Currently looking for a antenna for chasing HF SOTA and WWFF activations. Domestic and DX. Mind you the distances involved with domestic activations would qualify for DX anywhere else in the world.
We are on 4 hectares (10 acres) out out town so not under the height or space restrictions most are use to.
So first thoughts are of gigantic towers holding multi element beams. Hmm a hams dream. Such instillations are not cheap.
What do I need ? Basically chasing DX. This appears to to be a activity that throwing a heap of money at will not solve. So yes beams and tall towers are a option but for now a modest full size wire antenna will be deployed.
Antenna are a compromise.
Currently have a 80m dipole and a MJF-969 tuner. The dipole is above the house. So apart from the length basically a poor configuration not taking advantage of the available space. The wire dipole works well. 40m on weekend is a case of waiting untill the portable stations are resolved then calling. 20m if you can hear them they can usually hear you. Noise takes me out on the receiving site. CW helps here.
The dipole is directional. A omni-directional antenna is desirable.
Being in the country we are away from the HF noise prevalent in todays environment so don’t have to deal with all that. Not ready for a beam antenna. I can setup directional wire antenna as desired. Most of my transmttion is whilst portable. Chase portable from home on weekends and listen at night when I can.
Portable activations have taught me that for a effective antenna there are a couple of basic points to consider;
- When propagation is poor it does not matter too much what you are using.
- The more wire you get up the better.
- The wire has to be resonate. (The 21m end fed for 20/40 breaks this rule but thats HF)
- Not to worry about the trees as they have little affect.
- Balun to match at feed point
Initial plans were to cover only up to 80m. However if your going to go to the trouble of running the wire then may as well go as big as you can.
Recently upgraded to advanced licence so now can access more bands. Current Band Plan – September 2015. A full size loop at the lowest band I can operate on seemed relevant. 160m loop will be harmonically related to 80,40,20,and 10. See radiation patterns for the loop.
No 30,15 or 6m support. A 60m loop would address that. 12 and 17m would be best addressed with dedicated device. One thing at a time.
A full size horizontal loop of 160m was selected.
Ok well done. Where to put it. Placement factors;
- Antenna not to be seen from the house.
- Actually from the deck
- Discrete feeding
- not visible
- not creating a hindrance for access
- transmission line under ground
Feeding the loop will be the interesting part. I intend to use coax to the feed point. The majority of articles describe a ladder line fed loop. Ladder line is involved in the matching process. I have a 450 feed wire antenna initially for JOTI using 100w and the MJF tuner. Basically connected to tuner using a 4:1 match. It was this antenna I used for my first SOTA activation. Still use when camping. This antenna is not resonate and the feed used as a part of the antenna. This antenna works but no better that the full size dipole.
Going forward of the house will involve negotiating the septic or being above the solar cells. Not desirable.
A position behind the house feed with coax underground was selected;
The loop will have a feed impedance of 125Ω so will use a 2.5:1 Balun to match to coax.
Quality low loss coax that will support VHF/UHF should a small directional antenna be desired in the future.
LDF4-50 1/2″ HELIAX Coaxial Cable was selected;
- 5.02dB/100M loss @ 500 MHz
- 1.17dB/100M loss @ 30 MHz
- Velocity Factor 88%
N connectors will be deployed.
The existing MJF-969 tuner will resolve any mismatches. The existing dipole will be taken down.
There are a lot of options put there. Even towers for free as long as you pull down and transport. I had already obtained 5 X 2m triangular sections. This was location from Ballarat so able to drive in and load into trailer to bring home. Initially seen as a tower of VHF antenna but seamed suitable to act as a base for a loop or two.
Layed 90mm storm pipe for coax. Ran 60m of 1/2″ Coaxial Cable through to the tower. Laid a concrete base.
4 sections of the tower are up bolted to the concrete base with three guys at 6m. It is square, the photo not.
This with the coax laid will give me 8m of height fed to the lounge.
Planning on running 170 meters of wire all up as want to be at the lower end of the bands. Proposed length should cover harmonic of the HF bands;
|Freq Mhz||Length Feet||Length Meters|
Measuring the length involved a new tape measure and marking every 10m until done. First run came up with a resonate loop of 1.65 Mhz. Too low. Took 10 meters out and ended up with the tighter but still too low as resonate at 1.750 Mhz;
|Freg Mhz||Length Feet||Length Meters|
There are still points where the wire is touching the trees. Not a big issue as insulated but don’t want the drag. I’ve broken the handle for the chain break so chainsaw is currently at the service centre having this replace and receiving w well earned service. Will address the remaining branches once back.
First response is extremely positive.
Comparing with 80m dipole with 160m loop and there is no computation. The loop is noticeably quieter and 2 to 3 ’S’ points better on receive. VK6 stations are S4 than can not be worked on the dipole.
The TS850 internal tuner addresses the main HF bands with no fuss. 30m is a challenge but 12 and 17m resolve Ok.
So far very happy. More to do to finish but thats all for this week.