View Full Version : How long should a mast be?

09-30-2014, 02:35 AM
I have a 5/8 wave Mk1 Station master antenna on a mast up the side of the house witch makes the matching coil at the base of the antenna about 9 feet away from a steel roof.

I set it all up and the SWR was 1:1 so I took the wooden box I was standing off the roof and the SWR jumped up to about a 2.

If I got a longer mast would this fix this problem? if I push it up another 10 ft?

09-30-2014, 09:22 AM
I don't under stand the bit about the wooden box. Check your SWR while your body is no where near your antenna.
I lived in a house that had a sheet metal roof and I set a 5/8 wave antenna dead center of the roof and tied it in place using poly rope. Best base station I have ever had. What I did with mine was I measured the Vertical Radiator length and made my mast that length plus five feet. I had a five foot tripod mounted to the roof. It was the best base station I have ever had.

09-30-2014, 04:18 PM
The base of my antenna is close to the tin as my mast isn't very tall, I was using a wooden box to stand on to do some adjustments, got the swr down to 1:1 but when I took the box inside it jumped back up to a 2, I put the box back and it went back to a 1:1.

I was checking the SWR from inside the house, I should probley do what you did and make it taller than the vertical radiator.

I think its getting capacitance from the box and the trees, roof?

09-30-2014, 05:56 PM
That's right. When I tune an antenna on a car all doors are always closed and the vehicle is always clear of overhead wires and buildings. I also keep the helpers either inside the car or at least 50 feet away from the vehicle.

09-30-2014, 06:10 PM
Get it up in the air about 30-40' and you'll be talkin "Live"....

09-30-2014, 11:04 PM
I pushed it up about 5 feet today with another bit of pipe, and it dropped off about 5 swr points.

I am feeding it with LMR400 coax, I am also thinking I have a fault in the coax or the soldered plug.

Tested and cleaned every joint in the antenna and went over it with an OHM meter so that should be good

10-01-2014, 09:47 AM
Push it up a bit more and see what that does for you.

01-06-2015, 04:28 AM
I cut down a tree witch was next to my mast and the SWR shot right up, I also found if I walk on the tin roof I can hear the radio crackle and if I toch the mast it effects the RX to, my mast is too short.

New plan is push it up another 20 feet from the roof, I am going to make a tilt mast so I can tilt it over when it gets windy, it gets real windy here, I plan to weld up a steel pole with a hinge that bolts to the side of the house and I am going to use an old 20 foot ally mast for the rest so I can pivot the whole ally part over, be good for adjustments and make the radiator last longer.

01-08-2015, 05:05 PM
This sounds like a bad ground to the antenna or in between. Used coax with connectors are easy to reterminate if you have enough slack and be sure the bottom of the mast is grounded.

01-09-2015, 02:20 PM
I did find the fly wire to the coil on the antenna had a partly broken joint it had 0 Ohms but i think it might have caused trouble.

The bottom of the mast goes into the ground but I might have to run a wire between the pivot, its all made up and finished, I just need to clamp the antenna to the top and cut down some small trees so i can lower it right over.

01-11-2015, 02:20 AM
Got it all finished, I can put it up and down very fast and easy, SWR is 1:1 where I want it on the band, and I can pin everyone meters who are close by.

01-16-2015, 09:25 PM
Your support mast should be as long as you want, as long as the antenna base is grounded. Some tricks can be done with the length of the mast and the antennas height above earth. Isolating the top of the mast and then connecting the base of the antenna to maniplulate its apparent height above ground. Other tricks with the length of the guy wires between isolating ceramic eggs. This artificial ground is called a counterpoise.