VHF/UHF X-Beam Construction Notes (and HF see update below) – k0emt
I sat down and drew out what I did and thought I’d pass on what I did/found out. The design is from The 1993 ARRL handbook that was given to me by WD0HBX. The x-beam was originally intended as an HF mono-band beam. I used the formulas to build it for 6m. It also happens to work out really well for 2m & 70cm use as well.
The text says that this antenna design will typically have a 6-8dB gain and a forward to back ratio of 20dB. The handbook also states that this design should perform as well as or better than a similar yagi.
Notes: (That will make more sense when you look at a picture.)
f swr
(48.4 - 51.35) <= 2.2
50.110 2.2 420.000 1.3
50.125 2.2 426.000 1.6
52.525 2.5 430.750 1.6
435.000 1.1
144.000 1.1 436.300 1.6
145.050 1.2 442.000 2.0
146.000 1.3 444.000 1.6
146.400 1.4 445.000 1.1
146.520 1.4 446.000 1.5
148.000 1.2
Figure 1: X-Beam Antenna Design Overview
| Color | Part | Description |
|---|---|---|
| Green | Directed Tails | Wire |
| Yellow | Directed Arms | Tubing (Wired together at vertex) |
| Cyan | Project box | SO-239 (Wires lead from here to driven elements) |
| Purple | Driven Arms | Tubing |
| Red | Driven Tails | Wire |
| Blue | Support Cord | Nylon Cord Runs around perimeter zip tie wire tails to this support also used to provide stability |
Figure 2: Marked X-Beam Antenna Design
On air testing has shown that it is indeed directional. Had S-8 noise on discone, switched to beam, now S-3. Conversely, when testing on 6M with a horizontally polarized “local” station KB0QHZ, noted an improvement of 5 S-units when using beam. (cross polarization could come in to play though – the discone is vertical.)
When testing with KB0HNR mobile in Jefferson City, MO I was able to copy him at times S5-9 when the discone couldn’t even hear him. A similar gain was noted when hearing DX when cross-polarization shouldn’t be an issue.
Noted, that when I changed the direction it is pointed wasn’t able to bring up certain local 2M FM repeaters.
Hooked up an ICOM 706mkII, using 20w on 2M SSB made a contact with K9IMX (Lake of the Ozarks), he reported me 57. He regulary works N9WYX, another “serious” 2M ssb station within ~1/2 mile of my QTH and he said he was impressed with my signal.
As a side effect, it seems like the discone is peforming better now than before. The discone is mounted off the top of a 20’ mast. The beam is approximately one foot under it. Maybe, it’s benefitting from some sort of ground plane effect?
Overall, I’m fairly happy with this beam. I have the feeling I will be building another one this year. I’ll use better materials and be more exacting on the next go around.
If anyone decides to build one, please let me know. I’d be glad to help any way that I can and to stick it on the analyzer when you’ve finished construction.
KB0HNR was over recently. We had the antenna hooked up to my Kenwood TS-570S. The 570’s tuner matched the rig to the antenna on 20 and 40 meters. We had a 59 contact into MA on 20m and were able to check into the 3905 net on 40 meters.
Not bad for a VHF/UHF antenna!
I now think that the reason the antenna was working on the HF bands was because it was so close to ground that there were some very strange interactions going on. The antenna was on a ground mounted 5ft Rohn tripod, with a 5ft Radio Shack Mast, Rotor & 4ft PVC mast attaching to the antenna. 2M and 440 were exhibiting good SWR but I was having a heck of a time with 6M. 6M would however tune.
Presently, I have moved the antenna a top a ~25ft Rohn 25G tower. As currently configured I have a 1.1swr for 144.2 and a 1.8swr for 432.1. 50.125 is currently showing a swr of 8.3, Rs=8 and Xs=17. Just this last weekend I added a 10’ section to the tower increasing it to 25ft. I believe before I had done this that my swr was < 2.0 on 6M and on 2M,440 it was >1.5 but <3.0. I am coming to the conclusion that this antenna is very sensitive to it’s height above ground.
