Many thanks to Barry (KU3X) for sharing the following guest post originally posted on his website:
Product Review: PAC-12 Portable Multi Band Vertical Antenna
by Barry G. Kery, KU3X
I am always on the hunt for a better mouse trap. Dave, NB3R came across a great multi band vertical antenna for portable operating. It’s a, “ PAC-12 7-50MHz Shortwave Antenna “ found on AliExpress.com.
The PAC-12 antenna is designed to operate on any frequency from 6 meters down to 40 meters.
Numerous manufactures make multi band vertical antennas designed to be used for portable operating. Some have quality issues and others may have performance issues, or both? Any hunk of wire or aluminum will radiate if RF is applied to it, but how much will be radiated is the question.
When it comes to ground mounted vertical antennas, one major factor that effects performance is the ground radial field. The PAC-12 comes with a long ribbon cable that you will have to separate each wire and cut to a quarter wave length per band of operation. There are ten wires within the ribbon cable. The length of the ribbon cable is 18 feet. This is too short for 40 meters but perfect for 20 meters. I made four 35 foot long radials out of some wire I had laying around the shack. This will increase the performance on the 40 meter band as well as making a better match. Spread the radial wires out equally around the base of the antenna. Since the radials are not elevated, they do not have to be tuned but it does make for a better match.
The stake is strong enough to support the entire antenna, even on windy days. The feed insulator has an SO-239 for connecting your coax. The feed insulator must be attached to the ground stake correctly. Make sure the writing on the insulator is on top of the SO-239 and the black portion of the insulator is attached to the ground stake.
Most manufactures, not all, use a tapped base loading coil to make the antenna resonant on numerous bands. On a quarter wave antenna, the wire or aluminum closest to the feed point of the antenna is the current portion of the antenna and the current portion does the most radiating.
By base loading the antenna you loose the most important part of the antenna which directly effects the efficiency of the antenna. The PAC-12 has a 4 foot mast that goes between the feed point of the antenna and the tapped loading coil. Each section of the mast is one foot long. The threads on each end are metric, 10 mm.
The contact slider is very easy to slide up and down, by hand, for changing bands. Look closely at the fourth turn on the coil from the left hand side of the assembly. It is colored brown. That shows you where the tap is to be place to operate on 20 meter. Looking at the right hand side of the coil you will see, around 10 turns from the end another wire is colored brown. This shows where to place the contact slider for 40 meters. We found these two tapes to be spot on. For thirty meters, the contact slider is placed close to the center of the coil. If you want to operate on 17 meters, move the contact slider to the very top of the coil and then shorted the telescopic whip around eight inches. Keep retracting the telescopic whip to raise the operating frequency.
The overall length of the antenna fully assembled is 13 feet. Dave and I tried his antenna on four bands. We were able to get a low SWR on all four bands.
The PAC-12 is advertised to handle up to 100 watts. The quality of this antenna is far superior compared to most of the commercial antennas that I’ve seen that are made in the USA. Most, not all.
DX Engineering sells this product for around $209. Dave purchased his off of AliExpress. I ordered one for myself off of AliExpress and I paid $125 with free shipping. It took two weeks for it to arrive. Search AliExpress, “ PAC-12” and you will see numerous sellers. Prices range anywhere from $114 to around $138.
Just a note on ground radials:
When radials are laying on the ground, they don’t have to be tuned. You should try to cut them fairly close to one quarter wavelength, but it’s not critical. You want to lay down as may radials as possible for maximum performance. But if you can only lay down maybe two per band, the antenna will match and work well. To increase the performance of a vertical using radials laying on the ground, you need to double the amount of radials. This will improve you signal by 3 db. Want an additional gain of 3 db, again double the amount of radials. Once you have 120 radials laying on the ground, you have reached a point of diminishing returns.
A different way of improving the performance of this antenna is to elevate the radials. When doing so, the radials must be tuned to the proper quarter wavelength per band. If you erect four tuned radials on the band of operation, you have pretty much come close to maximum performance.