A while back I decided to run separate 2m and 70cms antennas rather than the DUAL two band one I had been using. This got me some increased performance plus the ability to put each on a different mast and spread the load between then. At the time I fell back on my rather ancient Wimo 16 element for 70cms, while I brought into use an I0JXX 8 element for 2m.
There is nothing fundamentally wrong with the Wimo other than it is rather lightly built. I had it available so I put it back into action. However, I admired the quality of construction of the I0JXX and its excellent performance on 144MHZ so I had a longer term plan to replace the Wimo with a 70cms version from I0JXX. Eventually I bought a 16 element from Aerials Parts of Colchester who supply I0JXX antennas in the UK. Progress was delayed by damage to my Achilles Tendon causing me a lot of pain when I tried to walk. Eventually I realised that there is no antenna gain without some pain.
At last I have managed to get the replacement done, no doubt at the cost of setting back my recovery from the ankle injury.
 |
| New I0JXX left, old Wimo right |
As can be seen from the photo above, this is really a maintenance job. Both antennas have 16 elements and both have 3m booms. They look that same from ground level, which is hardly surprising. I just wanted to install an antenna which did not twist in the strong winds we get here. The main difference is the feed arrangements. I am not setting out to improve on the claimed gain figures - they are identical.
If you do not live a short distance from cliffs overlooking the North Sea you might not need a stronger antenna like this. On the other hand the round anodised boom of the new antenna, plus the strong stainless steel fittings might appeal for use anywhere. Like the 2m antenna I already have, this new one uses a unique element fixing arrangement whereby the elements go through the boom and are fixed by plastic locking nuts either side. Also good for rigidity and strength.
Assembly instructions are clear. The instructions include the EZNEC+ plots and a set of suggested stacking distances.
 |
| EZNEC+ plots for 16JXX70 yagi |
The parts included an Allen Key ("Hex Key") which you need to tighten the bolt holding the driven element to the boom. The snag with this was that the Allen Key was the wrong size. Not a problem as I have a wide range of Allen Keys available. That was the only issue with assembly.
 |
| On the Tennamast at GM4FVM - 16el 70cm top, 28el 23cm middle, 5el 4m yagis. |
Obviously it is heavier than the rather flexible antenna it replaced. It was easy to build and install. On the day of installation was the NAC 432MHz contest and I worked 1 x SM and 2 x OZ. Next day was the RSGB UKAC 70cm FT8 contest and there I worked 4 x G, 2 x GM and 1 each GD and GI. Best DX so far (after two days) is to SE5R in JO58 at 862km. It seems to work. The SWR is 1:1.2 on 432.200MHz.
 |
| View with the mast lowered |
This is basically a modernisation with an almost like-for-like replacement. I now have a more robust 70cms antenna and hopefully one which should last for years to come.
So far so good.
73 Jim
GM4FVM
No comments:
Post a Comment