adding coax lowers SWR reading on the meter?

[mr_fx]

this goes against everything I have ever believed

well I added some coax between the meter and the antenna

tried a few different lengths, each time causing a different SWR reading on the meter... how is this possible?

BTW the longer one (about 2-3 foot) gave the lowest SWR reading

 

[mackmobile43]

check for lack of counterpoise.

 

[W5LZ]

It's possible, and absolutely normal, because the load at the end of that feed line isn't the same impedance as that of the feed line used.
Change that "feed line" to "transmission line" and it holds true for anything/everything fed an alternating current. That means antennas, or amplifiers, or power lines, or audio devices, whatever.
- 'Doc

 

[RatsoW8]

It's possible, and absolutely normal, because the load at the end of that feed line isn't the same impedance as that of the feed line used.
Change that "feed line" to "transmission line" and it holds true for anything/everything fed an alternating current. That means antennas, or amplifiers, or power lines, or audio devices, whatever.
- 'Doc

If your antenna is not tuned properly then adding or removing coax to match it is essentially causing the feed line to become part of the radiator. This isn't what youi want to happen. You want the power to be radiated by the antenna and NOT the coax.

 

[mr_fx]

I guess I forgot to mention... it is an Antron 99

 

[W5LZ]

What antenna it is really makes no difference. With that particular one you at least have a convenient way of changing it's input impedance. That set of rings do come in handy.
- 'Doc

 

[mr_fx]

so is it time to build an 'ugly balun'?

 

[mr_fx]

ALSO I tested it with an 18 foot section of coax (RG58u) and got flat SWRs all across the band

 

[mackmobile43]

this goes against everything I have ever believed

well I added some coax between the meter and the antenna

tried a few different lengths, each time causing a different SWR reading on the meter... how is this possible?

BTW the longer one (about 2-3 foot) gave the lowest SWR reading

I would tend to think that your antenna is not resonant at the frequency being used at, plot your swr range if you have free band capability to see where your bandwidth is then try to center your antenna to accommodate the radio.

 

[Marconi]

ALSO I tested it with an 18 foot section of coax (RG58u) and got flat SWRs all across the band

Really! I would think the very opposite might happen with a short coax vs. a long coax. Plus an A99 typically has a very wide bandwidth of 3-4 mhz without radials if mounted in the clear and a wavelength high or more. With radials, the bandwidth is reduced somewhat and the curve is more pronounced. My A99 always shows a nearly flat SWR curve accross the CB bandwidth...whatever the SWR is.

 

[mackmobile43]

Really! I would think the very opposite might happen with a short coax vs. a long coax. Plus an A99 typically has a very wide bandwidth of 3-4 mhz without radials if mounted in the clear and a wavelength high or more. With radials, the bandwidth is reduced somewhat and the curve is more pronounced. My A99 always shows a nearly flat SWR curve accross the CB bandwidth...whatever the SWR is.

Sounds like it has very good heat absorbing properties or does it just transfer that heat onto the coax.

 

[mr_fx]

well the 4.25" 5 turn choke did the trick... max SWR is now 1.25 in the CB band and it stays under 1.7 a band up and a band down

 

[mackmobile43]

well the 4.25" 5 turn choke did the trick... max SWR is now 1.25 in the CB band and it stays under 1.7 a band up and a band down

This generally helps with the absence of sufficient counterpoise.

 

[Beetle]

Use about 500 feet of RG-58. You'll have nice, low SWR even with no antenna connected!

 

[mackmobile43]

Use about 500 feet of RG-58. You'll have nice, low SWR even with no antenna connected!

Should we tie a knot in the radiating end or leave it open?