HF bands in the US    

Part of the USA frequency spectrum use as presented by ICOM


Amateur Radio


The Beginning


As a fast riser in this new hobby of mine, I got confused where to go from here. The beautifully colored frequency table made available by ICOM made it not easier to pick a choice. Of course as an Extra Class Ham and proud of my call sign KB9TTI,  I could pick any of the bottom line options of communication, but which one would be the one that would be doable with my experience?

Through the contacts I made when attending the BARC (Boulder Amateur Radio Club) meetings, I found a group of people who were eager to help and answer my questions as they came along. One couple stood out. Since they were retired, they could spend a lot of time enjoying and expanding their hobby. BARC Juniors at a communication sessionEllie (NQCX) and Rip (NVM) live in South Boulder in the shade of multiple antennas planted in  the garden, protected by their ever watchful dogs. Ellie is in charge of the BARC - Juniors. Rip on the other hand is a "Hands on Pro" who loves to spend part of the day in his workshop or office if he is not looking after the Boulder Repeater at the top of the  NCAR building.


Rip in his Ham Shack

Rip in his "Toy - Room" (only a small section is visible)

Another reliable help was Bob (WLMA) of Freedom Avionics at Jeffco Airport Colorado. Featuring an impressive antenna farm on top of the hangar was proof of his dedication to the amateur radio cause. Meeting him frequently to bring one or the other of our ailing radios or aviation pieces for repair, I always picked up some encouragement or advice  to take home. Getting stuck with interpreting my ICOM 706 manual, he got me back on the road again. Of course I had to see the IC 706 in his wife's car using a rear window mounted antenna for her VHF/UHF contacts (Mary  K8AYU).

Being more scholastically inclined I had to get the ARRL Antenna Book. You guessed right, the close to a 1000 pages did not make it easier to chose the antenna to build. At least I could see what not to go after, especially since I was in a time crunch and I did not want to have a half finished project before leaving again for Switzerland.

I decided to start with my project at our retreat in the mountains, south of Estes Park. There were trees around the house which could serve as masts to get the antenna wires off the ground and what was most important; no restrictions in setting up anything. The easiest antenna would be a dipole I could stretch out between trees close to the house and run the feed right through the wall to my little shack I installed at my office for the 2m/70cm antenna.

The following weeks I spent countless hours at the computer using the EZNEC program to find out what the various wire configurations would give and where the limitations were. One of my main concerns were the two mountains (13-14'000 ft) on either side of the N-S line. Would they shield my contacts to the East and West. Checking the Topo Maps, to my relief I found  that the peaks were between 15 to 20 degrees elevation, thus not too great an obstacle for HF.

Three band dipole

As I felt not yet ready to build multi wave band antennas with traps and tuning circuits I decided to try to run three wires of different length parallel all fed from the same center point. [##1] The trees however, were not far enough from the house to permit an 80m dipole. Testing various layouts I found that it did not help much to try to spread the wires in different ways to uncouple them. Running the SWR calculation I found the expected main resonance on the 40, 30, 20 meters and additional resonance on the 15m and 10m band confirmed. Adding any more dipole wires to get the 17m and 12m bands would distort the resonance of the system unnecessary and created additional resonances outside the amateur bands.

Radiation pattern moddeled with EZNEC program

SWR calculationThe radiation diagrams also confirmed that the maximum of the radiation would be higher than the 20 degrees elevation and thus go over the mountains to the east and west.




 After having made all the calculations and planning, it was time to build the antenna and find out whether it would work.

##1 see ARRL, "Hints & Kinks", chapter 8

Response and suggestions are appreciated to  HB9TTI@Gmail.com

This page was serviced last on  12. July 2008