For now, I plan to leave it as is, (I don’t climb), and use the internal tuner of the TS-570S to make up the difference. Which it does just fine. By summers end I hope to add another two sections to the tower and a hazer. At that point in time I will try to adjust the antenna or make a matching circuit.
As an aside, the 570 will now tune the beam for 10M.
Beam is now at ~50ft. It is performing well. Frequency and corresponding SWR as measured with MFJ antenna analyzer.
| Freq | SWR |
|---|---|
| 21.450 | 2.6 |
| 21.3– | 2.8 |
| 21.0– | 3.3 |
| 18.168 | 2.7 |
| 18.068 | 2.6 |
| 14.350 | 1.8 |
| 14.225 | 1.9 |
| 14.150 | 1.9 |
| 14.025 | 1.8 |
| 10.15- | 1.5 |
| 10.1– | 1.7 |
| 7.3– | 5.5 |
| 7.225 | 6.2 |
| 7.150 | 6.8 |
| 7.0– | 8.2 |
| 4.0– | 8.4 |
| 3.85- | 9.5 |
| 3.75- | 10.5 |
| 3.5– | 25.5 |
| Freq | SWR |
|---|---|
| 446.0– | 2.0 |
| 432.1– | 1.4 |
| 148.0– | 2.5 |
| 147.0– | 2.0 |
| 146.0– | 1.6 |
| 145.0– | 1.5 |
| 144.2– | 1.3 |
| 54.0– | 1.4 |
| 53.0– | 1.6 |
| 52.525 | 2.2 |
| 51.0– | 3.2 |
| 50.125 | 3.4 |
| 29.6– | 3.7 |
| 28.885 | 4.6 |
| 28.5– | 6.0 |
| 28.3– | 6.6 |
| 28.0– | 7.5 |
| 24.99- | 4.3 |
| 24.93- | 4.1 |
| 24.89- | 3.9 |
I could not get my Kenwood TS-570SG to force feed the X-Beam on 28.337. It did match it on 29.6. The rig will also not make the match on 40 Meters. Obviously it won’t make the match on 80 or 160 either.
It is VERY important that the arms be of a significantly larger diameter than the tails. More info on specifics can be found at LB’s (W4RNL) page below.
Here are some additional web resources for your perusal.
Figure 2 above illustrates the marked X-Beam Antenna Design. The front yellow and green are a directed element, while the rear pink and red are the driven element.
The thin wire does not pass through the larger tubes.
For the directed element (passive), the two pieces of tubing are connected together with a wire jumper. The green wire tails are connected to yellow tubes at the end using machine bolts/hardware or rivets.
For the driven element (active), the feed box with SO-239 has the shield connected to the end of one tube (pink) and the center pin to the other tube (pink). The wire tails (red) are bolted or riveted to the tubes. A 16AWG wire was used for this connection.
| 928 5 element colinear | |
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1" aluminum tubing was used for the large sections. 12 gauge stranded copper wire with ring connectors for the small wire sections. The ground plane wires are from brass rod. Ring connectors were soldered on to the brass rod. The rods were riveted to the base section of tubing. All stranded wires were riveted to the larger aluminum tubing. The coax used was Radiall-Larsen Dual shield RG-58. Peformance is much better than the three quarter wave below. A station that had quite a bit of QSB on them with the 3/4 wave was Q5 with this antenna. With the SMA3 they could not be heard and they couldn't hear me either.
I really need to go back and rebuild this antenna. After revisiting Ross's site below, I realized that my first element is improperly built. I should be feeding the first fat element in the center. I also did not utilize the 75ohm quarter wave match that he does.
