How to make small HF antenna?

[armadi]

I am looking to do some experiments with short range (< 100m) HF signals using small antennas, but I know very little about antennas and how to make them efficient.

I want to transmit a 5 MHz carrier and pick it up at ranges from 10m - 30m. I want to use small antennas to do this. When I say small I mean something portable, preferably < 1m on the largest dimension. Furthermore I'd like to be able to test both monopole/dipole and a loop antenna.

Considering that a 5 MHz signal has a wavelength of ~60 m any antenna with those dimension are bound to be pretty poor in itself and will need some matching.

My idea for making an okish monopole is to simply simulate a monopole of a given length, say 60 cm, find the impedance and then make a matching circuit that can match from a 50 Ω coax to a whatever Z the antenna is.

For making the loop I figured using the formula for an LC circuit:
Frequency = \[\frac{1}{2*\pi*\sqrt{L*C}}\]

Wind a loop, calculate the inductance and use the above formula to find the approximate C and then tune the C until the resonance hits the right frequency.

For both I'll use ferrite beads clipped around the coax as chokes/baluns.

I'm using lab equipment for this part, so a signal generator generates the signal and I check for a signal on a 200 MHz oscilloscope.

Is this approach feasible? Do I need something other than the matching circuit for the monopole and does the loop require a matching circuit? Is the ferrite beads enough, or do I need something more to stop signals running down the coax shield?

Any help and pointers are welcome.

 

[vfone]

Loop antenna is the best solution for such low frequencies and small antenna dimensions.
The radiated resistance of a small loop antenna is low leading to low antenna efficiency, but anyway there is no other better option for small antenna compared to this wavelength.
Matching network of the loop antenna doesn't help too much increasing radiated power, but it helps to minimize the TX reflected power. On the receive side the same, might help to match the LNA for minimum noise figure (gamma optimum).

 

[ferdows]

for HF antenna we need matching circuit in the Small Antenna Design by Douglas B. Miron you can find method for design them

 

[armadi]

for HF antenna we need matching circuit in the Small Antenna Design by Douglas B. Miron you can find method for design them

Thanks for the reference. I'll have a look.

 

[Externet]

The way I have done a somewhat acceptable short range compact antena is by feeding a 50 ohm transmitter to a 50 ohm coaxial and the antenna itself being a non-inductive 50 ohm resistor with some 'whiskers' or coils as extended as permitted by space constrictions at each end of the resistor.