Center Fed Inverted V 'HF' Antenna

[Diverdan86]

Good morning!

I had an eventful weekend wrestling with my new HF rig, along with a a new LDG Z-11 Pro II ATU and setting up an inverted V antenna. I'm here seeking advice from pros who might lend their expertise to my current dilemma.

Equipment:

• IC-7000
• LDG Z-11 Pro II ATU
• RigExpert AA-650 ZOOM
• 40' RG8 cable to ATU/radio
• Military surplus 200' Center-fed Dipole Antenna at a height of 34 feet, on a steel pole
• Antenna Location: Situated amidst a forest of towering evergreen trees, with the antenna positioned between a metal-roofed shop and a similarly roofed home (approximately 30' from both). I ran the legs of the inverted V away from the structures, with the ends of the antenna tied to trees about 8 feet in the air.

The Situation:
On Friday evening, I hoisted my first inverted V antenna and connected the rig expert, only to find an SWR of 7.5 @ 28.5 MHz Despite various attempts to adjust by expanding and shortening the ends of the military antenna (I did this by winding it up on the attached insulator spools), I could only marginally affect the SWR, with minimal improvement (+/- 1.00).

Further inspection revealed that SWR on all the other bands ranged from 5 to 8, with the one outlier with SWR of 1.58) oddly at 450 MHz. With time running short, I decided to test whether the LDG could tune up the antenna as is. I positioned everything on a table at about 40' from the antenna feed point, lowered the power on the IC-7000 to 10 watts on AM, and attempted to tune in the 10-meter band, but to no avail. Even after increasing power to 30 watts, the LDG failed to find a match. I then also tried on the 11m and 6m bands with the same result.

As far as reception goes, I scanned for signals for about 5 minutes and I couldn't get anything, though I recognize that this alone isn't conclusive evidence of an issue.

Best Guesses:
Is the antenna setup flawed, or could the LDG just be malfunctioning? I anticipated the LDG should be capable of tuning an SWR of less than 9 or 10 to an acceptable match. I'm considering trimming down the legs of the inverted V, as I primarily intend to use the antenna for 11m/10m and 6m, which should ideally bring down the SWR. However, I'm unsure if I have a defective ATU, the SWR is beyond its capabilities to tune, or if I just have an atrocious antenna/setup and need to start from scratch.

Any insights or suggestions would be greatly appreciated!

 

[prcguy]

What you have assembled is a recipe for VSWR disaster. There are a few options to make a workable antenna like feeding the existing 200ft dipole with 450 ohm ladder line all the way to the shack and using a wide range tuner with balanced input. That should tune and operate 80-10m and radiate just fine. It might also work with a 1:1 balun at the radio end of the balanced line then a very short coax jumper to your LDG tuner but that won’t work on all bands as the VSWR will exceed 10:1 on some bands.

Or you could cut the antenna down and make an 80-10m OCFD which would be about 133ft long and I would use the 81%/19% formula that MyAntennas uses and one of their 4:1 baluns designed for OCFD use. But otherwise a 200ft dipole fed with coax is only going to work around 2.3MHz and a few odd harmonics.

Or make a 94ft long ZS6BKW dipole that will have a reasonable match for the tuner on most HF bands.

 

[Diverdan86]

What you have assembled is a recipe for VSWR disaster. There are a few options to make a workable antenna like feeding the existing 200ft dipole with 450 ohm ladder line all the way to the shack and using a wide range tuner with balanced input. That should tune and operate 80-10m and radiate just fine. It might also work with a 1:1 balun at the radio end of the balanced line then a very short coax jumper to your LDG tuner but that won’t work on all bands as the VSWR will exceed 10:1 on some bands.

Or you could cut the antenna down and make an 80-10m OCFD which would be about 133ft long and I would use the 81%/19% formula that MyAntennas uses and one of their 4:1 baluns designed for OCFD use. But otherwise a 200ft dipole fed with coax is only going to work around 2.3MHz and a few odd harmonics.

Or make a 94ft long ZS6BKW dipole that will have a reasonable match for the tuner on most HF bands.

Awesome, thanks prcguy. So basically it was the 50 ohm coax in conjunction with the extreme length of the antenna that did the antenna in, thus the need for the 450 ohm ladder line + balun as designed. That or it needs to be a shorter /different design antenna. I'll have to research the affects of ohm on antenna system. Thanks again

 

[prcguy]

A random length antenna can have an impedance ranging from maybe 10 ohms to past 2500 ohms, way out of range for an LDG type tuner even at the antenna. Coax loss goes through the roof when operated under very high VSWR but 450 or 600 ohm line does not, so that is a way to address some problems. The major hurdle is finding a tuner that is compatible with the balanced line.

A good ferrite 1:1 balun can force unbalanced coax and radio to play nice with balanced line but its hard to say if your LDG tuner will match it everywhere. If you can pick up some balanced line and a 1:1 balun cheap I think it’s worth a try.

 

[n9mxq]

If you're using the reels from an AN-GRA-50 kit (The reels are RC-432/G designator) Keep in mind the manual (http://www.radiomanual.info/schemi/Surplus_Accessories/AN-GRA-50_serv_user_TM11-5820-467-15_1961.pdf) states to set the reels for a Half Wave antenna..

I've used these reels at several Field days without issues. I have 2 sets, and the AN/GRA-50 mast set on my ready in a moments notice shelf in the garage.

 

[Diverdan86]

This is awesome thanks for the resource! I think mine might be the same type, but a generation or two after the reels. Mine are connected to wishbone type keepers/insulators. I could never find a model number to look for the original original manual. If this is designed to be a halfway of that changes a lot, I may try recalculating, bringing it lower to the ground and reducing the amount of coax to the center feed.

 

[n9mxq]

These are the ones I have.

 

[Diverdan86]

These are the ones I have.
View attachment 160385

This is what mine mil. dipole looks like with the wires on on the wishbone insulators, and the package it came in