(ATU stay at home)
It’s been four years since the antenna tuner last came back home, but unfortunately my home still has the old SG-230 in action. Although it’s a reserve player, it hardly gets a chance to be used.
So today I’m going to make a companion (antenna) for the balcony of an apartment building, so that it can be used by local stations who can’t gather in the club room while staying at home.
Here are the materials.
Two 2m pieces of HIVP-13 (a high impact resistant version of VP-13) used for water pipes, and seven T-joints (tee joints). I will use this to make a spreader for a small loop (MSL) antenna.
Commercially available MSL antennas have a diameter of 850mmΦ, so I made the antenna about 600mm square to fit within this square.
Why HIVP-13? I simply wanted this inconspicuous color, but in some places it might be more noticeable than VP. Here I go.
Make a slit where the element will pass through. This time I’m using 2mmΦ aluminium wire, but it’s impossible to make a groove width of 2mm in one go. Use a Piranha saw to make two notches.
I attached crimp terminals to 2mm gardening aluminum wire and wound it 7 times. The side of the square was 60cm, the height was 30cm, and the length of the wound wire was about 19m.
It weighed 863g. Even V/U 2-band GPs weigh this much. It’s light enough that there won’t be any problems installing it on the balcony.
The feeding section looks like this. The mast is the same HIVP 16Φ. A hex bolt is inserted into the different diameter socket to make it detachable.
Though indoors, I’ll check the tuning frequency of the bare antenna with an antenna analyzer.
The result is 21MHz or so… A simple calculation based on the actual length of the antenna wire would put it at about 16MHz, but well…it’s like a coil.
I hear that half of this, around 10.9MHz and its odd multiples (32.7MHz, 54.5MHz….), it seems that these frequencies are harsh for antenna tuners. Well, will this be okay?
I connected it to a radio in this indoor condition and tested the tuning operation. The results were: 1.9MHz band = Unable to tune (SWR = ∞) All bands from 3.5 to 50MHz = Tuned (SWR = 1.0 to 1.2)
After carefully reading the instruction manual, I found that the AH-4 does not support 1.9MHz. It’s no wonder it can’t tune. So it seems to be fine for transmission. There doesn’t seem to be any problem with the tuner circuit.
Next, I set it up in the garden and compared it with a permanent antenna (6m loading vertical + ATU). I’ll try this with FT8, which allows for a quick comparison of numbers.
I decoded the signal several times and then averaged the decibel values obtained, except for one maximum and one minimum sample. Both receivers are IC-7100.
| Callsign | This Small Loop Ant. (dB) |
Existing vertical Ant. (dB) |
| 7MHz | decode 7～8 Stn | decode 9～10 Stn. |
| JH8*** | -3 | +2 |
| JN3*** | -14 | -16 |
| JP3*** | -3 | +4 |
| JA3*** | 0 | +8 |
| JA1*** | -15 | -8 |
| JF6*** | -5 | -2 |
| JH5*** | -13 | -5 |
| １４MHｚ | decode 4～5 Stn | decode 12～15 Stn. |
| RC0** | — | -15 |
| KG6*** | — | -15 |
| W4*** | -12 | +3 |
| N7** | -15 | -4 |
| K7** | -7 | -4 |
| AH6** | -15 | -3 |
| 18MHz | decode 2～3 Stn. | decode 5～6 Stn. |
| FK8** | -8 | +1 |
| HL** | -4 | +3 |
This MSL antenna is horizontally polarized, so it cannot be directly compared to a vertical antenna with vertical polarization, but considering the height above ground and the effects of buildings, I think it is quite usable.
As a test, I called a station on JH5 that was -13dB at 7MHz, and there was an immediate response and the return report was also -13dB.
All of my HF transceivers are now ICOM, so the AH-4 can be directly connected, but I made a simple controller so that it can be used with rigs made by other companies. (Source: “Apaman Ham Handbook” by Mr. Haraoka, JJ1VKL) I also deliberately did the above operation without a direct connection, and it worked well.
This completes the “homestay system” for the AH-4, which was removed from the roof of the club room due to the stay-at-home order.
First on IOTA expedition to the Pacific Ocean 20 years ago, second on the roof of the club room, and I plan to have this tuner used by one of the club members. That willl be his third life.