Category: Okategoriserade
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QFA #9 and #10 in Anechoic chamber
I got the chance to test the QFA in anechoic chamber through the radio club and with help of my old friend Mart Sakalov SM0ERR. Antennas used during test are The results below are raw measurements and not yet calibrated with reference measurements. Will do that later For some repetition on circular polarisation and antenna…
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Published QFA antenna
Now when it works (I hope) the antenna is published in printables.com: https://www.printables.com/model/759022-qfa-antenna-70cm-band
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What is wrong with my choke?
In the QFA Antenna project there are many unexplainable results. To be able to troubleshoot things independently we made parts as separate components so they could be checked one by one. That seemed like a good idea at least. But never checked the choke separately because it was so simple and should not introduce any…
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Updating QFA SimNEC model controls
Adding simulation controls While looking into the code i found it is not so difficult to add controls for left and right handed helix and also for standard and anti-standard feed. Plotting radiation pattern with updated model The polarisation direction is easier to see with some ground. The polarisation handedness in air is opposite to…
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Dielectric constant
Having wondered for a while what the relative permittivity of the filament used for printing the antennas really is. It is time to test. There could be different characteristics depending on what chemicals were used to colour the filament. Created 50x50x1 mm plates of black and white PLA Basic filament. Added copper foil on both…
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Fixing up the current balun
Updated antenna model adding current balun with measurements, this is now available in github on djuptank/quadrifilar. Unfortunately it is not possible to measure power output with NanoVna because output would be grounded while it should be balanced. Maybe with some transformer it would be possible, but then the transformer would interact instead. Here is an…
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New NanoVNA-F V2
Needed better accuracy on measurements and got myself a new VNA. It seems more stable than my €70 older nanoVNO and can go up to 3 GHz so we can make more advanced antennas. Case Found a nice case nanovna-f-v2-stand-and-storage by werner_rh. Added my callsign SA0PEJ to model and printed. It can be closed with protection of monitor.…
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Publishing and Calibrating QFA model
To make avalaible for more interested people I have now put 3D model (FreeCAD) and simulation model (SimNEC/SimSmith) in github: https://github.com/djuptank/quadrifilar. I had to clean up teh code a little now when everyone can see it. After the new release of SimSmith 2.1. It is possible to tune model with changing relative dielectric constant (relative…
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“Paused” QFA
Decided to pause the QFA antenna – instead I got almost possessed and think more if it than before. Troubles and possible experiments It seems there is more to learn before abandoning this project: with immediate success nothing is learned….
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QFA RG58 => RG223
Found out today that cable choice probably has caused the recent setbacks. Hypothesis: Antenna was coupling into badly isolated cable running through center of antenna. Causing spurious response. We seem to maybe be back on track replacing with double shielded RG223; results seems predictable. But unfortunately frequency calibration needs to be repeated with new choke.…