LW1DSE's home aerials (or antennas)

Electrically speaking, it is the mirror or negative of a dipole. Setting it horizontally, radiates vertically polarized waves, this is why at 144mts band where a large majority of hams prefeer or use verical polarization, I ser it horizontally. And although the elevation over ground is smaller than my colinear, the colleagues note small or no difference using one or other, during some time I used skeleton to communicate via repeaters in fone, and the colinear at packet radio wirh a BBS in Lanus (10km straight line) but several buildings and electric interference with Horacio LU7DQP (RIP last year). Digimodes usually demmand a better s/n ratio or severe slow down of the traffic will result.

Over it, the Slot Skeleton has high impedance at terminals, from here the need for 1/4 wave transformer or similar. But taking into account the 90° difference in what the radiation pattern issue, the lobes seem to be similar to a half wave dipole. In the book above cited, the author depicts it. In my opinion, the great advantage over other construction types, is the DC short circuit that it represents, being safer than a bazooka or open dipole, not accumulating static voltages sometimes being destructive for SS rigs, mainly its MOSFET first stage..
 
Thinking about to build a new 440MHz antenna, in some instances similar to the 144MHz above depicted.
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It may be a 1/4 wave for 440MHz with 4 radials, all in 3/8" or 10mm copper tubbing. The coax. magnetically coupled via a loop or link close to the bottom of the exited element. A stub couples 1/4 wave to another 1/2 w (may be several colinear elements). All DC grounded to get rid static and tin/lead soldered to ensure good conductivity. The L inverted that supports the entire set is a 2mm brass thinker, as used in the 144MHz unit. The M stains for magnetic coupling or mutual inductance as in the old good books was used.

Ideas or suggestions, welcomed.

Osvaldo LW1DSE.
 
I was wondering if maybe using a shunt feed rather than using a coupling loop might be easier?

Or were you aiming for 100% electrical isolation between the feeder and the antenna?

73, Mark...
 
Not 100% isolated, they share ground. The idea is: as a 1/4 line or multiples acts as a tuned circuit, and you can couple a tuned circuit to a small impedance coil (link as in old tube power amplifiers), then I can couple energy to and from the antenna via a link. Let's see if it's true my hypothesis.

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Holy smoke! That's one tough looking antenna!

As we say in the UK, a "belt and braces" job.

It will be interesting to see how the whole assembly tunes up. When I've built antennas for 433MHz in the past I've found that the dimensions and spacing of components can be very critical.

73, Mark...
 
Obviously, as frequency increases, difficult rises too. My idea is to pre-adjust the whole thing insede home, and when it is roughly calibrated, then test it ouside, at the mast. Let's see what happen.

I have two points to play with: size and location of the coupling link, and the height of the exited element. I suppose that with 3 degrees of freedom, a proper point of adjust I shall found.
 
The project is becaming viewable.
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Tomorrow, using a 200W giant solder iron, a good soldering to insure good conductivity. 1/8" brass screw are for mechanical mount, only.
 
Here is the process of soldering the 4 rods composing the ground plane:
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It still remains to complete the coupling loop. I designed the mounting in such a form that, if it doesn't work, I can return to the classic Gamma Match.

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The 200W heavy solder iron, made in China, but plastic wire replaced with another impossible to melt. A switch added for more comfortable opeation.
 
I feel happy. With the antenna project fixed only at my workbench, inside home and at 1.5m far from me, I could trigger three repeaters, not too far not too close to me (Quilmes, Bernal and Lomas de Zamora) and mantain a decent QSO with some gentlemen, alrhough it is roughly calibrated, SWR is a bit high and (as said) not outdoors yet. I have a video, let's see If I can upload it.
 
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First test of the antenna outdoor, at the sunday morning. The behavior is irregular, reflected power (not SWR or ROE) has several peaks and valleys inside the 420~440 MHz band, what makes me believe, the coupling loop (link) may be resonant in this range, and coupling is unstable as freq. varies, like two hardly coupled tanks.

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I uploaded a pic of the aerial to the Gemini AI (above), and also "tell me" the loop is too large, surprisingly it could understand with good presicion, what I am trying to make. So, don't discard Gemini as a possible asistant.

Next steep is to reduce the length of the coupling wire.

News soon.
 
More pics of my Frankenstein.

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The project continues, although its performance is far from I wanted for it. As Murphy said: "anything that can go wrong, will go wrong". But I will give it some more tryies
 
Update: As I can't reduce the ROE (SWR), I temporarily migrated the coupling to the commonest gamma match, and I found that the radiator is too short, estimated 2cm below the optimal. So I need to cut another copper tube of 9.5mm ~ 3/8" and 190mm long. But in any way, it seems that my idea of coupling inductivelly to the antenna is a failure. Let's give it some more time to investigate.
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For a coupling loop on 70cm you don't want to go much greater than about 2cm circumference. At a guess (looking at your photographs and using the RF connector as a guide to the dimensions), your original coupling loop does not look far off being a quarter wave in length, so the phase shift will be around 90degs. So, with one end grounded to the collar of the connector the other end (that's connected to the connector inner) will exhibit a high impedance (as much as a few thousand Ohms possibly), which would explain the matching problem you are experiencing.

73, Mark...
 
Thank you for the advice. It's my first attemp in UHF and surely I will make myriads of errors and mistakes. The important thing is to learn from errors and don't repeat them ;-)
 
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