Rockloop Antenna @dl1gsj

A magnetic loop made just of wire?

Years ago I started experimenting on magnetic loops & Co; I like the idea of narrow resonant aerials. When I saw the rockloop I never believed it might work (Ohmic resistance of the wire). Nowadays, travelling around a lot, I was looking for some antennas fitting my luggage. Again I found W9SCH's rockloop.

rockloop sketch

Thoughts to the original design

If I interpreted the original design correctly, the rockloop is constructed of a radiator wire, a transformer and a tuning capacitor. The transformer, as implied in  G3YCC's description , seems to be made of a different (at least another) wire than the radiator. Following the calculations that can be done on magnetic loop antennas, one knows about the extremely low radiation resistance of these loops. This requires the total Ohmic resistances to be as low as possible. To gain the lowest possible Ohmic resistance, I decided to use a larger dimensioned toroid core to fit five windings of the radiator wire on it (no solder joints, lower losses).



 sketch w/ dimensions
The four sides should have a length of 80cm, this will enable you to resonate the antenna up to the 15m band. If there are needs for the higher bands one should go for shorter sides. The transformation ratio was suggested by W9SCH. The 5 windings on the secondary side will influence the overall inductance of the loop...


Everything is said already. Just have a look at the photograph. I have to admit, there certainly are better  ways to mount the BNC connector...


Tuning Capacitor

We are going QRP with this aerial anyhow. I found this one in a old BC-RX (my favourite source for these things). It helps if the capacitor has two identical sections. Feeding just the stators will on one hand leave the rotator and therefor the chassis w/o RF on the other it double the voltage rating. The solder joints should be as solid as possible (remember the resistance story). I used a 80W iron to solder the loop wire directly to the stators.

tuning capacitor

Overall View

Showing pictures, it might be reasonable to show the whole thing. What I found helped, so there ist a  shelf's backside steelcross used to give support for the bamboo rods. This will disappear soon... making place for some more cable ties. Please excuse the poor light quality on this one, was made on a business trip in the middle of the night.

rockloop photograph


The tuning range is huge.  I observe resonance between 5 and 22MHz.  Even though it tunes on the 40m band, I believe transmitting there might not make that much sense - radiation efficiency would not be that great. I used the lower range to listen to broadcast.
First QSO on 20m during this business trip (Germany) resulted in a report of 579 from Hungary using 2W PSK31 (w/ FT817). At this time the antenna was hanging on a wardrobe (indoors, as you expect). The room was located at the ground floor of a steelwork office building.

Some news on my rockloop

I went out for some shopping, and that's the result (well, not the Al-boom on the floor):

2009 purchase

These things can be turned into something useful for the rockloop. Up to now I had it hanging off stuff like curtain rails etc. This, however, is not a real solution, in particular since sometimes, it is really difficult to find a mounting point not too close to walls.
Thus, here's a very very cheap and easy solution. The sunshade stand cost me less than 4 Euros, the spider web broom was about 4 Euros.
Let's see what the mod is like. The broom itself can be easily separated from it's telescopic stick. Simply pull (carfully) on the steel bits. Twisting the stick slightely helps a lot. The result would be something like this:


The top plastic bit actually does all the trick for us. However, there was some material connecting both legs on the inside part, that needs to be cut off. This modified bit perfectly fits my loop wire. Like this:


Next step, insert the broomstick into the sunshade stand. I skipped shooting a photograph of that respective step...
In the sequence of events, the plastic bit will mysteriously find it's way back home into the business end of the broomstick. As such:

bit back home

And the final result, as set up in my garage:

rockloop on broomstick