Home |
Search |
Today's Posts |
|
#1
|
|||
|
|||
ATU: Correct way to specify impedance range
On May 21, 11:43*am, Jeff Liebermann wrote:
On Thu, 21 May 2009 07:28:25 -0700 (PDT), ve2pid wrote: Hi to all, Just got my new ATU. The specs mentionned: Tunes 6 to 600 ohms (about 10:1 SWR range). 16 to 150 on 6M (about 3:1) It sems that this is the standardized (?) way to mention specifications... But, since impedances have both a resistive and reactive compoment, doses it means 6 to 600 Ohms "resistive"? For example , if Z= 500-J800 ohm, is it 'tunable'? I have a doubt because the impedance could also mean sqrt(500^2+800^2)=943,4 Ohms.. Thanks de Pierre Well, a little Googleing found the missing maker and model number. It's obviously made by LDG but which product? http://www.ldgelectronics.com The spec sheets aren't any more useful. *I'm also rather suspicious because ALL their products, regardless of size or technology, have the same specification. That's because all their tuners have the same component values (L and C) in the same basic tuner configuration (switched L). The various models just have different power ratings (and I suppose the loss is different) and different other features. It's a fairly straightforward process (albeit tedious) to map out all possible places on the smith chart that can be tuned to 50 ohms by their tuners. Somewhere around I have some plots I did with matlab for just that. Basically, you can get close by knowing the minimum and maximum L and C available. The step size (which is fairly even across the range... they have L and C in the 1,2,4,8 sequence) determines how close you can get to 50 ohms from some arbitrary load Z (assuming it's in range). The power limitations on a tuner are sort of complex (which is why you don't see a lot of detail). There's the current through the L and C, and the voltage on the C. There's no simple relationship between, say, vswr and component voltage/current, since it depends on the particular match configuration. What you can assume is that the potential rise is proportional to the Q of the antenna and tuner together. Since antenna Q is usually fairly low compared to tuner components, you could probably get close by taking the ratio of the antenna's reactive component to the resistive component. (short verticals, notorious for high voltages in a tuning network, have high reactance and small resistance..) |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
How much can the impedance of coax vary from its characteristic impedance? | Antenna | |||
Schedules that are correct? | Shortwave | |||
IC-781 group - correct URL | Equipment | |||
Correct Diplexer/duplexer | Antenna | |||
Is This Correct?? | Shortwave |