Many thanks to Charles (KW6G) who shares the following guest post:
Product Review: Chelegance MC-750 Portable Ground Plane Antenna, Part 1
by Charles Ahlgren, KW6G
I recently purchased a Chelegance MC-750 portable ground plane antenna from DX Engineering. Essentially, the antenna system provides a ¼ wave portable vertical antenna with 4 counterpoise wires that operates on 20 through 10 meters. The antenna will also operate on 40 meters with the provided loading coil. The manual states the antenna will support 6 meter operation, but no instructions are provided on how to do so. 30 meter operation is not supported. It appears from our initial testing that no ATU is required.
Here are some of my thoughts on the antenna.
The MC-750 comes with the following components:
- GROUND ROD / ANT BASE
- 50 CM ANT ARM
- 5.2 M WHIP
- 7 MHZ COIL
- 4 COUNTERPOISE WIRES (radials)
- COUNTERPOISE WIRE COLLECTOR BOARD
- CARRY BAG
As provided, it is designed to operate on the 40, 20, 17, 15, 12, and 10 meter bands without any modifications. Six meters is also supported per the manufacturers manual, but no guidance on how to do that is offered in that document. However, finding the proper length of radiator for 6 meters should be straightforward using a tape measure to set the proper whip length.
[Update: Chelegance notes that to operate 6 meters, simply extend the last segment only of the whip (see photo) and for 30 meters extend the last four segments of the whip and 15cm on the 5th segment (see photo).]
I checked the ground rod / antenna base with a magnet and confirmed it is made from stainless steel as both components are not magnetic; a characteristic of stainless. Both the ground rod/ antenna base and the 50 cm antenna arm (which was also non-magnetic) had a hefty feel (together, they weigh about 2 pounds), therefore I think it safe to assume that these components are made of stainless steel. Since most ops will undoubtedly use the antenna arm as an aid to inserting / extracting the ground rod into / from the ground, it seems a prudent decision by the manufacturer to have this piece fabricated from a strong, stiff material such as steel. The machine work used to fabricate these parts appears to be quite good – the fit and feel were excellent, with no sharp or ragged edges to cause problems in the field.
I measured the whip while set at the various position marks for 20 through 10 meters. The band markings on the whip were accurate – giving a 1/4 wavelength radiator when combined with the 50 CM ant arm length…On 40 meters, the whip and rod measured about 1/8 wavelength. The required the loading coil needs to be inserted between the whip and the rod (at approximately 1/10 the total 40 meter whip height above the base). If you want to operate this antenna on 30 meters, it appears that you need to provide an extra 1.4 meter of additional rod as a quarter wavelength ground plane at 10.1 MHz requires a 7.1 meter radiator. Six meter operation would require a whip of around 4.7 feet. With the whip fully collapsed, the length of the rod and antenna arm measures 40-1/4”. Therefore, if 6 meter operation is contemplated, extending the whip about 16 inches from fully collapsed should suffice. However, I don’t think that an antenna configuration such as that would be a very good performer unless it were elevated from ground level; or maybe it would be good for a SOTA activation?
Set Up and Deployment
First of all, this antenna deploys like a dream! Seriously!
For illustration purposes, I borrowed the photo above from QRPer.com. It was taken by Thomas, K4SWL, and how he shows the MC-750 deployed at a recent POTA activation at Lake James Park in North Carolina. Note the relative positions of the antenna base/ground rod, 50 CM antenna arm, lower portion of the 5.2 M whip, and the yellow counterpoise wires plugged into the antenna base and laid out on the ground.
