Problem with my portable tower

[KK4JOW]

Hi, Im hoping you may be able to help me. My portable antenna and tower are driving me crazy. I have a SuperAntenna  YP-3 "Yagi in a Bag" and one of SuperAntenna's portable 20' tower. When I install the antenna on the tower and it is lowered to about 5 ft above the ground, I can get an swr reading about 1:1. Once I start raising it the swr readings start going up. Once it is up at 20' the swr will not come down below 1:6.  This doesnt seem right to me that the swr are lower near the ground then when up in the air. Sort of opposite of what I have learned.
Has anyone ever had this happen or any suggestions on correcting this?
Thanks in advance for your help
Diane

[n1gke]

Hello from Rhode Island.
First, I had to look up the equipment and study it to know what to expect.

I see the antenna listed to cover six amateur bands. Great.

An SWR of 1:6.1 is not all that bad really.

Here are a few considerations, okay ?

1. Anything in the near field will have an effect on the radiation pattern.

2. Height above ground, or mounting surface, will have an effect on radiation pattern and
    radiation resistance, IE: reflected signal.

3. Objects in the far field will have an effect on the radiation pattern.

4. The frequency for checkng the swr have an effect on your readings as well.

5. Depending on the band or frequency you are taking the reading on, will have an effect on
    the SWR reading, and it will vary from band to band and power level to power level.

6. If your feed point or matching section is setup properly for 50 Ohm or even close to that
    and the antenna is properly constructed, an SWR of up to 2:1.0 is not all that bad really.

7. If you can check the SWR at the center of each band, out in the open away from everything
    and make a list of the readings for each band, perhaps that will help.

Time and patience can cure a lot of troubles, I don't know if this helps, but I will stick with you until
you are happy with the setup. Portable operation is great fun and most handy in times of need.

My motto ? "Find solutions, not fault."

Please, keep me posted with your progress, okay ?

73 / Myrton - N1GKE -

"I use the original form of social networking, Amateur Radio."

[KK4JOW]

Hi Myrton,
Thanks for answering my post. I have been checking everything and I managed to get the swr down to about 2:1 across the phone section of the band with the lowest being about 1:6, so I guess I am doing ok. Used the antenna during the IOTA contest this past weekend and got alot of contacts with 100 watts and this portable antenna and tower, so I really can't complain. Do you think I should just go with the antenna as it is with the above swr readings or should I hook up an antenna tuner? I already have a tuner, so I wouldn't be investing anymore. Just wonder if that would be  good way to go.
Thanks,
Diane

[n1gke]

Hello again Diane.

Just for giggles, let's be brave, courageous and bold.

Saving a long explanation, please try this.

Make the antenna with only the driven element.

Pick the band you want to operate on and set the antenna accordingly.

Check the SWR when near ground, then raise it all the way and take another reading.

Also, check the reading when half way up, all this just for the single band.

Using just the driven element you should be able to figure out where you need to set

it for best SWR for that band. Once you have something under two, then use it, just like

that, one element, rotateable dipole configuration. You will be surprised.

Now. With that under your belt and notebook pages filled out for that experiment,

try it again on the other bands and do the same thing.

Don't do it all in one day though, okay ?

Please, let me know how that works out for you. And yes, if you have a tuner built in, sure use it

if you need to, but more often than not you should not need it if the SWR is under two to one.

Just like playing an instrument and making good music, it takes a bit to learn the strings.

You will do fine now and better later. Keep up the good work and I hope we meet on the bands.

73 / Myrton - N1GKE -

[OH2FFY]

--Do you think I should just go with the antenna as it is with the above swr readings or should I hook up an antenna tuner?

Hi there

From reading your posts it is clear that your antenna had a mismatch or mistune that was giving a poor SWR reading.
This error however seems to disappear and become a good SWR reading when you bring it closer to ground.

When you bring a horizontal antenna close to ground its impedance will change.
This impedance change has altered your SWR meter reading.
This impedance change has counteracted the previous error that was shown on the meter.

It is likely that when the antenna is low that it will take all of the power sent to it , however at such a low height the ground effects will cause an extremely distorted radiation pattern and overall performance will be low.

Another tip ,, dont get fixated on SWR meter readings.
SWR meters do NOT give any indication of antenna efficiency....
In fact SWR meters are very poor tools to use for antenna tuning.


The correct way to tune an antenna (dipole etc) is --

1. Check and correct the frequency of resonance with the aid of a DIP meter.
2. Check and correct the reactance with the aid of a Noise Bridge., the antenna will now be 'resonant'.
3. From the noise bridge impedance display you will now know the antennas impedance ,, change that to match the feedline (often 50ohms) with a matching device at the antenna.
ALL DONE 


With regards to using a tuner....don't use them on antennas that should be self resonant on the frequency of operation.
If you have a fault with the antenna tune or match , then fix it at the antenna., not in the shack.

Otherwise you are taking a loss (from the tuner) to correct a different problem.(another loss)
That is just loss on top of loss., and even though you will still get contacts it wont be as many as if you sort your problems out the right way.

gregW:-)  OH2FFY