cubical quad FM broadcast antenna

[Anonymous No.1637349]

looks like a tie fighter...
admissible power : 50 W PEP.
This is a prototype used to test wind/mechanical load. the balun/ feedpoint will go at the center because the center of gravity should go at the center of the boom. the driven element will be fed through a balanced twisted pair.
Will use PPR or PE tubing in the future (because PVC is lossy when it comes to radiowaves)
using 16mm piping now but will go 20mm for the boom
Final version will be tactical and for the 300~400 Mhz emergency services band, and will be 4 time smaller (area/weight) wise
Final version is visible on www.skynext.space

Some project pictures will follow.

[Anonymous No.1637353]

>>1637349
gain is 6dBi
this is a part of the reflector after a woodland camo paint job.
Doubled the number of fiberglass struts.

[Anonymous No.1637359]

>>1637349
tuning stub to alter the center frequency
made with PCB and brass screws

sorry for the too big first two images

[Anonymous No.1637360]

>>1637349
and finally, the balun... sloppy heat shrink coat job...

[Anonymous No.1637361]

>>1637349
all sizes metric

[Anonymous No.1637373]

>>1637349
Fascinating, OP. What does the cubical shape get you that a planar antenna doesn't? Is this a directional antenna like a moxon? Do you have one of those radiation pattern charts (pic related for it?

I'm a radio noob and antennas are mystical to me.

[Anonymous No.1637381]

Fantastic job OP. How does it load up? Does it radiate in the pattern you expected?

I would use this in a temporary installation, however, I'm a little worried about it's integrity with ice loading.

[Anonymous No.1637394]

>>1637373
I have only modeled it through NEC2 (an old school antenna modeler).
When it comes to SWR and other radio electrical characteristics, i'll have to wait for a decent VNA (Vector network analyzer) that i plan to buy. It will tell me if the antenna behaves well.
However, to make a real life test of antenna directivity and radiation pattern it's better to test it in an anechoic RF room. And that's another story (costs a lot to test)

Although it's possible to make a crude measurement with a two port VNA and plugging two dipoles for the first test at a specific distance (outside of the Fresnel zone) and then one dipole and the test antenna. (one antenna transmists and the other receives).
Then we compare the gain between two dipoles and one dipole and the test antenna.
Then it is also possible to move the dipole receiveing antenna in a circular pattern around the tested antenna and plot a radiation pattern.
Quite cumbersome to do it in freespace.

For higher frequencies it is a lot easier since the scale is way smaller.

FYI, all information i read comes from radio ham pdf books and articles. the antenna in itself is not so complicated. the balun (what makes currents symetrical in each segment of the wires) is the difficult part.

And yes of course it is a directional antenna.This two element antenna is equivalent to a Yagi with 3 elements (the vanilla TV style antenna).

It's gain is probably a bit less than 6dBi

I tested it with a Denon old school tuner with poor sensitivity and sometimes I hear well a broadcast station in the mountains 120 km range.

But as said before, the VNA test will at least tell me if the SWR (measure of the reflected power, which corresponds baiscally to the "matching" of the antenna to the expected impedance) is close to 1. (the theoretical perfect value) that I should measure at center frequency (designed for 95 Mhz).
If there is a mismatch, moving the tuning stub could help.

[Anonymous No.1637398]

>>1637381
thank you.
see :
>>1637394

When it comes to icing conditions and snow and wind I will have to wait for winter... I expect it to move quite a lot in strong winds.
That should not be a problem for UHF frequencies.
I will see what I get with polypropylene with thick walls, or ABS.
The fact is that I used standard electrical conduit PVC for the time being.
also 4mm diameter fiberglass struts (fishbone) are a little undersized.
Maybe I will need to use struts between the two elements because for now there is a bit of motion normal to the planes of the elements (in the boom direction).

[Anonymous No.1637645]

>>1637349
Why the cubical quad, OP.
They were first designed by missionary radio in Central America to combat the corona caused by high humidity.
Is humidity/corona a problem where you are?

[Anonymous No.1637653]

>>1637349
I think your fireplace flue could use some attention...

[Anonymous No.1637764]

>>1637645
Yes. the birthplace of the cubical quad is indeed Quito, Ecuador.
Although I did not know about the Corona discharge, I know that Cubicals have better performance than Yagi for the same number of elements, although they occupy a volume instead of a simple plane, but that's OK for small size antennas.
However, any use in woods or nature with branches may defeat the antenna if it gets stuck in vegetation. and that's an issue.
As stated, The final goal in the long road to making it into series production is to create a mobile (human laden) antenna.

The three specificities I know about loop antennas are :
-Less subject to current imbalances than a simple dipole. (although a balun is advised)
-Less subject to electromagnetic interference and noise
-Lower elevation in the radiation pattern (the angle to the terrain of maximum radiation) makes it a good antenna for local links.

Other than that, it's simple brand differentiation for a niche market as a goal.
Yagi's are too vanilla in comparison and so cheap in Chinese markets that it's virtually impossible to compete.

In the final design, I plan to use PPR tubing used for hula hoop instead of water/electrical conduits. see pic.

[Anonymous No.1637767]

>>1637653
The chimney draft is OK. but when the fire is started improperly some smoke escapes.

[Anonymous No.1637792]

you should link this to /hrg/ im sure they could give you some pointers.
but neat antenna, ive wanted to build one like this for awhile, but for 6m ham band

[Anonymous No.1639213]

>>1637764
The engineer got fed up with all his power going into a light show at the ends of his Yagi, so he set out to design an antenna with no end points.

[Anonymous No.1639242]

>>1637349
Anyone know how I can make an FM broadcaster DIY style? Those cheap Chinese car aux FM broadcasters are too weak

[Anonymous No.1639245]

>>1639242
Plenty of info online about that. The bongs have a lot online and its legal in NZ.

[Anonymous No.1639665]

>>1637349
Do you have any links to good sources to help a noob get started in learning this stuff.

[Anonymous No.1639746]

>>1639665
Go to /hrg/ ham radio general. It's a recurring thread full of anons who are knowledgeable in this field.