Alpha Delta DX-EE High SWR on 40 Only

[shortwaver]

Trying to understand this issue that I'm having with an Alpha Delta DX-EE fan dipole.

SWR on 20, 15, and 10 meters are all acceptable, close to 2.0
SWR on 40 is 20.

The antenna is in my attic. There are no ducts in the area and no metal nearby.
Antenna height above ground is 10 feet to 18 feet due to the house being a split level with the front yard being higher than the back yard.
Two different, known good (using on other systems) feedlines tested with same result. One was a RG-6U and the other is a RG-213U.
Feedline run is under 30 feet.
I have confirmed the lugs (that connect the elements to the main housing) are tight.

20 meters works fine. I don't use 15 or 10 to have any practical experience with it.
40 meters would be great but with a SWR of 20, it's unusable.

Anyone have any ideas of what I could try?


Thank you and 73
Shortwaver

 

[prcguy]

Can you sweep over a wide range beyond 40m to see if the SWR dips out of band?

 

[K4EET]

Hi @shortwaver, I have an Alpha Delta fan dipole as well. Nice antenna. Some thoughts:

1. What are you using to measure the SWR? Please provide make and model number of the instrument.
2. What @prcguy said would be great if what you are using in #1 can perform a sweep.
3. Stick with the RG-213/U since your antenna has a balun designed for a 50 ohm feedline. RG-6/U is 75 ohms for CATV systems.
4. What is the average SWR in the CW and phone portions of 40, 20, 15 and 10 Meters? Particularly interested in the 40 and 15 values since they are on the same wire. You should have 3 dipoles; not 4 over and under each other (the fan). Would like to see how the whole antenna is performing to rule out water in the coax and other nasty things like that in the common areas.
5. If you cannot sweep the 40/15 wire with what you have, do you know anyone with a NanoVNA or an antenna analyzer?

Not much else we can do until you get back to us with some additional information.

73, Dave K4EET

 

[shortwaver]

Can you sweep over a wide range beyond 40m to see if the SWR dips out of band?

Hi prcguy.

I did run a couple of sweeps off of both ends of the desired frequencies, looking for exactly what you mentioned about the swr dipping. There was no changes on both sides, still poor.

Thanks!

 

[shortwaver]

Hello K4EET!

1. I am using a RigExpert model AA-230 Zoom.
2. I have performed side sweeps and the swr stays mostly the same.
3. I agree and am sticking with the RG-213U, which has been used for all the testing.
4. At this point, I'm concerned with using my Icom 7300 to tell me the SWR while using CW as I believe it may damage the radio.

I'm at the point now I think that I'll either just use it on the one good band, 20 Meters, or I'll take it down and test it strung out.

Thanks and 73
Shortwaver

 

[prcguy]

The 40m leg has a loading coil to shorten the antenna and the 40m leg is also the 15m element resonating as a 3/4 wavelength. If 15m has a reasonable match I would look at the surroundings and nearby wiring or metal lath under stucco, etc.

Can you hang the antenna outdoors somewhere for a temporary test?

 

[shortwaver]

Great thought. I will check the match on 15m later today.
I don't know if the close proximity to the roof rafters is a factor, the 40m and 15m section is about 5 inches away from them at the ends, but the manual says to give yourself 2 feet plus away from building material. This may be more of a liablity issue than a functional issue.

 

[shortwaver]

I was able to check the match just now and 15m had a swr of 2.1. Not even good but much better than the swr of 16 that is on 40m.
So you're thinking that the coil, or something close to it may be causing the issue, and I'm with ya. I will take a closer look.

73