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Tag: antenna

LZ1AQ Active Loop Antenna

After many years using an active loop antenna with the Cross Country Wireless Loop amplifier for my SDR, I upgraded to the LZ1AQ active loop amplifier AAC-1C.

I replaced the former single loop wire – made of stainless steel – with two parallel loops using AWG10 (2.6 mm) copper wire. The loop diameter is 70 cm and the distance between both loops is 44.5 mm.

clamps for amplifier box
end cap small
end cap large
loop holder
all parts mounted
LZ1AQ amplifier board

As a holder I use a 1600 x 35.5 mm PVC tube (marked as 32 mm UPVC pipe) and added a 710 x 21.5 mm PVC tube (marked as 15 mm UPVC pipe) to support the loop. All additional parts are 3D printed in PETG. Besides the end caps and loop holder the wires are additional supported using four spreaders.

As before, the loop is mounted horizontal outside the apartment window in the 17th floor. In connection with my SDR the usable frequency range is 20 kHz to 55 MHz.

3D printed parts (stl)Download

80/40/30 m Dipole

For the lower bands I am using a 40/80 m trap dipole. In order to become qrv on 30 m, I added a radiation coupled lambda/2 element for 30 m, using 10 cm spreader. After cutting the additional wire to the right length, the resonance on 30 m is exactly at 10.1 MHz. The additional element has no influence on the resonance for 40 and 80 m, but the impedance on 30 m is with 150 Ohm significant higher than 50 Ohm.

VSWR_30m
10.1 MHz Impedance (141 – j34) Ohm – VSWR 3

40m_VSWR
7.1 MHz Impedance (40 + j1) Ohm – VSWR 1.24

80m_VSWR
3.6 MHz Impedance (27 – j5) Ohm – VSWR 1.9

Linear Loaded Dipole for 20 m

As the propagation conditions getting worse for 15 m and 17 m, I extended my linear loaded dipole on both sides by 1.8 m in order to cover the 20 m band. SWR is ok without modification of the 1 : 4 transformation line.

Will see, how it works in the upcoming CQWW DX CW contest.

G5RV Measurements

After replacement of my 80/40 m trap dipole with the G5RV antenna, I made some measurements. The antenna has a height of 12 m at the center, and is hanging as an inverted V with both ends still 4 to 5 meter above ground. The symmetric feeder line is connected via a 1:1 balun to 12.9 m 50 Ohm coaxial cable.

Continue reading G5RV Measurements

Fiberglass Balcony Stealth Antenna for 40 m

In Singapore space is limited, and in our appartment it is difficult to setup any HF antenna. Our balcony is the only place where I have a space to mount something. Even there, officially nothing is allowed to extend out from the building.

I decided to setup a simple vertical, using a telescopic fiberglass pole, which I can pull out temporarly, when it is getting dark.  The pole has a total length of 10 m, approx. 1 m (the lowest segment) safely mounted to the balcony railing and sidewall.

Continue reading Fiberglass Balcony Stealth Antenna for 40 m

Linear loaded short dipole

For my amateur radio activities on the HF bands I only have a 3.6 m wide balcony available for antennas. After some study I decided to experiment with a shortened dipole for the 15 m band. The full size 21 MHz half wave dipole would require a span of approx 7 m, therefore I searched for a solution to shorten the full size length by 50 percent.

Finally I decided for a linear loaded dipole; the layout and resulting dimensions are shown below.

loaded-dipole

First measurements at the resonance frequency showed a low input impedance at the dipole’s feed point with values around 10 Ohm. The theoretical radiation resistance of a 2 x 1.6 m short dipole would be 10 Ohm, so it is an indication of low losses in the system. In order to match the antenna to the 50 Ohm of the transceiver, I use a quarter wave transmission line transformer consisting of two parallel connected 50 Ohm coaxial cables.

50ohms_12ohms

After fine tuning the length of the antenna wires, I achieved an SWR below 1.5 for the CW segment of the 15 m band.

2016-03-26-1

The antenna’s bandwidth is around 200 kHz; I could already work DX stations around the world.

dipole-feed balun-1-1

Dipole feed point and 1:1 balun