Archive for the ‘antenna’ Category
Big wheel antennas
July 6th, 2015 | 
Author: 
Next winter I want to replace my hand rotated beams for 70cm and 2m with a big wheel stack for either 2m or 70cm. I was going to erect a 2m big wheel stack (of 2) but looking at the logs it may better to erect one for 70cm which is the more interesting band.
2 big wheels, suitably stacked, should give about 5dBd gain horizontal and need no turning. This is not far off the gain from my 5el yagi in the best direction. Quite often I work stations off the direction of maximum gain. For my kind of operation (mainly UKAC contests and beacon monitoring) I think a big wheel is well suited.
70cm big wheel stacks are a lot smaller than the 2m versions. The stacking distance is smaller too. Commercial big wheels are available from Wimo in Germany.
VHF NFD 2015
The 2015 annual VHF national field day is now officially finished. So what’s the news?
Firstly I managed so excellent DX from the comfort of my own shack.
DX you say?
Yep 3 countries
Wow(?)…well yes they were EI,GM and GW so not exactly a long way but DX none the less.
Uhh?
Well yes, if the bands are normally silent and there’s not a station to be heard then the end of the village is DX.
But if there’s a bit of activity as there was this weekend then its always nice to work a few stations in other countries. But what would be really nice is to hear this level of activity on the bands regularly, and there to be rag chewing alongside contesting.
The ‘official entry’ from Workington was camped up on Corney Fell. I arrived too late to help get set up due to domestic duties but the photo’s didn’t do the conditions justice. There was a good 30+ mph wind up there and that 2m antenna was flapping about a lot. Hence the extra guy .
The VHF bands are XYL friendly in my house as the antenna’s are smaller, can be overlooked (on occasion) and
don’t warrant the usual response of ‘What the hell is that doing there?’ and ‘ How long do you intend on keeping that thing there?’ The answer to both of these questions is to mumble a bit and pretend to be busy doing something important.
So here’s a plea. Don’t make me take down this antenna, or worse still turn it vertically for FM. I’d quite like to work stations regularly on VHF SSB or even CW. Remember to switch the rig on, look for IO84 square and break the silence. A response to one contester today on 70cms was ‘That woke me up, I’ve been calling for 2 hours solidly and you’re the first one today’ isn’t good.
Big wheel antenna
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| Big Wheel for 2m |
A good 2m antenna for horizontal polarisation is the big wheel. Quite a few beacons use these as they require no rotator and a couple of these stacked give about 5dBd gain horizontally. So, these would be ideal for fixed station use. They would suit me well for UKAC 2m contests and general 2m SSB/CW use. I know that my 3 el, hand rotated, beam has about the same gain. One big wheel alone is better than a halo, but two suitably phased would be better than a small beam.
2 Meter Portable Ground Plane Gizmo Antenna
Portable, Ground Plane for 2 Meters made with BNC antennas
that you can ‘take down’
Its a compact ground plane antenna for portable use!
2 Meter Ground Plane Portable Gizmo Antenna in Operation 2
This antenna is built on a 2 inch washer. Holes were drilled in the washer to accommodate 4 radials. The center hole for the BNC to BNC connector was already there, but had to be reamed out. This (male to male) connector is where the coax from the radio is attached on the bottom of the washer. It also serves to hold (the center radiator element)!
(Note: The radiator, in the center, needs to attach to a BNC MALE connector, the cable from the radio also needs a BNC MALE connector. I used a male to male adapter for this purpose. It didn’t fit tightly so I used an old bike inner tube to cut a small spacer for taking up the slack. I’d have used a metal washer for ‘fitting’ the adapter, but I had already make 3 trips to the hardware store, so I used what I had)
Gizmo Portable Antenna
without the cover
Center Post of BNC Connector for the Radials are Shorted to the Shell Side
I used BNC female connectors from, Digikey, a good source for components! The center post of this connector is shorted to the ‘shell side’ to provide a ground plane with all the radials!
The 24 inch antennas from China were purchased on Ebay! CHEAP! The 2 inch washer is from the local hardware store. Everything fits on this washer, a 2 inch space, but the center coax is tedious to attach with all the radials in place, especially if you have big fingers.
The Cap is from a spice bottle!
