KI6ZHD's Installation of an Alpha Delta DX-CC parallel dipole Antenna

Updates:

• 03/15/10 - Talked to Alpha Delta
  Spoke to Dan at Alpha Delta about the results on this page. He felt that the trees are the cause of the high SWR issue but the antenna and the RFI choke look good. He specifically called out my MFJ-969 Deluxe Versa Tuner II roller inductor tuner (picture below) as not having enough inductance and capacitance to properly deal with high SWR specifically on the high bands (80 and 160m). Go figure considering I was going with recommendations from folks recommending roller inductor tuners and a higher wattage to avoid arcing, etc. Still sounds like roller inductor tuners are the way to go though.. maybe just not MFJ ones. I know...SHOCKING! Alpha Delta specifically recommended Palstar and LDG tuners and I've heard good things about SGC as well. Beyond that, Dan recommended that I might drop the left leg of the antenna (the one in the clear) to be 10' off the ground (no more than 45 degrees from center) similar to an inverted V. This should lower the SWR a bit. If that doesn't help, he recommended to shorten each end of the antenna 12" to bring the 80m band up to say the phone portion.

• 03/14/10 - original version

• 12 gauge solid copper wire with insulation for all three parallel dipoles
• 2-3 inches of space between each dipole via PVC spacers
• a flap top orientation should work well but each leg at 45 degrees from the center point is ideal (?more omni-directional?)
• trees LOWER resonance

• top dipole serving 80/40/15m - full wave for 40m : 41 feet long PER side
  - 80m is a high-Q antenna giving a limited usable bandwidth of about 65Khz @ ~2:1 SWR
  - air coils near ends use 18 gauge enameled solid copper wire
  - 15m band uses the third harmonic of the top dipole
  - 15m will have an upward resonance shift

• middle dipole serving 20m - full wave for 20m: 16 feet PER side

• bottom dipole serving 10m: 6 feet PER side

  Supported band	stock resonsant freq	Bandwidth	notes
  80m	3750-3800	65Khz @ 2:1SWR	Hi-Q design
  40m	7150	?full band?	full wave dipole
  20m	14100-14150	?full bandwidth?
  15m	21450	?unknown?	3rd harmonic of 40m thus has an upward resonant frequency shift
  10m	28200-28300	?unknown?

Suspension:

Each end of the DX-CC antenna is held by a pair of independantly tied Dacron ropes to the end insulator. The dacron ropes are run through a pully and tensioned with a ~11lbs weight near the ground to allow for wind loading, etc. The estimated height is 50'. It's unclear if 11lbs is too much weight.

Radio connection:

The center point of the antenna is fed by about 100' of true TimeWave LMR400 coax, into a quality SO-239 barrel, into an RFI choke and into the DX-CC center assembly. All SO-239 connections are weather sealed with a combination of a double wrap of true 3M/Scotch 33 electrical tape, a healhy coat of dried liquid electrical tape, and another double-wrap of Scotch 33 tape.

RFI Choke

The RFI choke consists of 3 feet 3 inches of RG-213 low loss coax with PL-239 connectors on each end. The coax loops through the TOP 4 ferrites four times and bottom 4 ferrites three times. The loops of the coax are as tightly wound as possible without exceeding the coax bend radius. The ferrites themselves are lightly zip tied to maintain the seperation of the top and bommon cluster but within each cluster, they are not tightly ziptied together to minimize any heating/cooling issues. Each individual feritte is painted with a basic 5minute expoxy everywhere except the inner part to minimize chipping, etc.

Top view of the choke:


side view of the choke:

Here is an initial SWR sweep of the DX-CC antenna as it stands today: [ xls ][ pdf ]

Antenna Pictures:

Image #1 - This overview picture shows the installation as it stands today. The tree on the left (tree #1) is the left-most anchor tree. Tree #2 is the center point of the antenna and is a bit lower than tree #1.

Image #2 - This is the right-of-center point antenna installation overview shot. Notice that from the center point to the last tree (tree #5), the 80m dipole goes up a bit. Not sure if this is a problem

Image #3 - This shows the center-point of the antenna, the choke, and the parallel dipoles. This pictures shows the spacers being a bit tilted but it's not clear if that's a problem

Image #4 - This shows the center point of the antenna next to tree #2's trunk, the RFI choke, the pulley, etc. It should be noted that the RFI choke is also tied into the center-point's hanging hold to minimize any coax connector strain between the center point and the choke. It's unclear if this close proximity is a problem.

Image #5 - This shows the left-side of the parallel dipole is not 100% vertical. Not sure if this is a problem

Image #6 - This shows the right-most air coil on the 80m dipole and it's proximity to the tree trunk, etc.

Image #7 - This shows the MFJ 969 Deluxe Versa Tuner II roller inductor tuner that can't handle high SWR antennas on 80 and 160m. Something to note for other HAMs as this unit supports ladder and random wire modes yet there is NO way this tuner can deal with them.

09/29/10