Homemade base for mobile HF antenna

In the practice of a radio amateur, there is a need to work from the field or in a parking lot from a personal car.

Many radio amateurs do not have the opportunity to work on short waves from the city at all, and therefore go to the countryside, where there is less interference to reception and no unhappy neighbors. This article is devoted to a homemade base on which you can install a mast for a field HF or VHF antenna. Often in nature, it is not possible to stretch a wire antenna over a long distance from the car - there are no trees around or bushes, ditches and other obstacles interfere. Therefore, amateur car antennas for HF are Ground Plane verticals installed on the roof of a car (for example, the MFJ-1620 antenna). Their length is small - a little more than 2 meters. The antenna is matched to the cable by an extension coil with taps. But, as is known, the best long-distance antennas are not shortened ones, but full-size ones, the length of which is from 1/4 to 5/8 of the wavelength. The solution to this problem is a stand for a light, quickly erected antenna from a 7-meter high fishing rod. On such a rod, you can completely place the GP antenna web - for 14 MHz this is 5 m 20 cm with two counterweights of 5.1 m without shortening. A tripod or monopod can be used as a base or stand for a mobile HF antenna. The disadvantage of a tripod (a stand with three supports) is the price and susceptibility to wind (it is necessary to weigh it down - for example, by hanging a heavy object from the center of the tripod), the need to place it away from the car. The monopod can be rigidly fixed using an L-shaped device, which the driver runs over with a wheel. The advantages of the "under the wheel" HF antenna support are small dimensions, the possibility of self-manufacturing, high strength, and simplicity of design. This device is produced for radio amateurs in some countries and is a steel or aluminum L-shaped frame with a horizontal platform on one side and a vertical pipe on the other.

I saw the design of a homemade antenna stand on one of the amateur radio sites. The advantages of an antenna stand for running over a wheel are obvious - simplicity and strength compared to a tripod, low cost, the ability to purchase parts through online stores in your country, ease of assembly.

Components for making your own antenna stand:

• carbon rod "Mikado Princess 700" without rings (7m long), bought at the market in the fishing goods section.
• a piece of board 10cm wide, 80cm long, 2cm thick found at my dacha.
• cast iron flange with a central hole 1" for thread and 4 holes (bought it here: Flange 1" Platinum cast iron with 4 holes GEBO 329-6V)
• threaded adapter (barrel) straight from 1 inch diameter to 1 1/4 inches (bought it here: "Bochata" - transitional barrels 1 1/ 4"х1" (10/60) Valtec VTr.580.N.0706).
• Polypropylene water pipe for hot and cold water (type PN20) made of PP-R material, with an internal diameter of 30 mm. It is possible to use pipes with a thick wall, reinforced with foil, for example such.

Assembling the base

1. The cast iron flange is attached to the board with M8 screws and nuts.

2. The steel adapter is screwed into the flange using an adjustable wrench.

3. Plastic pipe - cut off a piece 80 cm long and screw it onto the base by hand.

The antenna rod with an outer diameter of 25 mm enters the base pipe and is held by its own weight without stretch marks. This ensures quick installation of the antenna. It is enough to drive onto the base board placed under the wheel and install the rod in the plastic pipe.

Reference information
Table of diameters of pipes for hot and cold water made of polypropylene
GOST R 52134-2003
Plastic water pipes are marked by the outer diameter and wall thickness, for example, 20x3.4.
Comparing pipes using the outdated PN system does not give accurate results because there are different ratios of pipe diameter to wall thickness. The most common system is SDR6, but in my case, an affordable thick-walled pipe SDR5 was used.

SDR 6 - the most common pipes with a normal wall thickness
(SDR - the ratio of diameter to wall thickness is 6)

SDR 5 - thick wall pipes
(SDR - diameter to wall thickness ratio is 5)

Example of calculating the flange diameter and choosing a polymer pipe for a HF antenna stand:

Given: the diameter of the thickest part of the rod (butt) is 30 mm

1. find the nearest larger internal diameter in the second column of the table - 33.2 mm for SDR6 with a normal wall or 30 mm for SDR5 pipes with a thick wall.
2. in the fourth column for the internal diameter of 33.2 mm, look at the diameter of the adapter thread - 1 1/2 "or 1 1/4 depending on the thickness of the pipe walls.
3. look for a flange and an adapter. Let's say we have a flange with a central hole thread of 1". Then we need a transition barrel from 1" to 1 1/2" or 1 1/4".
4. but, since we will screw the pipe in tension, it is better to take an adapter of a slightly smaller diameter - 1 1/2".
5. pipe name for internal diameter 33.2 mm, we look in the first column for external diameter 50 mm and wall thickness 8.4 mm.
   Pipe designation - will be PN20 PP-R 50x8.4, where PN20 is the pipe class (for hot water and central heating), PP-R is the material, 50 is the external diameter, 8.4 is the wall thickness (s).
   For thick-walled pipe - name PN20 PP-R 50x10 - non-reinforced polypropylene pipe, made of PP-R material.

Internal diameter formula Din=Dout - 2×s, where s is the pipe wall thickness.

Result
You will need: 1" flange, 1" to 1 1/2" barrel adapter and PN20 50x8.4 plastic pipe.

Note about the transition to a larger diameter pipe
For some rods with a diameter over 40 cm, a transition using an intermediate pipe may be required.

Example:

• 1" threaded flange
• 1" to 1" straight barrel adapter
• 40 (SDR5) or 32 (SDR6) plastic pipe, 20 cm long.
• 1" to 2" barrel adapter (Valtec VTr.580.N.0906 2" х 1")
• plastic pipe diameter 63, length 60 cm.

See full catalog of adapters - products of the firm "Valtec".

Assembly price calculation.

• board - 0 rub.
• flange - 166 rub.
• adapter 1"-2" - 480 rub.
• polypropylene pipe PN20 63x10.5 (SDR6) or PN 75x15.1 (SDR5) - 350 rub.

Total: 996 rub. ($15).
Antenna mast rod - 2000-4000 rub. ($30 - $60).

Total: 3000-5000 rub. ($45 - $75).

Polypropylene properties at low temperatures

Polypropylene is a rigid and durable material, does not crack or break when subject to load and can withstand high temperatures up to +90 degrees in continuous mode. However, the disadvantage of polypropylene is its low resistance to frost, because at -5 to -15ºС polypropylene loses its elasticity and crumbles. Even at temperatures below +5 degrees, when handling polypropylene pipes, you need to be careful: do not throw or squeeze them. The most frost-resistant grades of polypropylene are random copolymer polypropylene PP-R or Type 3 and the latest development - heat-stabilized random copolymer polypropylene - PP-RCT or Type 4. They can withstand lower temperatures.