Verulam Amateur Radio Club

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Antenna Shootout 2020 - Roger (M0RBK)

Posted: 15 Jun 2020 11:51 AM PDT
http://www.verulam-arc.org.uk/posts/...0-roger-m0rbk/







The antenna consists of:




1:1 Balun




Lengths of copper brake pipe approximately 1m long pipe and secured into
grooves in a length of wood.




“Stingers� which can be moved to adjust the length and secured with grub
screws.








It is secured to the mast with a stainless steel clamp.










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Antenna Shootout 2020 - Peter (G4HSO)

Posted: 15 Jun 2020 11:42 AM PDT
http://www.verulam-arc.org.uk/posts/...0-peter-g4hso/



Years ago I bought a commercial but cheap HB9CV antenna for 6m. I think in
terms of dB per gram of beam aluminium, these antennas are top-notch and
great for /P. (I have had a lot of success with good DX with my 2m
version.)Â*




However, rushing a first activation (contest) a few weeks after purchase, I
didnt test the antenna at home but took the parts to a high spot which is
near to our field site and completed the construction.Â* TERRIBLEÂ*VSWR!!!Â* I
only managed one QSO.Â* I came home and put the antenna in the garage. this
was around 15 years ago.Â*




The VARC 6m antenna challenge has made me remove the dust and re-construct
the antenna.Â*








I set up my FT817 in the shack, selected the rear antenna input, power,
frequency etc. and tested the antenna in the garden.Â* TERRIBLE VSWR!!!!Â* I
re-made all the obvious joints and re-tested.Â* TERRIBLE VSWR.Â* Checked the
FT817 now showing the wrong antenna selected. Finger trouble??Â* Re-tested
and all PERFECT!!Â* Fault not found.








I did some CQ calls and used the G3VER/P remote (c/o Peter G0OIK TU) to RX
and found the antenna had the expected lobe pattern.




I called CQ a few times (CW 50.096MHz) but no reply.Â* However, I did hear
some pings of obvious meteor scatter propagation well into Europe.








So, I now have a working antenna!!Â*




Peter G4HSO

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Antenna Shootout 2020

Posted: 15 Jun 2020 10:20 AM PDT
http://www.verulam-arc.org.uk/posts/...shootout-2020/



Every year Verulam Amateur Radio Club holds an Antenna Shootout Contest.
The idea is to get as many club members as possible building their own
antennas and then competing against others to see whos antenna performs the
best.




Over the years we have had loads of really interesting submissions, from
massive quads to tin-foil and even a usable antenna made from a length of
wet string.




We havent been able to hold our regular meetings during the COVID-19
lockdown so we cant hold our competition in person like we normally would.
Instead, we have been encouraging our club members to build their antennas
at home and send us some pictures and results.




Normally our antenna shootouts have a theme, and this year is no
exception. Quite predictably, our theme for 2020 is lockdown which means
that entrants can only build their antennas from items they already have at
home or in their shack. We also decided that this would be a good
opportunity to benefit from the excellent DX operators have been seeing on
the 6-metre band so we stipulated that antennas needed to provide coverage
of 50 MHz (6 metres).




We will be posting photos and notes from our competition entrants below.
Thank you to all of of our members that took part in this annual
competition.




Norman (G8ATO) 6 metre Delta Loop




Peter (G3UHN) 6 metre Dipole




Peter (G4HSO) Revisiting and old HB9CV




Roger (M0RBK) Adjustable Dipole

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Antenna Shootout 2020 - Peter (G3UHN)

Posted: 15 Jun 2020 10:16 AM PDT
http://www.verulam-arc.org.uk/posts/...0-peter-g3uhn/



The VARC Lockdown Challenge was to make a 6m antenna from materials found
at the home QTH. No sneaking off to local suppliers or mail ordering! A
rummage through my garage found the following:




Plastic rectangular-section conduit, two telescopic Band 1 TV antennas,
SO239 socket, ‘U’ bolts and miscellaneous bits of wood. Unfortunately, no
useful lengths of aluminium rod or tubing.




‘Back of envelope’ calculations showed the feasibility of making a 50MHz
(and perhaps also a 70MHz) dipole. Not particularly high-tech but hopefully
a lightweight, portable, antenna might be a possibility.








Work began by strengthening the plastic conduit, by gluing-in a wooden
insert. Next, the antenna end fixings were drilled-out, rewired and
reassembled.








Nuts, washers & bolts were used to attach the telescopic antennas to each
end of the plastic conduit (ends A & B).




A centrally located SO239 socket was wired to the telescopic antennas. Glue
was applied to connecting wires inside the plastic conduit, to form a rigid
structure, and so reduce the possibility of random resonances.
















The antenna was adjusted for a calculated resonance of 50.150MHz (SSB
centre activity frequency) and supported on a wooden step ladder at a
height of 1.5 metres (0.25 wavelength) above ground. Although not an ideal
height it was thought important to carry out some resonance/ confidence
tests, before proceeding with further construction.








Each telescopic antenna plus conduit was set to a total length of 132cm.
Resonance was measured with an MFJ antenna analyser. Resonance occurred at
50.141MHz with an SWR of 1:1.3, Impedance of 41ohms and a Reactance of 8.
These interim results were considered sufficiently encouraging to proceed
with further construction. The impedance was expected to change with
antenna height and the SWR expected to fall.








Time for some carpentry to make an antenna centre fixing panel to attach
the dipole antenna to a roach pole, bamboo pole or telescopic aluminium
decorator’s pole. Some of the authors favourite ‘sky hooks’!




The fixing panel was designed to add strength to the plastic conduit and to
enable both horizontal and vertical polarization of the dipole. Note the 6
holes in the fixing panel for the ‘U’ bolts, which enable either horizontal
or vertical orientation of the antenna.








Finally, the conduit was attached to the centre fixing panel using bolts,
washers, nuts and glue. The plastic conduit back cover was secured with
screws only, allowing future access to wiring.




Into the garden where the completed antenna was clamped to a 3m bamboo pole
using 2 ‘U’ bolts and tested once again. The MFJ Analyser was connected via
a 3m length of 50 ohm coaxial cable, without the use of a balun.








As expected, at half a wavelength high on 6m, the SWR improved with height;
the small change in impedance was considered quite acceptable.




For 50MHz, the length of each dipole leg was finalised at 132cm (52ins).
SWR = 1 : 1.1




For 70MHz, the length of each dipole leg was finalised at 91cm (36ins).
SWR = 1 : 1.2




Time to find a good elevated location for the antenna and make some 50MHz
QSOs …….





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Antenna Shootout 2020 - Norman (G8ATO)

Posted: 15 Jun 2020 10:16 AM PDT
http://www.verulam-arc.org.uk/posts/...-norman-g8ato/



I’m entering the Verulam Amateur Radio Club aerial contest 2020. I’ve built
a Delta loop with bits stored at the back of the house.




Items used are plastic electrical conduit and drain pipe, coax cable and
wire. Wire length is approx 6 metres, the conduit is 2 metres long. The
matching coax is approx 1 metre 75 ohms (converts feed impedance (100 ohms)
to 50 ohms.




The support mast is 40 mm sink pipe. The measured match is 1: 1.7 VSWR at
50 MHz, falling to 1: 1 at 51 MHz.



G8ATOs Delta Loop




The picture below shows the matching coax tube and cover. Tests are
underway to see how well it works.



Matching Coax Tube and Cover






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