UPDATE on Seeking Ideas for RoadTesting Antennas

Having spent time in a previous life doing RF work for the NZ Post Office (later Telecom) I've seen a vaste array of antennas, and antenna designs.

Each has a specific purpose, and some are designed for the environment, so they have special charateristics or materials.

As awneil said the radiation pattern and gain are the key differences between antenna.

The examples above are all omni-directional, (but for different bands) so the gain is the final figure as to how well it will perform.

Therefore the 2.7-6GHz version should have a longer range with the same power.

To test these you need a transmitter with adjustable gain, and a receiver that can provide the RSSI (Received signal strength).

They need to be tested in an open environment, clear from reflections.

While this provides the optimal conditions, in reality they are used in an urban environment, placed to suit the box or mounting.

This means the real world result is varied and not able to be duplicated easily.

What I think might be useful is to see if the testers can increase the range of the middle example by directing it, to provide a cheap link between two points.

I've aluded to some antenna theory here BT_Sentry : Zero Emission Detection

I have to build something that will allow my modifications to be tested, which is likely to involve a servo and stand in the middle of a paddock.

Cheers

Mark

Hi Mark,

While the gain is indeed a measure of how well the antenna performs, to calculate the range you need to take into account also the frequency of the signal (assuming all the other parameters are identical).

The Omni-directional SMD Antenna and the OMNI ANTENNA, 2.7-6GHZ, 5DBI, ADHESIVE both work on similar frequency bands, so looking at their datasheets, we can already infer the OMNI antenna performs better (higher gain).

To establish which has a better range between the OMNI ANTENNA, 2.7-6GHZ, 5DBI, ADHESIVE and the OMNI ANTENNA, LINEAR, 433MHZ, 0.7DBI, we can use the Friis Equation - (aka Friis Transmission Formula). The distance R can be calculated as:

R=√(Pt·Gt·Gr)·c√Pr·4πƒ

where:

   c is the speed of light

   f is the frequency of the signal transmitted

   Pt is the power transmitted

   Pr is the power received

   Gt is the gain of the transmitting antenna

   Gr is the gain of the receiveing antenna

To simplify,  lets assume the power transmitted, the power received and the receiving antenna's gain are the same for both antennas. Lets call R1 the range for the 5dBi antenna, and R2 the range for the 0.7dBi. If we calculate the ratio R1/R2, we get:

R1R2 =√Gt1Gt2 ·ƒ 2ƒ 1

where:

    Gt1 = 5dBi = 3.16 ,    f1=2.7GHz  (lets use the lower end of the band)

    Gt2 = 0.7dBi = 1.17 , f2=0.433GHz

Calculating, we get:

R1R2 ≈0.26   

Therefore, under the assumptions above, the 0.7dBi antenna should give a range about 4 times longer than the 5dBi one.

Fabio

to calculate the range you need to take into account also the frequency of the signal

of course ... and yes you're quite right that the losses increase with frequency.

I mistaken assummed that the testing would be on antennas in the same band

Mark

To establish which has a better range

It may be interesting to some ... we had much better signal to noise ratios not by increasing the power, but reducing the bandwidth of the receivers.

Many of our receivers were capable of being used across the band they were designed for, but in reality they stayed on a fixed frequency, for varying reasons.

Careful tuning reduced that to a narrow frequency, and thereby reducing the noise floor.

Many of these receivers have no filtering on the front end, and therefore wide bandwidth antennas can provide higher background noise.

Trying to extract the signal you're after in amongst the noise, can be a struggle, but is dependant on the hardware and techniques used.

Mark

To establish which has a better range

It may be interesting to some ... we had much better signal to noise ratios not by increasing the power, but reducing the bandwidth of the receivers.

Many of our receivers were capable of being used across the band they were designed for, but in reality they stayed on a fixed frequency, for varying reasons.

Careful tuning reduced that to a narrow frequency, and thereby reducing the noise floor.

Many of these receivers have no filtering on the front end, and therefore wide bandwidth antennas can provide higher background noise.

Trying to extract the signal you're after in amongst the noise, can be a struggle, but is dependant on the hardware and techniques used.

Mark