I installed the 50 cm antenna rod on the ground rod/antenna base, then used the rod and its red handle to insert the assembly into my backyard lawn. The pointed ground rod went in much easier than anticipated. I then made sure the bottom of the 50cm antenna rod was screwed securely into the antenna base before proceeding further. Next, I unwound and installed the 4 counterpoise wires. As it shows in the photo, all you have to do is lay the wires on the ground and push the banana plugs into the holes provided on the antenna base. No tools required, and no hex nuts to lose in the grass, etc. Wow, how simple and ingenious. Then I hooked up a 15 foot length of RG8 mini to the PO239. I screwed the whip into the top end of the 50 cm antenna rod and extended it to the proper length by using the 14 MHz mark.
I attached my Rig Experts Stick antenna analyzer and took measurements on 20 meters, then went to 17 meters, etc up through 10 meters, stopping at each of the band markings on the whip. Each band checked out nicely and all ham band segments had an SWR curve (as near as I could tell during this quick check) that showed all frequencies were well below 3:1 SWR across each ham band. Then I inserted the 40 meter loading coil and readjusted the whip length again using the manufacturer’s marks. This time the SWR was below 3:1 except for a small segment near the top of the band. I am sure with a little adjustment of whip length, that situation could be remedied. But if you use an ATU unit, why bother?
In summary, this antenna appears to work as advertised.
Tear-Down (aka: Packing up to go home)
The tear down process was just as easy as the deployment. I was surprised at how easy the ground stake came out of the lawn. BTW, I found that if you have a rag and squirt some hand sanitizer on it, the stake cleans up really nicely. If you are concerned about residue from that, just carry a small bottle of 100% isopropyl alcohol electronic cleaner with you.
Wrapping up the counterpoise wires is very easy. Small holes near the ends of the wire collector board provide an easy starting point. You just insert the wire into the hole, wrap the wire around the slots provided and then insert the banana plug into the larger holes provided. Its all very easy and fast to collect and pack up the counterpoises.
While putting things back into the case, it dawned on me that the manufacturer did not provide any protection for the sharp end of the ground rod. Left unprotected, it would not be long before this sharp instrument would work its way through the wall of the carrying case. I went off to the local hardware store in search of an answer. I found it in the form of a 3/8” ID X 1 “ long plastic spacer that just fit snuggly over the end of the ground spike. Problem solved! See the photos below.
What this has led to is that my measurements have basically confirmed what I suspected…Proper length of the whip is achieved by setting the whip length using the specific band marks and then making sure that all sections above that mark are fully extended and all sections below are fully collapsed. The band segments that are within the SWR zone of less than 3:1 are wide enough where you really shouldn’t need an ATU to achieve desired results. Conclusion: It works!!
I don’t have anything to check radiation patterns, but hopefully the manufacturer can provide this info soon.
Stay Tuned for Part 2
I’m going to try and check out the antenna with my KX2 in the near future, but the WX here has not been very good of late with morning temps in the low 30’s and highs near 50F. That’s too cold to comfortably sit for a period of time and figure out what is going on with a new antenna. After I get a chance to complete that assessment, I will gladly share it with you here at QRPer.com.
Some additional Thoughts
While writing this article, a couple of ideas came to mind….
First, the counterpoise wires are just that, counterpoises, and not tuned radials. The manufacturer has provided 4 – 11.5 ft (3.5M) counterpoise wires. If the operator wants to operate from an elevated structure such as a balcony, wooden deck or tower where these counterpoises would be in fact more like elevated radials, then I think you would need to provide a tuned (quarter wave length) set of radials to replace those provided. The close proximity to a ground surface effectively “de-tunes” a radial wire and as such the effectiveness is limited to a close in area such as that provided by the manufacturer.
Secondly, it might be interesting to study the effects of feeding 2 of these verticals in phase about ½ wavelength apart to see what might be accomplished. I say this because it is really easy to deploy one of these antennas, so why not try to deploy a pair if you have the space? And many POTA activation sites probably do. I need to research this more, but 2 20 meter verticals, for example, could be fed in phase with 2 23 foot lengths of RG8 mini each from the leg of an SO238 tee connector with the center going to the radio. As I said before, this may provide some useful improvement with little extra effort.