Re: Preliminary results -- W8TEE/AC8GY Mag Loop Testing

Robert D. Bowers
 

A friend of mine reported very good results with one of the loop antennas sold by MFJ (40-6 coverage as I remember).  He liked it because of the noise problem - here it can be a huge issue (not unusual to have S9 noise at least a couple hours out of the day, and some days 20-40db over the whole day).  He got out fine - but the big difference is that he could hear others.  (I've been thinking about building a loop - because of the noise, but even more so because they're small and work without being high up - and this area IS bad for lightning (a couple of direct hits on the tower over the years and many strikes within a couple of hundred feet at most, only a few repairs needed in the shack due to very good grounding, a disconnect 'patch board', and careful layout).

This thread reminds me of what I was told about a person wanting to run 40m (I think it was for a contest, but for something 'special').  He made up a quicky dipole and just threw it across the tops of some bushes, a few feet off the ground.  He said it worked GREAT, so much so that a couple of other hams were going to try it.  You wouldn't think it would work so good, but he said he did really well with it.

Another story - there was a huge sinkhole that suddenly formed here in Florida.  A ham lived just outside of the danger zone, and reported differences in how his antennas operated as the water level (immediate water table) rose in the sinkhole.  (I don't remember if his setup worked better or worse - just that it changed.)

The thing is, every ham lives in a different situation... different factors that will strongly affect the performance of their antennas.  Good ground and conductive soil (moisture) vs dry desert and poor ground, you name it.  If one has an idea for an antenna, try it.  It might be just what is needed in that person's situation - and it's great fun trying.  That's part of learning the electronics/radio portion of Amateur Radio... so you can have ideas of how to work around issues you may encounter (like poor grounding).  That's just part of being a good op.

Bob

N4FBZ

On 6/9/19 10:14 AM, EI4GNB wrote:
I knocked up a 3-turn loop, with an old soviet era vac-cap, total length was 10m of copper tube, and it covered 160m thru' 30m and did work very well, although the bandwidth was so skinny on topband, it did not allow for use of the internal tuner in my rig, tuning slightly off the SSB frequency as auto-tuners do when using a carrier. It just weighed so much that it was impractical. Did manage trans-atlantic on FT8 on Topband using it, so not all bad.

Next i tried using LM400 coax instead of the copper in a single loop, with 2 favourite lengths in the kit and a much smaller Vac-Cap, and i can work 40m thru' 6m by swapping out the coax (basically a long patch lead) and doing a slight tweak to the vari cap. I housed everything in an ABS box with SO239 for the coax loop connected to the cap, and i mount it on a small fibreglass pole, strapping it to whatever is available with luggage/shipping straps when out & about. Sure beats end-feds or tryign to support a vertical or inverted V etc.

I feed all my loops with a ferrite ring BTW, just dangling on the coax loop opposite the cap which is in the ABS box the loop hangs from.

Sure, this ain't no 'Cloudburn 5000 XL-DX Superblast multi-element face-melter' of an antenna, but it punches WAY above it's weight, and if You get lucky, You may even catch something to eat with it.

Join BITX20@groups.io to automatically receive all group messages.