There seems to be a lot of mis information out there on antennas and transmission lines.

 There seems to be a lot of mis information out there on antennas and transmission lines. I will from time to time add a short post of fact that I thing is good to know. Hopefully they can be of use to the average amateur radio operator on anyone who want to learn about antennas and how they work.

Mostly we will consider wire antennas and coax transmission lines. There will most likely exceptions to every rule. I will try and avoid the use of always in most cases. If I do use "always" please remember there is almost "always" going to be an exception!

SWR is only an indicator of how well the antenna impedance is matched to the feline or coax.

SWR is not an indicator that the antenna is radiating any kind of signal.

Low SWR can also mean excessive feed line loss and not a real good impedance match

For any new antenna and known good feed line you should pay attention to the SWR at the ends of the band or where the SWR is 2:1 and be aware of any changes that could indicate a problem. 

Remember there is truth in the old saying is "If it's too good to be true it probably isn't true" 

For example my SWR was once 2:1 at 3.7 and 3.9 MHZ and minimum at 3.8 MHz  I think the minimum was 1.5:1. The antenna worked great. One day I noticed my 2:1 bandwidth was almost 3.5 to 4 MHZ.  The minimum SWR was also almost 1:1.  That sounds great! or does it?  I knew something was wrong. The antenna also had not been working quite as good lately either. Experience indicated that this kind of thing happens with bad coax. I had a couple connections in my RG-8U coax feeding my 80 meter half square and one 50 foot piece had developed excessive loss causing the amount of reflected power at the transmitter meter to be really attenuated reducing the SWR indication.  Replacing that 50 foot of cable brought the SWR back up to 2:1 at 3.7 and 3.9 MHz and all was well again. 

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