2016-07-14

4m, 6m and 10m Combi Antenna.

In a Google search I just found an interesting antenna concept for simple antenna capable of running 4, 6 and 10m.

The antenna is essentially a 10m dipole (can be horizontal or vertical) fed by two lengths of twin-lead cable in series, (from the antenna feed point to the coax) 86cm 450ohm and 295cm 300ohm, fed directly (or via a 1:1 balun) into a 50ohm coax cable. The antenna in itself is 2 pieces of wire, each 258cm long (essentially a 10m dipole antenna). The antenna is a relative of the G5RV type, though not identical.

The gain on 10m is, of course 0dBd, on 6m the antenna probably has a gain of 1 - 1.5dBd, and on 4m it is an Extended double Zepp (2x5/8), and the expected gain is around 3dBd. Sounds to me like a neat compromise for a tri-band antenna.

New Antenna and Cable 6m/2m/70cm.

Yesterday I mounted my V-2000 vertical replacing the old Comet (GP-15, I think), and a new CFD400 cable.
The resonance frequencies :
- a bit low on 2m, but but clearly SWR below 1.4 in the whole band
- nice coverage of the whole 70cm band, less than 1.5 in the useable part of the band
- Decent coverage on 6m, the resonance was adjusted to 50.5 and the antenna is easily <2 in the high end, and <1.5 on essentially all frequencies I will use it for

This is now connected to my 70cm/2m FM rig, and tested on 6m FM. Everything works fine, and it is an improvement above my previous antenna system.

Future improvements of this antenna would be preamps near the antenna, though not in the mast, and possibly a power splitter at the outputs of the preamps, in order to use the antenna for reception on more receivers. The preamp system would then be after approx 8m cable and a triplexer. The preamps should be controlled per band, and that will take a while to design and construct, including some programming, sequencers, the preamps per se, and getting some useable coax relays.

Update : The cable is now connected to a MX62 diplexer, sending the 2m/70cm signals to the VHF/UHF rig, and the 6m signal to the IC7300.

This antenna, at the height it is, is better than the R6000 in its current position on the 6m band, so until the R6000 is raised to a higher position the V2000 will be my 6m antenna.

2016-07-07

4m and 6m Antennas

At the beginning of the sporadic E season I built a simple ground plane for 4 and 4m, just using a 6m fibre glass telescopic fishing pole and a bit of wire. The antenna works fairly well on 6 and less well on 4m, mostly due to its low height - the top of the antenna for 4m is only slightly over 5m above ground, so shaded by houses and trees.
The pole influenced the antenna considerably, and I was very happy to have my antenna analyzer when cutting it to the bands.
This antenna has worked about 40 countries on 6m, and 5 on 4m.
On 6m it operates a bit better than the R6000 at 3m height.

It was time for a better 4m antenna for local (FM) and a minimum amount of DX, mostly sporadic E. I decided to use a Sirio CX4 which is an end fed half wave antenna. The 10m half wave came down and the CX4 was raised to about 6m (feed point for the half wave about 7m. As expected this works much better than the low ground plane.
For working local stations in SSB, where most are running with horizontal antennas, I need to mount some kind of horizontal antenna myself. I am considering initially to male two dipoles or delta loops for operation in different directions, just to get it running. More elaborate antennas will have to come later.

Now, what to do about 6m ? I want to raise the feed point of the R-6000 to about 7.5m, and that should put the 6m part of the antenna a bit further from the trees around it, giving a better 6m (and 10m) range. On 6m some horizontal antenna is needed, and, again, I consider starting with 2 dipoles or delta loop antennas. A simple "V" shaped horizontal dipole could provide some degree of omnidirectional radiation, though.

For an omnidirectional antenna a "Squalo" (square halo), or a "Big Wheel" could work, or two "double quad"elements at 90 deg. could be fed in 90 deg phase difference, providing a modest gain.

I would like to generate some more gain on 4 and 6, and some kind of phased arrays for fixed favourite directions are in my thoughts. Older hams may be familiar with the "Lazy H" antenna which has a bi-directional gain of about 6dBd. This antenna can be fed with open line feeder and a tuner, making the same antenna suitable for both the 4 and 6m bands. There are other options, and they will be explored.

For now the 4m antenna is operational, and I am often QRV on 70.450MHz FM, and sometimes around 70.200 SSB or CW.