Bob Sutton - ZL1RS

6m Station

 

The header photo shows the stacked G0KSC LFA Yagis previously used here for 6m. They were destroyed in a storm on 15 April 2013. Since 23 April 2013 until June 2014 I was using a 7 element Yagi on a 9.6m boom (own design). Between June and December 2014 I had another own design prototype 6 element Yagi for a stacked array under evaluation (future plan). It did not have maximum gain for the boomlength, but it did have a very clean pattern especially when stacked in an array. Since December 2014 I've been using a G0KSC 7 element 6m OWA Yagi on a 7.1m boom that does not have such high rear lobe suppression as my own-design Yagis. After these experiments I understand how beneficial a clean radiation pattern is for very weak signal 'work' ... even in this quiet countryside QTH.

The current 6m equipment line-up at ZL1RS is:
Icom IC-7600 with audio via USB to a laptop running ham radio software (WSJT, Spectrum Lab, etc)
Bencher Paddles for CW
HB 8877 amplifier



Home made GaAsFET preamp plugged into the RX ANT In-Out sockets on the rear of the 7600


The present 6m antenna as from Dec 2014 is a home made 7 element G0KSC OWA Yagi on a 7.1m long boom. This is the same antenna design that I built for Victor E51CG in 2012 and that he is presently using on 6m:



G0KSC 50MHz OWA Yagi mounted above the KT34 HF tri-bander at E51CG. The rag-tag bunch of hams are Dusko (ZL3WW), Victor (E51CG), and some other guy (ZL1RS).

I built this antenna again to verify the wide SWR bandwidth and to compare the effect of 5 or 6dB worse f/b ratio as indicated by the computer simulation when compared to the previous high f/b own-design Yagis I have had up at this QTH. The actual SWR curve of the G0KSC 6M7 OWA Yagi tracks the computer simulation very closely (see below). The f/b ratio in real life is about 22dB and I notice the difference with less rejection of a local noise source than the previous high f/b own-designs (their real life f/b was approx. 28 to 30dB). Despite this G0KSC OWA antenna being a very good one, I will return to using high f/b antenna designs according to the preference/requirement at this QTH.

Here is the computer simulation of the present 7 element G0KSC OWA Yagi on a 7.1m boom:





The actual SWR curve as measured in the shack with a SARK-110 antenna analyser:



As can be seen, the reality is almost the same as the simulated SWR curve shown above (just 50kHz difference). The observed radiation pattern is also very close.


Here is the previous 6 element Yagi on a 5.7m boom used from June 2014 until Dec 2014:



A home made, own-design 6 element Yagi. This antenna was especially designed to have exceptionally low side lobes (clean pattern) in an array. The clean radiation pattern seems to help RX performance judging by the signals received via EME. The clean pattern reduces local noise sources. We have some local noise even though we live in a country setting 15km from the nearest town ... I can hear the power lines that are 3km away running along the roads to the SE and NE. The Yagi's feedpoint impedance is 28 ohms and is matched by a 1/4 WL coax transformer and balun (a modified "DK7ZB match"). Special effort was made to get the physical antenna to replicate the computer design with a boom compensation factor determined for the particular mounting insulators used, and with dimensions made to within 1mm. The SWR 'curve' follows the computer model almost exactly and is essentially flat at 1:1 SWR from 50 to 50.3 MHz. The main feed line to the shack is 20 meters of LMR-400.


Here is the computer simulation of the previous own-design 6 element Yagi on a 5.7m boom:



The reality is almost the same in both the SWR curve and observed radiation pattern.


Here is the earlier own-design 7 element Yagi on a 9.6m boom used from April 2013 until June 2014:





Highly suppressed rear lobes. The reality was not quite as good (about 30dB f/b), but still very effective at reducing local noise off the back half of the antenna.


The earlier antenna system was:
A home made stack of two 6 element G0KSC LFA Yagis for 6m (the "stacking version"). I chose this antenna as it has very low side and back lobes when stacked to reduce pickup of any local noise sources. The two Yagis were phased together with 75 ohm CATV hardline with 3 ferrite cores at each feedpoint as a choke balun. The phasing lines were also tightly taped to the booms and support mast to further decouple the coax outer. There was only one connector in the whole transmission line system ... at the station end. All other joints were done by mechanical and solder means.


The wreckage after a wind storm on 15 April 2013

The small aluminium tower and scaffold tube rotating mast will eventually be replaced by the bigger galvanised tower that can be seen laying in the grass (this tower was holding the 2 element 80m Quad I had up at my old QTH). When installed, the tower will hold something a little bit bigger on 6m than the previous experimental antennas.

 

 

 

 

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