Intro

Warning: If you intend not to use a preamp then beware that the QFH will be a dead short, if your receiver outputs 12volts DC then you may need to disable the 12 volt output either via switch or some other means.

Listed below are the tools and equipment I would suggest you prepare before attempting to start making the QFH.

First off have you got the QFH calculation Software and RIG journal issue 53? if not then you may find the following guide hard going, so here we go.

I will start at the end and then go to the beginning.

At this point you will probably have seen pictures of the PHQFH, this version is made from 15mm (1/2 inch) copper tube, their has been suggestions made that perhaps a model made from 22mm (7/8 inch) copper tube should be more suited to the centre  resonant frequency of 137.50, but I would need prove that it would perform better than the 15mm version, lets face it, it can be quite a chore bending 15mm so unless you are another Mr universe or you are prepared to anneal the tube I would stick to the 15mm.

Note from Ruud Jansen:

The diameter of the copper pipe has nothing to do with the
resonance-frequency of the antenna.  This diameter changes only a little bit
the res.freq , but more important, it change the impedance of the antenna. We
have made  many loops with different diameter and , by example a 8 mm
diameter is about 21 ohm and a 15 mm can be 30 ohm. Our results , how and
why will be published in the next RIG.

with regards :
ruud jansen PA0ROJ
chairman of the dutch workgroup KUNSTMANEN.

My original QFH was made from 10mm copper tubing only because I had some left over from my caravan renovations, but this was false economy, the elbows and Tee etc cost more than the total materials in the 15mm (1/2 inch) job, the 10mm (3/8 inch) version I tested in the loft and immediately noticed a huge improvement from my crossed dipole, over a period of about 2 weeks testing I was convinced that this design was almost perfect except for the odd null hear and there.

I then checked all the calculations, made some slight changes to the dimensions of both loops and balun, I had previously tried various types of balun and decided to stick with the trifilar.

I then made the 15mm (1/2 inch) version and installed it on my chimney stack about 45 feet from ground level, this extended my horizon considerably in all directions, I was then receiving clear signals from elevations down to 0 degrees from the south but noise appearing in the north earlier than I would have expected, I then noticed that the QFH was leaning Slightly to the south, I then wondered if the QFH was directional if so then it was back to the drawing board, I tried tilting the QFH north and checked the results, the south part of the pass increased in noise and the north part became clear.

This result was not what I had expected, so up with the ladders again, checked all the dimensions everything appeared to be correct, this phenomena perplexed me for a considerable time, so I decided to make changes to the loop dimensions again, I then got to Mark 5 and repeated the tilt test, this time I found that tilting the QFH made no difference, so I finally installed it vertical and then eureka.

The other experiments I carried out were using different types of cable, I found in my case that 17 metres (18.6 yard) of RG 059 straight from the QFH connecting block (no preamp) directly into my receiver gave the best results.

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