Regular reports of my grabber activity and that of others, plus information on QRSS software, hardware and technique that comes my way

Friday, October 5, 2018

Antenna comparison on 160m using QRSS

My main antenna utilizes a 50 foot (15m) aluminum mast with a multiband inverted V at the top for 20 thru 10 meters.  On all bands below 20m the coax is connected to the mast, which is insulated from ground, and fed as a top loaded vertical.  The ground consists of sixteen 30 foot radials plus six more varying between 60 and 100 feet.  It works all the dx I want on all bands.

There are two problems.  Firstly, it's in a swamp which  is full of spiders, snakes, mosquitoes, etc plus saw palmettos and thorn vines which will lacerate arms and legs not protected by heavy clothing.  Except in our brief dry season there is standing water and boat boots are a necessity. Secondly, it is a heavy rig and takes all the strength I have to haul it up and I'm not getting any younger.

I designed a new antenna based on the one above which is smaller and much easier to manipulate and is located in the "civilized" part of my property which we call our yard and garden.  This antenna is based on a thirty foot mast and sports an inverted V for 40 thru 10 meters and tunes on 160/80m as a top-loaded vertical with just four 30 foot radials.  Figure 1 is a scale drawing of the two antennas.

Figure 1.  Comparison Antennas

I suspected the ground losses on 160m must be much higher than on the bigger antenna in the swamp and arranged a test to compare the two using QRSS.  Both WD4ELG in North Carolina and VE1VDM in Nova Scotia have been running grabbers on 160m which I took advantage of by sending my call on alternating 10 minute frames for each antenna.

Here's how the tests were performed.  I keyed my TS-480 using the program QRS written by ON7YD at a speed of 8 dot seconds resulting in a total message length of about 8 minutes.  The antennas were connected to the A and B ports of the 480 and switched by hand at the beginning of each ten minute frame.  Over a one hour period I recorded three frames for each antenna, cropped and placed them together as a photo collage, Figure 2a.  The Spectrum Lab grabber at WD4ELG has a color scale for estimating signal strength which goes from RED (max) Orance Yellow Green to Blue (min).  The color variations are difficult to see but it does appear that the old antenna has a bit more red than the new one, i.e., the older antenna is slightly better.  I also tried averaging by stacking the images using StarStax with the "averaging" option selected, Figure 2b.

Be careful when making such comparisons not to over saturate by adjusting the exposure and contrast lest the true photographic density is ruined.  Note that these images appear underexposed and a little difficult to read but that's necessary to access the true image densities.

A similar comparisons was made using the grabs at VE1VDM which indicated the same thing, that it's difficult to distinguish between the two antenna.

I was both amazed and pleased to see the new antenna works almost as well as the old one but perplexed as to how a much shorter mast with a far simpler ground can do so. You should be able to see for yourself that how difficult it is to distinguish between the two but beyond any doubt the new, smaller antenna is doing a great job.

My QTH is about 1000 feet from Pensacola Bay and located on the slope of an ancient marine terrace.  What I call my swamp was once an nearshore trough which has filled in with organic muck  resulting in poorly drained soil.  My yard just up slope from the swamp has a six inch veneer of rich soil over white sand from the once sandy beach.   I'm just guessing but it seems that the ground conductivity in my yard is much better than expected  Occasionally hurricanes push salt water up to the yard so there is a possibility that salt may still be in the sand and soil.  In addition my QTH is on a long, skinny peninsula and the presence of a salt water ground plane, though at a distance, may also help prevent the low angle "suck out" phenomena which plagues vertical polarization.


No comments:

Post a Comment