Wire
Inverted Vee Antenna
Yet another antenna that I've built and works well, giving good DX
results throughout the 11 metre band. This is just a simple dipole arrangement with
sloping elements which is easy to fit into most attics with an apex roof.
For this, I used a length of 18 S.W.G. (1.2mm) single core wire
(but anything will do) and cut to 5% less than those for a normal dipole. ie 143/F(Mhz).
However some trial & error is needed as this calculation varies for a number of
reasons ie. height above groung, wire size used and even influenced by nearby objects.
NOTE:- At this point may I suggest
cutting the wire length longer than is needed as it's alot easier to shorten the element
length than add bits on.
The feed to the antenna is a dream as the inverted Vee presents a
feed impeadance of 40-70Ohms, thus a good match for 50 Ohm (RG-58) coaxial cable. I used a
15 Amp terminal strip for the feed connections but a number of choices are available. See
below Fig.2 and Fig.3.
Once the connection to the antenna is made then I used drawing pins
to support the wire elements during testing. On a low power setting, check the S.W.R.
throughout the band (say 27.555 Mhz is the target). Remember If the S.W.R. is lower on the
lower frequencies then the antenna element will need shortening and visa versa. Below
(Fig.4) I've shown the testing I carried out when Installing the antenna.
The resultant length of the Inverted Vee antenna is
2.38m/element and S.W.R. 1.0:1 @ 27.5Mhz. Once all the trimming is done then the elements
can be secured to the rafters using what ever method you prefer. However to be honest I
left it with the drawing pin supports. Later I added a 1:1 balun at the feed point which
made the antenna work over a wider band ie. gave the antenna a larger bandwidth.
In summary: