I own a Jayco 23 foot camp trailer. I often go to RV camp grounds and I like to get in some hamming away from my home QTH. I've always been concerned about hazards to the other campers such as guy wires or wire antennas that have fallen down. As a result I been searching for alternatives that minimize these potential hazards. Some of my RV'ing friends use Buddy Poles others use mobile whips mounted on their RV's. The most common method it to permanently mount a mobile mount on the ladder used to access the top of the RV. Once their camp is set up they attach the mobile whip and feed line to the mount.
My trailer does not have a ladder. So my solution was to put a second spare tire mount (available at Harbor Freight) on the rear bumper of the trailer. I "rigged up" a couple of eye bolts and a locking hitch pin to hold a mast. A short piece of PVC protects the fiberglass from damage when it moves because of wind. See Picture 1 and 2 below. I prefer a Jackite 30 foot fiber glass telescoping pole available at jackite.com or amazon.com. I use a Jackite 20 pole strapped to the gas bottle cover in the front to hold the far end of the antenna. That way everything is over the trailer. These poles are not fishing poles with the very flexible top section. These poles are designed for wind socks and flags. The top section is not hollow tube but rather sturdy solid rod.
The antenna is 51 feet of #22 AWG stranded wire used in aircraft construction. This is just wire I had in the "junk garage". Yes my junk box is one side of a three car garage. The only thing I'd recommend on the wire is that you use something quite flexible. I pull the wire up to the top of the 30 foot pole on a halyard. The far end goes to the 20 foot pole to make an inverted L with the vertical leg 30 feet and the horizontal led 21 feet running downward at about 30 degrees. This downward angle is of little significance in the antenna's performance. I use a light chalk line type cord throughout. The horizontal leg does not reach the 20 foot pole so I use the same cord to make up the need length to reach the wire and then down to pole.
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| Picture 1 |
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| Picture 2 |
I wound a 9 turn unun on 2 1/2 inch PVC pipe with about 1/2 inch spacing. The wire is bare #14 AWG. I used hot glue strips at interval 1/4 the way around to hold the wire in place. See the Picture 3 below. I tapped the unun as shown in the table below.
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| Picture 3 |
UNUN Tap Data
Turns above | Turns below | Turns ratio | Impedance | Matches 50 Ohms
ground | the antenna | | ratio | to the following
| 1.75 | 7.25 |
| 4.14 | :1 | 17.16 | :1 |
| 858 |
| 2.00 | 7.00 |
| 3.50 | :1 | 12.25 | :1 |
| 612 |
| 2.25 | 6.75 |
| 3.00 | :1 | 9.00 | :1 |
| 450 |
| 3.00 | 6.00 |
| 2.00 | :1 | 4.00 | :1 |
| 200 |
| 3.50 | 5.50 |
| 1.57 | :1 | 2.47 | :1 |
| 123 |
| 4.00 | 5.00 |
| 1.25 | :1 | 1.56 | :1 |
| 78 |
| 4.50 | 4.50 |
| 1.00 | :1 | 1.00 | :1 |
| 50 |
I used four large mix 31 snap on ferrite beads distributed around a two turn 6 inch coil of the feed line about a foot away from the unun to suppress RF on the feed line getting into my RV. See Picture 4 below.
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Picture 4
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I ran this setup for nearly a month this summer while out and about with good results. I did not use that data because I felt it was better to use the Winter Field Day data. The Winter Field Day data is the same mode and power throughout. The resultant date will be a better representation of the antenna's performance and not a function of applied power or operating mode.
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| Antenna design model |
The grounding scheme is a closed loop around the perimeter of the trailer. It is a 68 foot long loop made of 2 inch wide aluminum/mylar tape. ("Mutual Industries 17774-25-2000 Polyethylene Underground Water Line Detectable Marking Tape, 1000' Length x 2" Width, Blue" available at Amazon, about $30 last I checked). This works like a non-resonant counterpoise or ground mat. It just provides capacitance to ground. That is the wires you see in the model labeled 4, 5, 6, and 7. I loop it around the trailer to keep people from tripping on it.
