RayBeam Story by I4LEC - February 12, 2002
Who is mentally ready to enter a 40 Meter, or
an all bands Contest, sooner or later thought about a 40 Meter Yagi.
The reason about this dream is simple, the usual V shape or straightforward
wire dipole, which has proven to be a realible and decently working antenna
on a daily basis just could not do enough in a Contest.
Certainly, before stepping up to a Yagi other easier solutions might be also
a choice to try. As a matter of facts our 40 meter Contester Candidate, as a
first move probably managed to add a piece of wire to his existing V dipole
and once the total lenght of 43 meters had been reached, and the match obtained
by adding a 7.2 meters of 75 ohms coax as a quarterwave transformer, he turned
out to claim on the air he uses a 40M delta loop.
Sure he added a little gain and dropped some noise to his system, but nearly
sure he forgotten to move the feed point from the upper apex, therefore polarization
turned out to be horizontal, wave angle high, with a lot of 59 plus from the
nearby contries and practically zero enhancement with farther areas and DX signals.
Then he moved the feed point to one of the lower corners for a vertical polarization,
this allowed a much better situation, expecially with DX signals but still not
enough to get really into the mess with *muscles*.
Before ending up to something effective our candidate probably tried all other
kind of wire antennas.
The loop became a 1/2 wave sloper, suddenly modified into a lazy V to lower
the take off angle, but then F/B dropped drastically and he was forced to add
other 3 lazy vees.
All those wires added to the existing 80 and 160 meter slopers turned out to
interact with the 10/15/20 meter antennas.
At this point a decision was taken.....
After having cleard out all 40M wires, a commercial trap rotary dipole, placed
below the triband antenna seemed to be the right choice.
Yes being on a clear spot and being able to rotate, it gave an extra help, but
once in the real battle, was still tought to pull-out week W's at 7.200, as
well as keep the frequency, then another modification became necessary.
By buying a kit, our rotary dipole became quickly a nice short 2 element beam
and an old dream came true, but not the end of the story.
Prior to the next Test, our Candidate had time to try his 2 elements beam for 40M, JA's DS's and VK's were answering his CQ DX Calls quit regurarly with good signal reports, F/B did not seem to be better than 10 dB, but who cares pacific island were calling and braking a pile-up was not a problem, an other world from the multiple shape wire used in the past.
When the D day arrived, our Contester thought
to be ready and finally competitive, in fact while running simplex, things were
going pretty well but around 23:00 Z he thought to start working US, and being
in SSB mode its 2nd VFO moved quickly on 7.186 (140 KHz from the resonating
frequency).
Few CQ Calls listening on 7.186, but this frequency seemed to be already in
used by some one else, then he tuned up well over 7.200 and finally after few
calls, few loud W's went easy into his log but soon he had to struggle traying
to pull out the week ones from the QRM.
Simply his 2 element trapped yagi on less then 5 meter boom was badly detuned
while on 7.200 and its pattern even worst.
What to do next to correct the problem??, a full size 2 elements might be the
choice to increase the band width, but with a boom length between 1.5-1.7 wave
lenght the antenna required quite an heavvy structure for a 4.5 dBD gain and
no more then 12-13 dB F/B.
The answer came while talking to a Ja, he mentioned
its 2 ele HB9CV, which consists of a 2 elements phased on a 1/8 lambda boom
lenght (135ø out of phase).
The gain of this system is very similar to a 2 ele yagi, but with much better
F/B and overall pattern.
In order to reduce even more the boom lenght and make simpler the matching system
the so called RAIbeam seemed even better, in fact boom lenght is reduced to
0.1 wavelenght (4.3 meters) and the delay line is made by means of a standard
RG213, 50 ohms coax cut exactacly 4.3 meters.
This system allows a gaing even greater then a standard 2 element yagi 4.5 4.8
dBD but does not drop the F/B which is little over 20 dB.
Up to now I already built two dual bander using
the RAIbeam design, 12/17 interlaced and 10/15 also interlaced, from this experience
and the help of Antenna Optimizer, next project is going to be our answer to
the 40 meter matter.
Do not forget to have a look once in a while within the projec section of the
MCC WEB page, the project of the Super 40 meter RAIbeam might be already there.
73 Clay, I4LEC