Saturday, April 27, 2019

WSPR - 40m, ZL5A Scott Base Antarctica

WSPR pulls out another surprise.

Adam Campbell / ZL5A from Scott Base Antartica:




Wednesday, April 17, 2019

Low Band DX - 4 - Vertical or Dipole?

Vertical or horizontal dipole? Excellent question, since I began my low band DX quest, I had assumed horizontal dipoles are NVIS or short hop only antennas, due to the effort required to elevate them 1/4 wave length or more above the ground.

A few days ago I started looking at phased verticals to make some gain, and had settled on a plan to build two 80/40m trapped verticals based on W8WWV - Hex Array - 80/40 Meter Vertical, spaced 33 feet apart - 1/8 wave on 80, 1/4 wave on 40, and setup phasing for 135 degree phase shift on 80, and 90 degree phase shift on 40 with the option to reverse the phase to switch directions.

While scouring the internet for information, I ran across Verticals: got two? by N4JTE. Ok I thought, Bob had success with this, then I took at look at Bob's QRZ page and discovered that Bob had discovered something even better, the same thing but horizontal!

A while ago I noticed something interesting when comparing radiation patterns for verticals and horizontal dipoles, on first glance one concludes vertical has all the power down low. But when I compared the actual gain figures at 10, 20 and 30 degrees elevation, the dipole, even when under 1/4 wave length high has more gain. I dismissed it at the time thinking, I must be overlooking something.

¯\_(ツ)_/¯

I started looking into this again and found:



Above from http://www.chem.hawaii.edu/uham/portant.html comparing antennas on 15m:
  • A very highly optimized vertical. It uses 16 elevated radials 28 inches off the ground.
  • Horizontal fan dipole (0.3 dB better than regular dipole) at 15 feet above ground, 15ft on 15m band is between 1/4 and 1/2 wave length.
What's eating the vertical's energy? That null up top should be pushing more out at a low angle.. Ground losses against the return currents to the base of the vertical? Only when verticals are over salt water does the low angle lobe "push" right out.

Now what? I'm not tearing down the inverted L just yet, but I'll be building an OCFD based on the ON4AA design with the center loading network for 80m. The balun I'll be using is Model 4116 - 4:1 Hybrid Balun 1.5 - 54MHz 3kW from Balun Designs LLC. I have built OCFDs before with Balun Designs OCF optimized baluns, and had pleasing results.

The fun part is I'll be-able to compare the two antennas for a while.

After taking a ZL-Special model in MMANA and dropping it down 1/8 to 1/4 wave length above ground, it suggests the gain will be several dB better than a vertical at low angles.

Ultimately I'd like build something similar to Bob's double whammy with 40 and 80m capability. From my location in the Pacific North West, orientating it for South West / North East it'll favor the Pacific, ZL/VK, Europe and Africa.

Another advantage of horizontal polarization = less local noise pickup, will the RDF exceed small receiving loops? Since I have a K9AY loop control box, I'll also be-able to compare these too.

Saturday, April 13, 2019

The 900MHz Club

After getting to know a new group in my area on the local N7OEP 70cm/6m linked system, there is occasional chatter about "the 900MHz club". Otherwise known as the 33 centimeter band.

ZL has an allocation from 921 to 928MHz, commercial two way radio gear is non existent that I know of except for the digital Tetra system around 860MHz. If there was analogue FM stuff around to modify, the commercial 25MHz repeater splits are too wide for the band. As far as I know, there is no activity on this band in ZL bar maybe a mad scientist or two frankensteining something together in their basement shacks. Those into things above 70cm start at 1296MHz and up into the microwave bands from there.

The US has 902 to 928MHz allocated, and here in Western Washington we have several 900MHz repeaters and some activity. Getting on 900MHz requires sourcing, reprogramming and sometimes making physical modifications to commercial 900MHz two-way radios.

I ordered two Motorola MCS 2000s from Used Radios, they shipped quickly, were well packaged and the two I got appear to be in good condition. The pair I got are the version 3 model that also make 35 Watts, 35 Watts at near microwave frequencies is rather respectable. Here in the Puget Sound area there are a couple of people happy to program the Motorola rigs. As for antenna's plenty of cellular stuff around that covers this band, cheap Yagi's can be found on e-bay and Amazon, or in the spirit of ham radio, make something! I ordered a couple 7 element 900MHz Yagis to try out at $16 each.

 

See Getting Started with 900Mhz (33cm) Ham Band by WA6AER for more info about whats what. The largest hurdle with this stuff is getting the radios programmed, either your self or by someone else.

Whats it like? Well like FM anywhere else except using a commercial Motorola radio gives things an industrial feel, no S meter, basic controls - on/off, volume, memory up/down, and a bunch of buttons that do nothing.



Time for something bigger and better than a folding table.

Monday, April 1, 2019

Low Band DX - 3 - Feed Line Routing and Grounding

As with any antenna project, appropriate cable routing and grounding is fairly important.

After reading some very educational and informative articles written by W8JI:


I realized I had some work to do, originally I had run my HF antenna feed line up the wall on the other side of the house, through the attic and down an internal wall into the shack. I had installed a ground rod at the far end of the feed line where the remote ATU was located when I had the Carolina Windom up - with that setup I had created my self a ground loop, a lightning protection problem and an electrical safety issue - House Ground Layouts has several diagrams of how to get this wrong, and how to get it right.

With that I routed my feed line around near the electrical service entrance burying it couple inches underground. At the service entrance I repurposed an old PrimeStar box I found in a pile of junk when we bought the house, along with an old PrimeStar Ku band dish thats now hanging up in the garage awaiting a project...

 

The copper strip I found at Lowe's in the plumbing section, this had the right sized holes for bulkhead N-type connectors, its actually lightly copper plated steel, I gave it a light coating of Jet-Lube SS-30 Pure Copper Anti-Seize to prevent rust and so the connectors would make a good electrical connection. The right angle N-type connectors are a little hard to find at a good price, HRO had them for about $6 each. The green wire runs about 3 feet over to the electrical service entrance grounding rods - I plan to upgrade this to something better such as a copper strip or heavy gauge wire later.

 

Feed lines run up the wall into a junction box I got from Lowe's, it allows for enough of a bend radius with LMR 400 to then go through the wall. The shack is on the upper level. A little work left to tidy things up nice.


On the inside I used a standard 4 port Keystone wall plate designed to take the Keystone snap-in connectors such as the RJ-45 bottom right - I plan to use that with CAT5 cable for K9AY loop control cable. The N-type bulk head connectors were just right with the o-ring and washer removed to allow the connector on the other side to screw up tight. Looks nice eh?!



Bonus pic, while I was walking around with the camera phone, a bumble bee had flown through the garage to the window and buzzed up the spider web. Bumble bee made a lucky escape and flew away back out the garage door as I mounted a rescue effort. You can see a large spider made an appearance in anticipation of some lunch, in-fact at least two of these guys live here, there was another one to the right just out of view!