Need help with my new A-D DX-A antenna

[KD8ZCM]

Hello all, I am have an issue with tuning up my new Alpha Delta DX-A dipole sloper antenna. https://www.alphadeltaradio.com/dxabinstructions.html

Followed the inst. to the letter for installing it. I will mention that the inst. are different from what I put up..as the 80 meter part of this is a single wire at 67 ft. and has no coil, the 40 /160 part only has one coil and not two like mention in the inst.

The issue I am having is in the tuning up part. I am using an Alinco DX-SR8 radio going into an MFJ-929 auto tuner and new RG-8 coax. Tunes perfectly on 10, 12, 15, 17, 20, 40, and 60 meters. But it will not tune the 80/75 band nor the 160? I mounted it at 20 ft on my tower down to 12 ft.at the end. Reason its so low is because I want to work my station as a NVIS station for local NTS traffic. Is there anyone who can help with my tune up problem on 80/75 and 160 meters?

 

[prcguy]

How high is your tower? Your particular antenna must be mounted 4 to 6ft below an existing HF beam antenna to provide a capacity hat for the tower, which is half the antenna. Do you have an HF beam antenna and is the sloper mounted 4 to 6ft below it? Do you have any tower guys wires that could be interfering with the sloper? If you can't meet the criteria listed in the instructions it will not work without a lot of custom tuned counterpoise wires attached to the feedpoint and running down the tower and probably across the ground.

In my experience the Alpha Delta coil loaded antennas when working perfectly will have very narrow band width on 80 and especially 160m. Last one I checked was barely usable across 50Khz on 80m and on 160 you can tune it for basically one operating frequency.

For NVIS about 30 to 35ft above ground is ideal because that is about 1/4 wavelength above ground for the highest band (40m) that you will encounter NVIS. That would be for the entire antenna being 30 to 35ft horizontal and when one end gets close to the ground efficiency goes down. 30 to 35ft high will be about 1/8 wavelength on 80m and the wire might as well be laying on the ground for 160 as it will be very grim at best in performance.

If you mount an NVIS antenna lower than about 30-35ft the efficiency starts to go way down on 40m and the other bands which are already compromised due to low height will suffer even more. If this was a receive only antenna then you can lay it on the ground and it can work fine but for transmit you will need to make up for the inefficiency with lots of power.

 

[KD8ZCM]

Thanks prcguy, for your response. My tower is 56 ft. tall free standing no guy wires and I don't have a beam as or yet. I have read that some NVIS setups can be as low as 20 ft. So I will move mine up in the air then to about 40 ft. I am already using a SW sloper there and will swap them. Thanks for correcting my rookie mistakes..

 

[prcguy]

Is the SW sloper running parallel to the amateur version or is it on the opposite side of the tower? They can affect each other and running in opposite directions should minimize that.

The fact that you can match the upper bands and not the lower generally indicates there is insufficient counterpoise for the lower bands. You might try about 65ft of insulated wire connected to the ground side of the feedpoint, running down but away from the tower to the ground then heading away from the tower opposite the sloper. I suspect you will get an instant low SWR point somewhere near 80m and if so you can usually tune that to a specific frequency. If that works you can add another for 160 but it would be about twice as long.

Thanks prcguy, for your response. My tower is 56 ft. tall free standing no guy wires and I don't have a beam as or yet. I have read that some NVIS setups can be as low as 20 ft. So I will move mine up in the air then to about 40 ft. I am already using a SW sloper there and will swap them. Thanks for correcting my rookie mistakes..