I live alone so it was not a problem! LOL
Spice Bottle Cover
I love to use things for which they were never intended! This spice bottle cap is a good example of this. At this point, I’m not sure if I’ll seal it to the top BNC antenna radiator element or not? If I seal it (with hot glue, maybe) , the cap becomes permanently attached to the radiator element, and would be difficult if not impossible to remove. The whole idea here is to use this antenna as an impromptu portable antenna!
2 Meter Ground Plane Portable Gizmo Antenna Hanging from a Taped Tie Wrap
A tie wrap is used to ‘hang’ the antenna. Its hanging from a hook on my porch at the condo. I put 50 watts into it to get a repeater 10 miles away. SWR was 1:1 This is a portable antenna! Its not meant to be a permanent one. If you have ever needed a 2 meter antenna that you can pull up into a tree with a string or rope, this is it! Hauling it up 40 or 50 feet on a rope will get you better results than at ground level.
There is a joke that says, have you ever seen a golfer with only 1 club? Ham radio antennas are in the same category as golf clubs. You just can’t have too many!
All the elements can be removed for easy storage and transport, (radials as well as the vertical element)! I’m sure some clever ham will come up with a suitable case for this entire assembly. If I had one of those nifty clear plastic shipping tubes, I’d store in that! I’ll be on the lookout for one!
160m indoor loft antenna
Some years ago G6ALB and I wanted a simple talkback link that we could use when co-operating on experiments. We were 3km apart with Andrew being in the next village. We immediately thought about simple AM rigs for topband (160m).
As I had no 160m antenna, I built the design linked here. This antenna works well with best WSPR spots being over 1000km.
We decided that topband was too noisy for our simple AM rigs for our intended purpose. The noise floor at both our locations is very high on 160m. I have since moved QTH but we are still thinking about this link. We are now 3.3km apart. Probably 6m would be a better choice as less noisy and we both have vertical antennas.
See https://sites.google.com/site/g3xbmqrp3/antennas/160m_loft_ant .
Microvert antennas and similar
It looks like the Microvert antenna may have originated in Japan? The Microvert is a very compact antenna. Some believe the coax is a major part of the radiating system. Having never tried this sort of antenna I am unable to comment. This was posted to the Microvert Yahoo group earlier:
Whether you believe it’s the coax radiating or not, this is still interesting:
The Super Rad Antenna (Induced Secondary Radiation Antenna)
There are other websites about SRA (secondary radiation antenna), but unfortunately all in Japanese. Its definetly a Japanese thing!
I have all the parts required here to make one of these. Whether you believe its the coax radiating or not the results will be interesting.
Rob
M0RZFPS. My old 10m/12m modified microvert gives a good SWR.
Something that’s been bothering me
For a little while I’ve been pondering a problem on, or rather mostly off.
My SOTAbeams SB270 is a 2m & 70cm antenna that used a fairly unique way of holding the antenna elements. There are a set of elements for 2m and a set for 70cm. Each element had a hollow nylon cap head screw with a knurled end that was screwed into the plastic antenna boom. Unfortunately Richard can’t supply these as spares.
My SB270 is useful for, well SOTA, and the occasional VHF contest but what is makes up for in portability it lacks in gain. So I’ve thought about making a single boom version that covers 6m, 2m and 7ocm. The idea seems reasonable but the crucial aspect of mounting the antenna elements is a sticking point. Here’s a brief design brief.
1. Doesn’t need tools to assemble in the field
2. Must stay in place once installed
3. Must be easy to replicate (Just in case anyone else wants a go). So no need for specialist fabrication skills.
4. Must keep with the ‘elements live in the tube when not in use’ principle, So no big bulky parts
I have used standard pipe clamps and they get knocked about and blown around in our strong winds. Stauff type clamps need tools so they’re out. Some 3D printed parts are available on thingiverse but they look like they are for permanent installations or don’t really float my boat.
So, here’s the plea. Any ideas other than the one below?
The current thinking is to use some thicker walled ABS pipe (like durapipe which is cheap and easily found) and some threaded inserts for the parasitic elements. Only feeding the driven element is making me think a bit. May need a cut out or permanent part which has feeder and (ugly) balun.
Thinking caps on!
