2 band rectangular oblong loop antenna for 15m and 10m en

8/10/2019 2 Band Rectangular Oblong Loop Antenna for 15m and 10m En

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Rectangular loop antenna for 15m and 10m band.

About 3 years ago I installed a light constructed rectangular (oblong) loop antenna to take

advantages in the 10m band on the solar cycle top. A construction with bamboo 3,6 m high

and 1,80m wide.

This antenna was a great success compared to the easy construction and the cost that

summarized to less than 15 Euros.

So far i have achieved 231 DXXC countries, with a lot of new slots and about 10 new ones,

plus some rare IOTA islands and CQ contest awards.

Due to the steady decline of solar cycle 24 despite the second top that we experienced

recently, the 10m band is slowing down and is going to close in the next couple of years.

Therefore I decided to upgrade the construction with a steadier frame and a second band,

the 15m.

Although 12m is my favorite band I took in mind some comments about the interaction of the

loops in the vertical wires of the loop so I decided to go down one band and install and a

new loop for 15m.

In the above photo you can see some details for the new frame with the V shape of two 3m

each bamboo.


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The V part is fixed with a homemade iron support construction on a couple of old military

aluminum masts. The vertical bamboos are 2,40m long for the 15m loop and 1,80m for the

10m loop.

The frame is fixed around with a nautical cord to be steady. The 15m loop initially was very

close with cord but in rainy days I experienced an increase in the SWR and later a let the

wire free from the cord and I had no problem.

The two lower pieces of the cord are used to tight the antenna with the tower to keep it

steady from the wind.

First I put the 15m band loop, and trimmed the wire for best SWR. I operate for a couple of

weeks the loop alone with excellent results and reports from DX stations.

In the above picture you can see the V base and the aluminum surplus mast in more detail

with the 15m loop alone.

The down ends of the two small irons tubes that hold the bamboos are open to leave rain

water to flow.

The iron V construction will be replaced in the near future with an aluminum one to make the

frame lighter.


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Having some band experience from moisture in UHF connectors, I decided to make direct

connections with the loop wires and the coaxial.

I used a small piece of Plexiglas and I secured the coaxial with tire-ups. Two bolts fixed also

in the Plexiglas for connecting the loop wires.

I believe that this type of connection is much better than the use of UHF connectors.

The kit has a good sealing construction although is a cheap one costing 0,80 Euro and was

totally dry in all cases with heavy rain.

The kit was secured lightly on the mast with a plastic tape to avoid movements from the

wind.

In the lower part the hole for the RG-213 coaxial is greater than the coaxial to leave any

waters to flow down.

I made also an ugly balun with 3 turns in a 10cm tube for a line isolator for the RF that might

flow outside the coaxial to the shack.


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After then I installed the 10m loop and I trimmed again both loops for best SWR.

The lengths for the two loops are now 14,09m for 15m band and 10,85m for 10m band.

The length of the 10m band changed from when the antenna was alone in the air, and

increased from 10,79m to 10,85m. But I have to notice that I changed the type of the wire

from a 1,5 mm solid copper to 2,5mm multi stranded copper wire (36 pieces).


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In the above SWR charts I have to notice that the response of the 10m band loop become

more flat and more lower in the upper end near 29.000 Kc.

The 15m band loop has 1:1.5 or better along the whole band which is an excellent result.

In the above photo the antenna is looking to North America.

The antenna is looking to the 90 (270) most of the time capable to work Asia, Caribbean

and some how from Colombia to North America.

In some special cases for better results to NA the antenna is turning to 330 where there isalso an improvement with VKs and ZLs.

The operating experience until today is that the transmitting lobe is wide and there is no

need to turn the antenna every time a new DX appears in the air.

Of course in a special case like the Tromelin isl. DXpedtion the antenna is turned exactly to

160 to achieve a new one.

And that was done in 10m band !!!!.

2 band rectangular oblong loop antenna for 15m and 10m en

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