10-element antenna on 70cm SV1BSX

The antenna is used by Mak SV1BSX on a satellite uplink (originally mainly for AO-40). It is characterized by acceptable dimensions (boom length 1,5 meters), simple construction and impedance 50 ohm, which allows direct connection of the power supply to the radiator.

Mak SV1BSX: for successful communication via AO-40 it is necessary to meet the condition of the fulfillment 150 up to 200W ERP. Due to the fact, that most commercially manufactured equipment has an output power in the range 15 up to 25W, we need an antenna with gain across 10 dBd to achieve the required ERP.

Based on knowledge from various home made constructions, the ON1DHT design appealed to me the most. The SV1BSX ten-element antenna is based on this design. In the following description, I supplemented with several findings and analyzes from the YagiMax program.

The antenna has a gain 13,59 dBi (11,5 dBd) and is relatively small, about 1.5m long.
Technical parameters 10 El UHF Yagi

• Profit 13.59 DBi (11.5 DBd)
• 26 DB F/B pomer
• 430-440 MHZ (SWR <1,5)
• SWR na 435 MHZ = 1:1
• Impedance: 50 Ohms
• Hor. Beam angle: 33°
• Vertical beam angle: 38°

 

The antenna is an ideal compromise between gain and size… to increase the pitch by 3 to 4 dB would need to at least double the boom length and increase the number of elements. The given profit is also suitable for portal operation. With this length, the location of the antenna in the car, for example, is just right.

Construction

The antenna is constructed on a boome 15 x 15mm. The dipole is an AlMg tube with a diameter of 8mm, all other elements with a diameter of 5mm. It is very important to follow all dimensions.

A bracket is required to attach the antenna to the mast. In my case, it is located behind the spotlight. Never, I repeat, never place it between the antenna elements. For this reason, the boom is a little longer - 148,5 cm. You can also use a bracket in the center of gravity of the antenna, but I have to be made of non-conductive material or constructed that way, so that the mast and bracket do not interfere with the antenna area.

Dipól

The dipole is isolated from the boom. A plastic box is suitable. I used a box from a factory TV antenna. All other elements are conductively connected to the boom. I made aluminum strips as handles and each element is additionally attached to the boom in the middle with a screw. The picture below will tell you more.

The second screw is used to fix the position of the element.

Bazooka

The antenna uses a bazooka method of symmetrization to connect a symmetrical dipole and an asymmetric coaxial cable. The tube is conductively connected to the boom by a metal clamp at the reflector.

The tube has a diameter of 10mm and its length is 15cm. The coaxial cable passes through the pipe and connects to the radiator. The tube diameter is suitable for thinner cables (RG-58, AirCel 7 a pod.). If you use a coarser cable, the diameter of the pipe increases, but its length does not change.

Translator's note: Some commercial antennas are also used in this method of balancing, eg F9FT. Two more ways of symmetrization are offered, namely attachment of a coaxial cable at a distance of lambda / 4 from the radiator to the boom or coaxial stub.

 

AO-40 uplink

I use this uplink antenna with vertical polarization on both the portable and home QTH. I have a Kenwood TR-9500 for portable operation, which gives after adjustment 15 up to 17W (original 10W). The cable from TCVR is relatively short, other 1.35m (3x number x k). With this configuration, I established a number of connections via the AO-40. ERP is asi 150W (15W from TCVR-a times 11,5 dB antenna gain minus 1 to 1,5 dB losses in connectors and coaxial cable).

k - shortening factor of coaxial cable

I use the same TCVR on my home QTH, but the coaxial cable is longer (4 to 5 dB loss). However, this way I could not meet the ERP condition for uplink. I solved this by placing a small UHF PA directly under the antenna. I reduced the power on the TX to 5W, which is enough to excite the PA to 20W. ERP is therefore 20W of PA times 11 dB antenna gain - over 200W ERP!

The antenna is suitable not only as a satellite uplink antenna, but thanks to its good features and large bandwidth it is suitable for any traffic in between 430 a 440 MHz.

Makis, SV1BSX
http://www.qsl.net/sv1bsx/