I wanted to build a lightweight yagi for portable operation with my SATNOGS Az/El rotator. I surfed on the web and I found the reference site for yagi builders: DK7ZB. In the 2m/70cm-Yagis ultralight session, I found a lot of pictures of very interesting home-made yagis. I discovered that some pieces like central dipole insulator and elements supports are available on Tino’s Funkshop online store (former NUXOCOM.de) and I also discovered that, besides single yagi parts, also complete antenna kits are available.
The material for lightweight yagis is very common, so I tried to compare the price of the Tino’s Kit for 2m/70cm 13 elements Lightweight Yagi kit with the price of the same parts available on my local or online shops. I made a Bill of Material in excel with prices and… the Kit wins! Moreover, I would spent much less time for collecting all the parts and I would have the custom central dipole insulator, which is the most difficult part in my opinion.
I ordered the kit for only 21,49€ (!), payed with PayPal and I got it in a week . The shipment expenses outside Germany are about 15€ and the courier is DHL. In case of small purchases, the shipment is not negligible. Anyway, The packaging was perfect and tha materials inside were unharmed. The kit content is shown below:
The kit is composed by the following parts:
- PVC tubes for Boom, 20mm diameter
- 20mm PVC Clips, for elements support
- 3,2mm aluminum rods, for all elements except radiator
- 4mm aliminum rod, for radiator element
- 7.5 x 4.5 x 4 cm PVC box, for feeding point
- N panel connector
- Small piece of 16mm PVC tube for RF choke
- Small Piece of RG188 cable for RF choke
- 2 metal lugs to be soldered to RG188
- brass terminal strip with screws, 4mm inner diameter
- All needed screws
- Detailed instructions and datasheet
I’m going to describe main steps for building the antenna
- Cut all the elements to the lenght indicated on the datasheet. Be precise at mm! After the cut, remove the aluminum burrs using a flat lime.
Since the VHF reflector is longer than 1meter and the aluminum rods are 1m long, it’s necessary to lengthen it with one rest of piece from other reflectors and using the mammut connector, as the image below:
2. Drill holes in the PVC clips using 3,2mm tip. You can also try to use a 3mm tip and enlarge the hole moving slighthly the drill back and forth. In any case, you can use some glue if the element will not stay in its position. I used a stand for the drill, in order to to perpendicular holes. Anyway, don’t care if you don’t have a stand and the holes are not perfectly parallel to the clip edge, you can do small rotation once the clip is mounted on the boom.
3. Let’s insert the elements in the clamps and mark the element name in order to make the positioning easier.
4. Now, let’s proceed to the most particular part, the feeding point of the dipole.
First of all, the central hole of the insulator shall be enlarged with a 4mm tip:
Then, 2 holes of 4mm diameter shall be made on the sides of the PVC box. The caliper helped me for calculating the exact position. The, the two half dipoles can be pushed inside the insulator, passing through the box walls:
4. Now, two holes of 2,5mm diameter shall be made in the aluminum, using the insulator as guide. Don’t push too much the drill, otherwise the insulator will be ruined!
Now, the two metal lugs can be fixed on the dipole halves by two 2,9x9mm screws:
5. Now le’ts install the N socket connector to the other short side of the box. The connector has two flat notches in the threaded part in order to avoid rotations, so I suggest to drill a 11mm hole first, than work with patience and files (flat and round) as long as the connector fits inside the hole.
6. Now it’s the time to build the RF choke. Let’s drill two 3mm holes in the 16mm PVC tube and do at least 5 windings of coax cable. In my case, I did 6 windings.
Now we have to solder the coax on the dipole lugs and to the N connector. Be patient, because there is not too space inside the box. Nose pliers help in this case. Keep the unshielded part of the cable as short as possible. No matter which conductor you solder on left and right side.
7. Now let’s mark the position of the elements on the boom
This is the final result. The antenna is laying on the table of my Lunchroom. Not too bad 🙂
Since the antenna has an insulating boom, also the supporting tube should be not conductive. I had a 40mm PVC pipe in my garage, so I built this simple 90 degrees support using a small piece of plexiglass, a couple of clips for 20mm tube and a couple of clips for 40mm tube:
Then I started the first tests of my antenna. I put the antenna in my garage (it would be better to work in open space..):
The first check, using default design dimensions, showed this situation for 2m and 70cm:
As you can see, it’s not too worth for the beginning, so it means that I did a good job.
For both bands, I placed three markers: red at the beginning of ham band, green at center and blue at the end. The span is greater than the usable bandwidth in order to have a better understanding of the antenna behaviour.
As suggested on the manual, I started to tune the VHF resonance, so I started to cut 2 or 3 mm at time on both ends of VHF radiator. The resonance vary quickly with the lenghts, so be patient and don’t exceed with the cut lenghts!
At the end of the tuning, I got 980mm. The starting design lenghts was 995, so I cut 15mm. The resonance is shown below. It’s not perfectly centered at 145, but the SWR is <1:1.3 across the whole 2m band, so it’s ok for me:
As suggested by Nuxocom, I started to move the Open Sleeve radiator of 70cm for UHF tuning. The open sleeve is the passive element which is very near to the 2m radiator, and it’s a passively coupled radiator excited by the 2m radiator. I didn’t lower the resonance as much as I wanted in this way, so I started to cut the open sleeve (it’s allowed by nuxocom). At the end of tuning, the open sleeve was 320mm. The desing length was 329mm. The final situation is shown below:
The VSWR response is very flat and it’s <1.3:1 anyway. Good!
Now I’m waiting for real tests/comparison in open air, but i have to wait for better weather condition to go on my roof.
Concluding, the kit is highly suggested for OMs that have a minimum of manual skills and like to build antennas, but at the same time don’t have too much time for collecting material and want to start from a well tested configuration in order to have guarantee of success!
The kit is very complete and nothing else is necessary to build the antenna. The quality of the materials is very high and the price is very cheap compared to local shops.
Building instrunctions are also very detailed and easy to understand.
Everyone can customize the antenna and follow different solutions, but the suggestions, in my opinion, are the best way for good and quick results.
The only modification that I would consider, is to replace the steel screw and nut at the center of the dipole insulator (not visible in the previous pictures) with a nylon equivalent, since the screw is very near to the radiator parts (the center gap is only 10mm).
I didn’t have a 4mm nylon screw during the assembly, otherwise I would have changed it.
I hope this could help next OMs that want to build a twinband yagi and would consider a kit.