I built a similar 3 element colinear for VHF. I tried the techinque of feeding it through the bottom section to act as a decoupler trick and it doesn't appear to work all that great. I'm going to try it out again with a 75ohm quarter wave match. This site was the inspiration for this antenna. I just sized things for 928Mhz. |
| 928 3/4 wave | |
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This antenna was built with all scrap box parts. The top piece of aluminum tube was left over from an antenna trimming/conversion project. The bottom piece of tube was from scrap that was cut off of another antenna. The RG-58 a/u with molded BNC was another piece of scrap. As well as the PVC tub that serves as a support. The ends of the coax had ring connectors soldered on them. Both piece of aluminum tubing were drilled through the pvc support. Then the coax ends were connected to the aluminum tubing with aluminum rivets. (The tape is added for waterproofing and aesthetics.) It performs better than the Comet SMA 3 it replaces. |
I wanted to have a resonant antenna on 160M so this is what I came up with.
Materials
Construction is pretty straight forward
Notes
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k0emt's 6m/2m whipI used a completely threaded 3/8"x24 TPI bolt with an Allen style head and a lock washer for mounting the cobalt steel heavy duty spring to the mount. Next is a lock washer and a medium duty stainless steel spring. Then a 3/8" x 3" extender topped with a barrel connector with locking nut. A whip adapter with stainless steel whip tops it all off. The radios in my truck are mounted on a "Shelf-it" brand over head shelf. I went with this brand because the fabric covering is actually fabric particles that are blown on to an adhesive coated aluminum shelf. (That way you don't rip all of the shelf material off when you are drilling holes!) |
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SummaryThis is my 80M "field expedient" antenna. I primarily use this as a NVIS antenna with my FT-817 QRP rig.Materials:
Construction:
Notes
WA2ZKD suggested the following (edited):
Variations
Reports from Builders
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Numerous people on several yahoogroups, of which I am a member,
have commented about the need for a flexible HF antenna.
This is a prototype antenna I built up from material on hand.
The antenna shown has approximately 20" of tubing.
The analyzer says it is resonant on 6M and 70cm.
On the air tests with the Yaesu FT-817 show this to be true
in operating as well.
Variation: use a section of 3/8" x 24TPI bolt instead of the aluminum wire. Warm the vinyl so you can work the bolt head into the tubing. Use a ring connector on the wire at the bolt end. Tape the wire to the tubing around the bolt head to help secure everything.
If you are only using the stock antenna that came with your SWL radio, Yaesu VX-7 or Kenwood TH-F6/TH-F7 you are missing out on a lot. This page describes a couple of parts box medicine bottle antennas that you can build. Specific values are not that important. Especially for receive only use.
In one example the coil was wound on 3/8" plastic tubing. In the big bottle example the coil was wound on ~1/2" plastic tubing.
The ground side of the capacitor is soldered to the ground of the BNC connector. The positive side of the capacitor takes 5 turns around the toroid and is soldered back to itself. The center pin of the BNC connector takes 5 turns around the toroid and then continues on to the wire wound inductor. From there the antenna continues with an attached piece of wire.
Toroid, capacitor and inductor specifics are not critical as this is intended primarily as a receive antenna. You can check your resonant frequency with a tool like the MFJ-269. This simple antenna will greatly increase your enjoyment of HF SWL with your TH-F6a.
Give this simple parts box antenna and matching unit a try and you'll be surprised. I'm only using about 6Ft of wire after the inductor. For the larger coils I used a plastic form and ~22AWG magnet wire. For the smaller coil I used a piece of tubing used on water systems with very fine magnet wire. Materials and values are NOT critical for the most part. The Important thing is to have fun!
The biggest thing is to have fun and experiment.
Drop me a line and let me know how it works for you.
How long is the counterpoise? The overall length including the "pigtail" that is attached to the antenna bracket is the appropriate length for the frequency based on Bonnie KQ6XA's research. Here are some excerpts from the Counterpoise_Radial_Length file provided by the HFPack group.
The problem of predicting or computing the length of a resonant wire gets more complex when using dragging counterpoises and very low radials or radial wires laying partly on the ground. Because of proximity to the earth surface, the wire needs to be shorter. Earth (soil) conductivity affects the resonance, so different soil types may require different length counterpoises. Generally, the more conductive the soil, the shorter the counterpoise.
