First some background information regarding reception of SSTV Images from the ISS (International Space Station). I use the SSTV Experiments to test different 2m Handheld Portable Antennas to see which antenna provides the clearest SSTV Images transmitted from the ISS. My test setup is simple. Baofeng UV82 HT Radio, Short CoAx Cable, Cellphone with Robot36 and a "homebrew" handheld portable antenna. No other equipment like a tri-pod, writing board, recorders etc. A KISS (keep it simple stupid) setup. No frills no fuzz!
I have tested a few antennas during past SSTV Experiments. Here are the list:
1. Homebrew Copper Pipe Upside Down 2 Element Quad Antenna. (I used this antenna to receive WX Images from satellites)
2. Homebrew 2m Quarter Wave Antenna.
3. Homebrew DK7ZB-Duoband-Dipole for 2m/70cm Antenna
4. Homebrew ZS2U 2 Element 2m Yagi Antenna ( Second best results thus far)
5. Homebrew 2 Element 2m Quad Antenna
6. Diamond X50 2m Antenna
7. Homebrew 2m Flower Pot Antenna
8. Homebrew 2m Dipole Antenna (Best results thus far)
For the purpose of this article we are going to build the 2m Dipole Antenna. (Best results) It is cheap and easy to build and out-performs all other antennas mentioned above. I am not going to go into the theoretical side of this antenna. I am sure you can find information on this dipole antenna using a search engine if you want more information iro 2m Dipole Antennas.
You will need:
Material:
1.2m x 20mm PVC Conduit Pipe
2 x T-Piece PVC Coupler
2 x 500mm x 16mm Aluminum Pipe
1 x 100 mm x 12mm Wooden Dowl
4 x 14mm x 4mm Self Tapping Screws
2 x 4m Electrical Lugs (Heavy Duty)
1 x 1.5m RG58CU CoAx Cable (2m if you going to wind the coax coil)
1 x PL259 Connector
1 x Ferrite Clamp (See images) or wind 8 turns of RG58Cu on a 25mm PVC Pipe (85 mm long)
6 x 15mm Cable Ties
30 mm Piece of Soldering Wire
2 x 13mm Plastic End Caps to cover aluminum pipe holes
Tools Needed:
Pipe Cutter or PVC Cutter. Hacksaw will also work.
Marker Pen
Round File
Measuring Tape
Screw Drivers (Flat + Star)
Glue Epoxy
Pliers
Soldering Iron
Lug Crimping Tool
PVC Cement (optional)
Insulation Tape
Silicon Sealant
Test Equipment:
VHF SWR Meter
NanoVNA (Optional)
VHF Radio (HT or Mobile)
Coax Patch Leads
Mast (Non conductive)
Coax feed line cable 5 - 10m RG58CU 50 ohm
Power Supply for Radio
Constructing the Antenna:
Construction is straight forward. The attached images will assist you in constructing the antenna. I might just mention that you need to cut two 20mm PVC pieces (each 25mm long) of pipe to fit into the top openings of the T-Connector. You might glue them into place with PVC cement. The 16mm aluminum pipe will now fit into the T-Piece. But before you glue anything first use the round file and file the inside of the T-Piece so that the 16mm aluminum will go in all the way to the inspection hole. Leave the bottom connecting point of the T-Piece unchanged.
A word on the RF Coil (See image below) If you want to use the antenna for TX and RX, I would suggest that you add a Ferrite Clamp (See images) or wind 8 turns of RG58Cu on a 25mm PVC Pipe. (85 mm long) This will sent RF to the antenna and not down he coax line back to the radio.
Note: The length of the dipole element is 1000mm / 2 = 500mm (each element). Yes I know this is "unconventional" as normally this length is used for many Yagi antenna reflectors. In other words if you go by the book the two elements are to long. This is also reflected in the NanoVNA measurements. Be as it may the "proof is in the pudding" that this antenna work great on receiving SSTV images from the ISS. Even at this length one can still use the dipole for transmitting as the SWR is well within the limits.
Testing and Adjusting the Antenna:
After you assembled the antenna, fix it to a non conductive mast. Ensure that the matching cable and feeding cable is routed away from the driver elements and that you choose the selected polarity that you are going to operate with. Now ensure that you put the antenna and mast as high up as possible. Ensure that there are no other antennas, wires, metal objects close to the antenna to avoid interactivity between the antenna and objects. Once up in the air add your SWR meter between the antenna and radio that you going to use. Ensure that the SWR meter is set to the correct power level. We will first use low power to test. If the meter has a function to select between SWR and reflected POWER then select SWR. Switch on the power supply and the radio. Set the radio to low power if you have such an option. Now press the PTT while observing the SWR Meter. SWR will be reflected. I was lucky enough that I needed no tuning and pruning to get a good SWR. If you followed the exact measurements then you should also have a fairly low SWR. You can then switch the SWR meter to POWER and press the PTT again. The meter now reflect the output power for your radio at low power. If this is correct then you have a fully working antenna. You can also go to high power and use the same method to test the antenna. My high power and SWR was also spot-on and needed no tuning. If you have a NanoVNA now is the time to put it to good use. I use both test instruments.
Performance:
I tested the antenna during a real-time pass of the ISS in receiving SSTV Images. The antenna was held in the hand and the ISS was "followed" as it passed over my area. The antenna was not always free of any obstruction, like trees, buildings etc. Some passes would result in clear images being downloaded while others would have some reception interference visible. Performance was as good as expected in my area. Maybe next time I will go to a park that has no obstructions.
Images: (Click on images for larger view.)
Here is two SSTV Images I downloaded with this portable antenna holding it in my hand:
