, perhaps, more complete?


The DB