In my search for a simple home brew antenna for 2/70 with some gain I have finally given up. My latest plan is to concentrate on 2 meter ( 70 cm is dead in this area any way) After doing a few measurements I have worked out I can fit a 1/2 wave over 1/2 wave in the attic ( stealth operation) but only if I bend the J-pole matching section at 90 degrees, Have any of you done this and did you find it really had no affect on the antenna ?
Thanks all
Brad
That sounds a lot like the Ringo Ranger from 1980
The original Zepplin (“Zepp”) antenna is often shown as a half wave horizontal wire (perhaps with a drag cone on the end to provide tension) and a quarter wave feeder running vertically up to the airship. (Although the initial patent showed a round balloon with a linear antenna hanging down, as it had no propulsion other than the wind, which would affect the antenna similarly.)
So, yes, you can do that, and you wouldn’t be the first one to have the matching section come off at a different angle.
The rest of the wiring, ducting, roofing, metal flashing, and stored junk in the attic will probably affect the antenna more than turning the matching stub. You may need to adjust the tap points (feedpoint and shorting bar) on the stub a bit to improve the match, but it should work.
A simple dual band antenna is the dual band flowerpot design by VK2ZOI (sk) at vk2zoi.com.
Cheap and easy to build, it works so much better than conventional antennas plugged into a HT that you may think it has gain, but it is the reference dipole, demonstrating how much loss all the other antennas have.
Highly recommended.
73 Andrew VK1DA/VK2DA
I can remember them in name but haven’t knowingly seen one ,I’ll have a look and see if I can find a picture of one !
I’m using a Flower pot antenna at the moment which in all fairness works quite well but as a I have a bit more height I thought I would try something with some gain. I have built a few Slim Jims and single element J-poles in the past which made me think of the collinear version. I have an approx height of 7 feet and of course with it being in the attic it will not need to be so mechanically well built.
Thanks for all you input I will put one together over the next week and give it a try.
Brad
May I add a couple of other issues to avoid trying to break the laws of Physics.
Stacking 2 Dipoles at the correct stacking distance only provides a maximum of 3dB of gain achieved by squeezing the elevation polar diagram.
In a co-linear the current in the upper dipole is less than that in the lower dipole which tilts the polar diagram upwards.
This is a photo of the aerial I use for 145Alive. It consits of 2 HB9CV’s, each with a gain of about 6 dB at the correct stacking distance, so an overall gain of about 9dB. They are fed through equal lengths of feeder from a 1/4 wave impedance matcher on the pole. Single handed, it is not an easy aerial to put in the sky.
I said to my self last time I did the 433alive event that I was going to sort out a better antenna set up with some sort of mast but still haven’t done anything other than a patch up. I will have to build a dual band antenna ( most likely a flower pot) and get something I can use as a mast in high winds. That way I can use the same setup for multiple other events. Are your HB9’s collapsible or do you build them up on site ?
Quoting myself here but I have a 2 meter repeater at 50 miles away which is fairly active that I can just about get into and hold a conversation ( with the flowerpot) but am told it would be difficult to hear me for a mobile station so I need a little more oof to do the job properly. I could just get a more powerful transceiver but I am always interested in what I can achieve with just 1 watt ! The other problem is as I at present only have one feeder ( it goes out through a gap in the window frame up the back of the house halfway up the roof and then into the attic via a sky light ) I have to use that for everything. ( note to self create a cable duct up into the attic for more cables)
The HB9CVs are commercial to a high standard. They are transported on my rucksack. Assembly on site involves lots of sticky tape and cable ties.
Where would we be without sticky tape and cable ties ?
I have a 2m Moxon beam made from flat aluminium stock that comes apart and fits in my carry-on bag on an airline. Longest piece is about 40cm.
If you are primarily interested in gain towards a particular repeater than a yagi in the attic may work better: pieces of wire stuck through holes in plastic water pipe is a simple and inexpensive construction method, especially in an attic where it is protected from the weather.
I have a wire 2m collinear array that I need to write up that hangs from a mast or tree branch and has additional gain over a flowerpot. (Its actually a version of the old AEA IsoPole.) I still have to take some actual measurements to see if the additional gain is actually worth the construction effort. But it probably is too tall for your attic, if 2 x 1/2 wavelength barely fits.
I’m using a standard bent-wire J-pole in my attic at the moment, which provides adequate local coverage. The attic area over the shack is not easily accessible, so I punched a hole in the ceiling inside a closet, put the antenna in a plastic pipe, and stuck it up through the insulation (after carefully measuring the height available). The pipe is clamped to the header over the door, so you can only see the antenna if you walk inside the closet, turn around and look up.