I've found empirically that a pedestrian dragging counterpoise wire can be about 10% to 25% shorter than the standard quarterwave formula predicts, and the whip will usually tune to a fairly good 50ohm match. Insulated wire with low ohmic resistance should be used. For best dragging quality, Teflon or slick PVC-jacketed or oil-resitant multistrand wire is best. For safety while walking with a dragging counterpoise, some sort of slip-connector or an alligator clip should be used so that the connection will break apart if the wire is caught by a rock or vegetation.
|BAND| FEET | |----|------| |10m | 7.4ft| |12m | 8.0ft| |15m | 9.9ft| |17m |11.0ft| |20m |14.0ft| |30m |18.5ft| |40m |26.3ft| |60m |34.3ft| |75m |45.4ft| |80m |49.3ft|
I am using a bass pro big country pack. I picked this backpack for it's external frame, hydration pack and because it fit me! The frame and padding are set up really nice. They do a really good job of letting air circulate around. I was really surprised when I felt a breeze come across my back while wearing it.
I found some great brackets at a truck stop for mounting antennas. They are Barjan 300-306, "GM Models" prior to 1990 Mirror Mount. I did grind down the part of the bracket near to the pack.
One mount is configured with NMO so I have a lot of versatility with it. Using adapters can go to UHF or BNC F. Coax is terminated with BNC.
The other mount is standard 3/8-24 with a quick-detach stud. Connected a detachable counterpoise wire to one of the nuts on the mount.
I use a Kenwood TH-F6a mated with a Comet SBB-5 dual band antenna. The rig was an easy choice. The main factors were simultaneous dual VFO's, all-MODE recieve and excellent battery life. I can keep one VFO on a local repeater or simplex frequency. The other VFO can be monitoring 18.157.5 USB. So, then I don't drain the HF rig's battery in RX.
The antenna was a tough choice. In the end I went with a Comet SBB-5 because I like the black color with the pack, the height is just right, flexibility is good and I had one on hand. Why do I care about height for this antenna? As you wear the pack it is on the right side. I did this because typically a brush/trees that hang over the trail are lower on the outside. I'm going to see how this works out, but I will be very tempted to get one of the new Comet EX-510B NMO 6/2/440 antennas. It doesn't take much additional antenna on the F6a to really bring up the receive on HF.
The Yaesu FT-817 is the rig that I use on the HF/50 side of the house. I use the homebrew vertical for the antenna.
I have a length of 14 gauge wire that has ring connector on one end and a female spade connector on the other. The ring connector is attached to the antenna bracket. The wire is routed down around the outside of the pack to where it terminates in the female spade connector. I then attach a counterpoise wire that has a male spade connector on the end. With this arrangement if the counterpoise gets hung up on something, it disconnects. Otherwise, the wire could pull on you causing you to lose your balance and fall. Not a good thing.
Now, the question becomes where to put the quick disconnect? Because of the way I have my wire routed I opted to put it a couple feet away from the bracket, past the end of the pack. My thought is to put the quick disconnect far enough out that you can easily reach back, grab the wire, pull the connector around in front of you and plug the dragging part back in. Saves you from having to take the pack off or from practicing to be a contortionist.
Also, take a piece of flagging tape and tie it to the part of the dragging counterpoise that is by the quick disconnect. Now when it comes unplugged you'll be able to quickly spot it. Optionally, use a brightly colored wire. But be prepared to have LOTS of people tell you, "you're dragging a wire."
I've also added a yellow ribbon (HFPack identification) to the VHF/UHF antenna. The yellow ribbon is also a traditional indicator of support for our troops. Thin, ribbed cloth type, melted the ends to keep from fraying.
On my HF antenna I added a US flag to the top. I used a flag that came on a round tube. Cut the top off the tube and again below the flag. Secured to the whip by putting zip-ties in place above and below the flag. HINT: wrap the zip tie twice and through itself to really snug it up! Now the flag waves freely when /PM.
When in an urban environment the ribbon and flag also serve as added visual attention getters. Especially handy when you're in hilly terrain. I sometimes find myself out during the twilight hours. For those times I have an LED flasher on the back of the pack. I also keep an LED flashlight in one of the pack pockets. Plan your route, follow your route, and make sure someone knows you're route and expected times. Pretty much your standard hiking/backpacking safety rules apply.
