bad swr reading

[dudmuck]

Resonance deals with there not being any reactance present in the input impedance, only resistance.

I guess thats correct, but I wouldn't quite say it in that way. I would say: resonance is where capacitive and inductive reactance are equal. And of course they don't necessarily have to be equal at 50ohms, could be whatever you want it to be.

The problem is that reactance doesn't radiate, only the resistance does.

Hmm. I ponder on that one. Another way of thinking is a dummy load is purely resistive. Stick a 50ohm resistor in the back of your CB and transmit. Very little power will be radiated, mostly heating the resistor. Purely resistive, only the stray capacitance and inductance of the resistors leads will cause radiation. So in that way, you could say only the reactance radiates.

I'll just say if something has reactance, its either capacitive or inductive. And if you put a piece of coax between you and that reactance, it will phase shift and eventually become the opposite, ie if it was inductive it would become capacitive ran though a 1/4 wave length of coax.

sorry for hijacking the thread.

 

[Beetle]

[quote="dudmuck
>>I guess thats correct, but I wouldn't quite say it in that way. I would say: resonance is where capacitive and inductive reactance are equal. And of course they don't necessarily have to be equal at 50ohms, could be whatever you want it to be.

Beetle writes:
You have to look at the entire puzzle, not just one piece. At resonance, the reactive vectors are equal and opposite, and therefore cancel each other. Therefore there truly IS NO reactance.


>>Hmm. I ponder on that one. Another way of thinking is a dummy load is purely resistive. Stick a 50ohm resistor in the back of your CB and transmit. Very little power will be radiated, mostly heating the resistor. Purely resistive, only the stray capacitance and inductance of the resistors leads will cause radiation. So in that way, you could say only the reactance radiates.

Beetle writes:
In order to radiate RF, power has to be dissipated. Reactance does NOT dissipate any power, by definition. In the case of the 50 ohm resistor (and let's specify that it's a non-inductive resistor), it IS radiating. Not very efficiently, however, unless the physical size of the resistor is somewhere around a half wavelength at the frequency we're using.

In an antenna, it's the "radiation resistance" that dissipates the power. If the antenna is well designed, it dissipates the power so efficiently that it barely gets warm - if at all. The resistor (or dummy load) is grossly INefficient as an antenna. That's why it gets hot.


>>I'll just say if something has reactance, its either capacitive or inductive. And if you put a piece of coax between you and that reactance, it will phase shift and eventually become the opposite, ie if it was inductive it would become capacitive ran though a 1/4 wave length of coax.

Beetle writes:
Check a good antenna book under "transmission lines".

>>sorry for hijacking the thread.[/quote]

 

[dway87]

i got the swr below 2 across the board. now i am not getting any feedback when the squelch is set all the way to the left. also when i hit the ptt, the meter only goes to 1.5. so what's wrong now?