Having recently purchased a small Sprinter based RV I was in search of a compact but well performing antenna for my HF ham station. I prefer dipoles but recognized the popularity and simplicity of the vertical. Eagle 1's(tm) being all the rage these days are basically a vertical wire within a fiberglass support tube and a matching network. I wanted the option of supporting a dipole so opted for a heavier duty collapsible FG mast by MFJ. The model 1916 is 34' extended, 54" collapsed and weighs in at #7. Either a single wire or a length of coax is placed up inside the mast. A small current balun is placed at the top of the mast when using the dipole. No tuner is needed for the dipole as it is cut to a resonant length. I used an Icom AH-4 tuner to match the single wire vertical, as this gives me some frequency agility and provides the needed match to the 50 ohm coax transmission line. This mast at 34' is close to a quarter wavelength for the 40meter band, which is a good choice as it results in feed point resistance close to 50 ohms. 34' is also close to a half wavelength for 20 meters, which is a bad choice because of the high feed point resistance. Remember the vertical element is only half of the antenna system and a proper "counterpoise" is needed. 1/4 wavelength radials or perhaps a 30' aluminum air-stream trailer will do. My RV has a 23' steel frame, which the tuner ground is bonded to.
Auto stow: Eagle 1's and other telescoping mast's have a tendency to collapse while in use due to the release of the friction only locking sections. I solved this problem by drilling a small hole near the top of each section and inserting a SS pin made from some old SS rigging wire. To avoid any alignment issues I located each hole just below the bottom of the preceding higher section. The weight of the higher sections keeps the pins in place.
No holes! Well at least no visible holes were to be drilled in the RV, as I wanted to preserve the resale value of the RV. I elected to mount the mast on the back of the RV to reduce setup time and eliminate carrying "extra stuff", though in it's present form it is not a permanent mount and the mast is dismounted when moving. The antenna is mounted on the back of the RV, and the radio is placed forward so I used the Sprinter chassis member as a wiring conduit from front to back.
The lower mount is a flat aluminum plate bolted under the fiberglass body to a backing plate with additional support provided by a threaded rod to the chassis. There is a 2" bushing on the top of the plate that accepts the bottom of the fiberglass antenna pole.
The upper mount is something I made up to "self capture" the mast, as the RV roof is too high to reach without a ladder. The dipole prevented me from using a simple hole in a plate. The mount is made of 1/4" lexan and an aluminum plate. The shape of the aluminum plate is such that it "automatically" closes when the mast is placed against it and remains closed until the tab is manually moved aside.
I mounted an Icom AH-4 tuner up behind the rear bumper, and bonded it to the chassis and lower mount. There are attachment points on the lower plate for additional ground radials. Initial testing shows that the tuner(sans radials) will tune the 34' vertical 80-6 meters. 20meters does tune despite the mast length being very close to a half wavelength.
To run the dipole I substitute coax for the single wire. A BNC connector fits right up through the top section of the mfj1916 mast. I wound a 1 3/8" torroid with 16 bifilar turns of #16 enameled wire as a current balun, mounted on a small disk of fiberglass with a BNC connector. The antenna is made up of two elements on each half, one for 40m (31'8") and one for 20m(16'8"). These are paralleled at the balun. Configured as an inverted V it covers each band without the need for a tuner.
I will be doing field trials this summer from the great lakes and the cape cod area.
List of pictures.
8314 Mast mounted on back of RV with vertical an dipole coax on ground.
8317 Lower mast mount
8315 Upper "capture" mount
8321 AH-4 tuner and ground strap
8324 Dipole up
8323 Close up of dipole on top of mast
8326 Dipole ready to stow
See additional photos on the gallery page click or hover over to read caption.
The MFJ-1916 similar to the Eagle-One pole.
Auto stow: Eagle 1's and other telescoping mast's have a tendency to collapse while in use due to the release of the friction only locking sections. I solved this problem by drilling a small hole near the top of each section and inserting a SS pin made from some old SS rigging wire. To avoid any alignment issues I located each hole just below the bottom of the preceding higher section. The weight of the higher sections keeps the pins in place.
No holes! Well at least no visible holes were to be drilled in the RV, as I wanted to preserve the resale value of the RV. I elected to mount the mast on the back of the RV to reduce setup time and eliminate carrying "extra stuff", though in it's present form it is not a permanent mount and the mast is dismounted when moving. The antenna is mounted on the back of the RV, and the radio is placed forward so I used the Sprinter chassis member as a wiring conduit from front to back.
The lower mount is a flat aluminum plate bolted under the fiberglass body to a backing plate with additional support provided by a threaded rod to the chassis. There is a 2" bushing on the top of the plate that accepts the bottom of the fiberglass antenna pole.
The upper mount is something I made up to "self capture" the mast, as the RV roof is too high to reach without a ladder. The dipole prevented me from using a simple hole in a plate. The mount is made of 1/4" lexan and an aluminum plate. The shape of the aluminum plate is such that it "automatically" closes when the mast is placed against it and remains closed until the tab is manually moved aside.
I mounted an Icom AH-4 tuner up behind the rear bumper, and bonded it to the chassis and lower mount. There are attachment points on the lower plate for additional ground radials. Initial testing shows that the tuner(sans radials) will tune the 34' vertical 80-6 meters. 20meters does tune despite the mast length being very close to a half wavelength.
To run the dipole I substitute coax for the single wire. A BNC connector fits right up through the top section of the mfj1916 mast. I wound a 1 3/8" torroid with 16 bifilar turns of #16 enameled wire as a current balun, mounted on a small disk of fiberglass with a BNC connector. The antenna is made up of two elements on each half, one for 40m (31'8") and one for 20m(16'8"). These are paralleled at the balun. Configured as an inverted V it covers each band without the need for a tuner.
I will be doing field trials this summer from the great lakes and the cape cod area.
List of pictures.
8314 Mast mounted on back of RV with vertical an dipole coax on ground.
8317 Lower mast mount
8315 Upper "capture" mount
8321 AH-4 tuner and ground strap
8324 Dipole up
8323 Close up of dipole on top of mast
8326 Dipole ready to stow
See additional photos on the gallery page click or hover over to read caption.
The MFJ-1916 similar to the Eagle-One pole.