ATX Walkabout
As supplied by Yaesu, the FT-817 doesn't include an antenna for HF band operation. One of the earliest solutions to this problem was the ATX Walkabout antenna. This is sold by UK dealers Waters and Stanton PLC in the UK, and by MFJ in the US. The antenna is believed to be a Mizuho design, made under license for Waters and Stanton in Wales. It's still the best portable whip antenna for the 817, as well as being the least expensive.
The ATX is a base loaded whip. The base loading coil has taps for the principal amateur bands, 80m through 6m. Resonance is achieved by selecting the appropriate tap (in effect shorting out the lower portion of the loading coil) and then fine-tuning by extending or reducing the telescopic whip.
A disadvantage of the ATX design is that the WARC bands don't have their own dedicated taps. Instead, they are tuned by selecting the next lower band and reducing the length of the whip. This results in a whip length of about 18 inches on 30m, which is probably not very efficient. I would be interested to know if anyone has made a contact using this antenna on this band.
The ATX Walkabout can also be used on 2m. The instruction sheet states that it makes a 'reasonable' 5/8 wave on 2m. I think it is more than reasonable. I found that it gave 2 S-meter bars gain over a quarter wave, which is pretty impressive!
The original ATX Walkabout normally had a BNC plug for mounting on the front-panel socket of the 817. This version is still available, but the front-panel BNC isn't designed to take the strain, and more than one user has had the center pin of the plug break off inside, requiring an expensive non-warranty repair.
There is also a version with a right-angled PL-259 plug to fit the rear antenna socket. This is a much better bet, my only quibble being that when installed the antenna leans a little to one side, as it uses a standard PL-259 elbow connector and the 'teeth' aren't oriented to allow the whip to stand up straight.
The latest Mark II version of the ATX Walkabout apparently has a 3/8" screw connector and a set of adapters that allow it to be converted to an inline BNC, inline PL-259 or right-angled PL-259 fitting.
Counterpoises
To work effectively and present a good match to the transceiver, the ATX Walkabout needs to be used with a counterpoise wire cut to an appropriate length for each band. I didn't find the lengths suggested on the sheet supplied with the antenna to work very well. I determined my own counterpoise lengths for most of the bands covered by the ATX, and these are detailed in the table below. These lengths have been tried by some other ATX users and seem to work well.
| Band | Length | Whip Length [1] | Best SWR |
|---|---|---|---|
| 40m | See [2] | 9 sections + 2" | 1.1:1 |
| 20m | 17'8" (538cm) | 9 sections + 1" | 1.6:1 |
| 17m | 14'7" (444cm) | 4 sections + 1 3/4" | 1.1:1 |
| 15m | 12'3" (373cm) | 8 sections + 2 1/4" | 1.1:1 |
| 12m | 9'8" (295cm) | 6 fully extended sections | 1.4:1 |
| 10m | 7'11" (241cm) | 9 fully extended sections + 3" | 1.3:1 |
| 6m | 3'11" (120cm) | 7 fully extended sections + 3" | 1.3:1 |
| 2m | no c/p | 8 fully extended sections | 1.2:1 |
Notes:
- Extended sections are counted from the bottom
- 40m counterpoise comprises 36ft of wire. Approx a third of this starting from the end is coiled (3" dia) adding or removing turns until minimum SWR is achieved.
- Wire is 55/0.1mm extra-flexible PVC jacketed (Maplin code RB09K)
- Counterpoises should be laid out straight as far as possible and away from metal objects. Bends, and proximity with metal objects, will detune them, and it may not be possible to compensate by adjusting the whip.
I didn't bother with 30m due to my feeling that the ATX would be too inefficient on this band anyway. I didn't bother with 80m for much the same reason.
A tape measure counterpoise
After I had made the wire counterpoises, I discovered that a lockable steel tape measure makes a convenient counterpoise for the ATX antenna on the higher bands, with built-in calibration marks and a retractable case.
You can buy suitable tape measures for around £5 ($10) in hardware stores. I bought a 7.5m tape measure, but as you can see, a 5m tape measure would have been long enough. I also bought a large alligator clip such as is used to clip the charging leads to car battery terminals in a battery charger. I drilled the end of the steel tape and bolted the alligator clip to it. The clip allows the tape counterpoise to be firmly attached to the PL-259 elbow used to mount the ATX to the rear of the FT-817, or alternatively to the "legs" at the bottom of the 817 itself.
Here are the measurements I found:
| Band | Freq | Whip Setting | Calibration | SWR |
|---|---|---|---|---|
| 20m | 14.2 | Fully extended | 480cm | 1.1:1 |
| 17m | 18.1 | 5 sections | 390cm | 1.6:1 |
| 15m | 21.2 | Fully extended | 360cm | 1.1:1 |
| 12m | 24.9 | 6 sections | 330cm | 1.1:1 |
| 10m | 28.5 | Fully extended | 140cm | 1.1:1 |
This tape measure counterpoise should work with any whip antenna that requires a counterpoise.
A tripod for the ATX
Although the ATX Walkabout antenna with BNC socket can be attached directly to the FT-817, it is more convenient (and definitely safer for the radio) to use it on its own lightweight stand. This allows the radio to be tilted to a convenient position for operation. It also allows the antenna to be used with my Elecraft K2, whose rear-mounted BNC sockets aren't suitable for direct mounting of the antenna.
I made a tripod using a table-top microphone stand, a copper plumbing coupler and various other bits and pieces from my junk box.
Using a flat file take off some of the screw threads on the top section of the table-top mic stand. The 15mm copper plumbing coupler can then be persuaded to fit on to it, with the aid of a mallet. Drill a hole in the side of the coupler. The co-axial feeder will pass through here. If you have a very small rubber grommet in the junk box, fit it.
The BNC socket is fitted to a steel washer and the RG174 cable is attached. Feed the cable through the hole in the coupler, and fix the socket assembly to the top of the coupler using a strong epoxy adhesive such as Araldite.
A coaxial choke is made by forming a coil of about 6 turns of cable, about 4" in diameter, close to the stand. The cable itself can be any convenient length, but obviously no longer than necessary due to the relatively lossy nature of RG174. Attach a BNC plug to the other end.
A small alligator clip is soldered to the top of the steel washer. It is used for the convenient attachment of counterpoises.
You will find this tripod stand ideal for indoor use of the ATX. For outdoor use you will need to place rocks against it to prevent it blowing over in the wind.
