N4HAY / ZS6RSH

02 April 2013

DVB-T dongle 2m/70cm antenna deployment

Having successfully managed to get the RTL dongle working I was now on a mission to explore further what I could hear with a better antenna/s. I could clearly hear the commercial FM stations on the broadcast band with a 2 foot piece of wire. I also copied the weather forecast on AM from Lanseria airport just above the noise. What could I hear with a decent antenna system?
After some searching around on the SARL VHF/UHF forum I read about the J Poles manufactured by ZS6PVW om Pieter van Wyk in Pretoria. I contacted Pieter and he kindly send me some pictures of his antennas for review. Please see the pics below.
I travelled to Pieter's QTH in Pretoria on Good Friday March 30th and spent a very pleasant time. He showed me around his extensive VHF/UHF antenna farm. His being a ham family meant that it is necessary to deploy enough antennas for everyone! I could see that the installation quality and quality of the home brewed antennas are excellent. It was clear Pieter's profession as an expert welder certainly provide him with the tools and capability to build a truly wonderful radio antenna farm. He has an antenna for every polarization for 6m/2m/70cm. Pieter told me about a lightening surge that destroyed much of the electronics in his home. However none of his antenna installations were affected. Perhaps a testament to the extensive ground system installed. Each mast has a separate ground system installed.
I purchased a ZS6PVW 2m/70cm Dual Band J-Pole. Here are the details as provided by Pieter.
Serial Number: 046
Manufactured: October 2012 by ZS6PVW
SWR 2m. 144.350-1.45, 145.000-1.2, 145,575-1.0.
SWR 70cm 430.500-1.2, 431.500-1.35, 433.500-1.6, 435.500-1.4, 437.500-1.6, 439.500-1.95
I was not able to measure the SWR since I dont have an antenna analyzer that works at these frequencies.
I purchased a 3 meter pole and bracket from Builders Warehouse. I installed the bracket on the side of the wall and to the right of the door entrance to my radio operating position.
I was able to copy the Sandton Radio club bulletin on 2 meters although it was not full quieting. I also can see a strong signal on 145.800Mhz. I believe this is likely an APRS signal. I have found that by increasing the RF gain on the SDR that I can slightly improve the S/N ratio. The dongle itself seems to show about a -60db noise floor with most received signals about 15db above this noise floor. There is good opportunity to adjust the controls on SDR# and so I am still learning about the optimum settings.
I am also able to hear a number of Airband stations quite well and many other NFM signals that sound like taxi or security firms.
Even though the antenna is designed primarily for the 2m/2cm bands it seems to be able to function reasonably across the VHF/UHF bands. I have yet to hear a repeater on 70cm, however I suspect is a lack of activity on this band.
The antenna is up about 2.5 meters above the apartment roof top, however there are surrounding building structures and roofs which mean that this is not an ideal location.
From the point of view of having something to play with in order to gain experience with SDR this is a great and inexpensive set up. I believe the ZS6PVW antenna will withstand any weather that we are likely to experience at this QTH.