The "on the air" performance for the antenna is documented below with data from my Winter Field Day log. I was running 25 Watts on PSK31 for the entire time using battery power. The radio was my IC-7300. I used my LDG Z-11PRO tuner with 20 feet of RG8x feed line into the trailer. The tuner in the 7300 does not handle wide range of impedance presented by the antenna.*
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Winter Field Day Log Data
Call UTC Freq
Distance
------ ----- -----
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Begin 01/25/20
W7D 19:15 7.071
671.1
KN4FRG 19:43 14.070 1076.7
N5OAK 19:51 14.071
1092.9
W0ARC 19:56 14.070
1057.8
KC5LVW 20:02 14.070
1077.3
KD5ILA 20:10 14.070
1042.0
KI4ITI 20:30 14.071
1444.9
K9BY 20:52 14.070
1190.9
N4MZ 21:22 14.070
1541.8
N4ZC 21:25 14.071
1728.8
W5AWL 21:52 7.071
1014.0
KB9REV 22:04 7.071
1251.8
W7A 22:06 7.070
707.2
NV7AV 22:15 7.071
392.0
WA5WRL 22:27 7.071
1022.0
W0BLK 22:30 7.071
493.4
K7SI 22:46 7.072
285.9
W4CVY 22:56 7.071
1606.6
WB6AGE 22:58 7.071
662.0
K5LRK 23:02 7.071
1001.4
KC8QDP 23:09 7.071
1582.5
K5OQ 23:47 7.071
1133.6
N7YIQ 23:51 7.070
415.7
W0IZ 23:56 7.071
266.8
Begin 01/26/20
AD0ND 00:02 7.071
804.3
W7GBU 00:07 7.072
514.8
KD5ILA 00:16 7.070
1042.0
W9UUU 00:22 7.072
1301.1
W4GR 00:26 7.070
1603.4
KC3FL 00:31 7.071
1872.5
W3GQ 00:34 7.071
1719.7
NV1O 00:38 7.070
531.7
K6EI 00:44 7.071
589.8
WD6RAT 01:02 7.070
556.7
W7PIG 01:07 7.071
317.8
N4MZ 01:49 7.070
1541.8
W2OW 01:51 7.071
1851.3
K5IJ 01:53 7.071
1477.5
W2SO 02:01 7.071
1711.2
W8VVL 02:14 7.071
1453.9
W8VA 02:14 7.071
1576.5
KD9IPZ 02:31 7.070
1333.9
VA3TPS 02:56 7.071
1694.3
NT7H 03:26 3.581
673.0
W6ZE 03:40 3.581
596.0
NV7AV 03:42 3.581
392.0
K7KY 03:46 3.581
632.7
W5RRR 03:50 3.582
1242.8
WB6AGE 03:55 3.581
662.0
W7PIG 12:51 3.581
704.9
K7UVA 12:53 3.580
59.6
W5PDO 12:59 3.580
477.6
W9LRC 13:05 3.581
1248.8
KE8RV 13:07 3.580
1500.0
W4SHL 13:23 3.581
1480.6
KB9REV 13:28 3.581
1251.8
K1KRN 13:50 7.071
2020.5
VE3YRA 14:12 7.071
1660.1
K5LRW 14:39 7.072
660.1
K5WXV 15:06 7.071
1007.9
K7IRA 15:26 7.070
511.6
KE6SHL 15:40 7.071
507.5
Callsign, date, and time from my Winter Field Day Log
Distance from QRZ.com
Total QSOs 62
Distance
1041 miles average
2020.5 longest
59.6 shortest
73,
Keep On Ham'n
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* - High SWR has little to do with how well an antenna radiates RF. The losses experienced due to high SWR are losses in the feed line especially coaxial cable. The primary reason for keeping the SWR low is to keep the finals in the transmitter from overheating and being damaged. That is why I have kept my coax to 20 feet. And yes there are losses in the tuner due to adjusting for the miss match. I try to look to "on the air" performance when judging an antenna.