Be safe and have fun! 73 -- de Bryan, K0EMT
The lowfer kit - a bit fuzzy SRI!
Close Up - very sharp!
Numerous people on several yahoogroups, of which I am a member, have commented about portable HF antennas being a compromise in performance versus convenience. I believe this antenna slams down the scale on the side of convenience for operating 160M and 80M portable.
The analyzer showed low SWR on 160M and 80M. My FT-817 agrees.
40M and 30M show a bit higher SWR on the analyzer.
The 817 shows 3 and 4 bars respectively.
I was testing with 2.5W out CW.
| K0EMT with 20M Rigid Dipole | 20M Rigid Dipole details |
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This antenna is designed to be mounted off the side of a tower. The idea is to run the arm through the tower, bracketing to the far side of the tower. The middle of the arm should be zip tied to the tower. In the "laboratory" this antenna showed a VSWR of <= 2.0:1 from 136-153.1Mhz. With 1.1:1 at 144.2. This is good since the primary intent is to use it as a packet antenna. It also tested well for the entire 70cm band. |
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By the way, I will be going to black UV resistant ties before installing permanently.
I designed this this mast mount because I wanted to be able to rapidly deploy a mast mounted antenna in a location that didn't have other supports available.
After having practiced with this mast mount, I would likely have the bottom collar welded to the rest of the frame. Although that doesn't lend itself well to transport. So, it's a toss up.
John, AA0ZC built the mount for me. If you would like him to build one for you, contact him directly for an estimate.
* End Cap & Mast
** Generation 1
Bottom has a 3/8" x 24TPI bolt in a PVC end cap.
Then a section of 1" aluminuum tubing.
Overall length and coil weight of the Gen 1 have relegated
it to a primarily portable HF vertical role.
** Generation 2
Changed to a metal end cap, filling in extra space with PC-Metal Epoxy.
Then a section of 1" aluminuum tubing.
Mast shortened for mobile operation.
** Generation 3
Copper tubing mast design. Much nicer appearance.
Field use demonstrated that the copper is too weak for extended use.
** Generation 4
Fiberglass tube w/epoxy filled PVC cap
* Coil
A smaller section of PVC slides inside of the mast.
Coil is wound on the PVC.
** Generation 1
Topped off with another bolt that has been pressed and epoxied into
the PVC tube. Then a whip tip adapter and a whip.
Taps at various places, required tuner.
Antenna ends up ~9'9" tall. With full coil resonant at ~6.9Mhz.
Bypassing coil it covers the entire 10M band < 1.8:1.
** Generation 2
The bolt is simply put into the PVC end cap.
Nut and whip tip adapter arrangement.
Taps are located for resonant frequency, no tuner required.
Coil shortened for better mobile operation, only goes to ~10Mhz now.
** Generation 3
Nut and whip tip adapter configured with Quick Detach spade connectors.
After 20M tap switch to smaller gauge wire, allows for 40M operation.
** Generation 4
In progress, going to fiberglass coil form.
Most likely will use PowerPole connectors instead of spade connectors.
* QSO's
First Contact, Generation 1
05 Feb 02 1035 CDT 28Mhz EA3XA 58 58 Jose - Barcelona Spain
w/ICOM IC-706 mk II @ 100 Watts
* 80M
Use a wire with Max Coil for 80M, works well for Section Traffic Net.
Better results on 80M can be obtained by using a 56" extender
below the coil. (Stationary use only!)
* Costs
Al Tube ~$4 (~$12 for 8ft pc)
PVC Tube $1
Wire ~$4
Incidentals - Epoxy, Hardware, Ring Connectors, tape ~$2
3/8" Hardware - ~$7
Whip - ~$7
Total ~$25
10 Bands for about the price of 2 mobile monobanders.
* To Be Done
** Document
Where tapped, how chose where to tap.
How tapped, 14Gauge wire
length of each section
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