Telemetry Frequency for 30-40 Miles Monitoring

I used to play around with antennas some. I once used an antenna matcher and turned my patio umbrella into antenna.

Line of sight, or reflected? I'd think ARRL might have some references for the antennas.

Take a look at the two links here.

ionospheric propagation
This program is self-contained and ready to use. It does not require installation. Click this link GrndWave3

You want to run QRP on some of the most QRM laden bands (HF) with a single long wire? I wish you luck!

Even with a complex antenna such as a quad loop beam you will have trouble picking up such a weak signal in a field of noise.

You would have a much, much better chance at 50 mHz or above, but you still require specialized antennas, they are just more complex. The downside is the directionality of the signal.

However, the higher the frequency the less power will be required. Any way to get a line of sight transmission between transmitter and receiver.

I agree that above 50 mHz would be best. Give us some more information about the terrain between locations and also what time(s) of day will the transmissions take place.

You may need a directional antenna in any case, but they are not that hard to build if cost is any issue.

The telemetry device is a Beeper of survived after a severe earthquake. Set up antena, and turn on the switch, the device continuously transmits until the battery(LiiON 6V) dies. Because celular phones, land-lines as well, become unusuable for couple of hours, the beeper is the only means for signaling safety from husband to wife. This case, there's no mountain range or anything to interrupt the transmission between transmitter and receiver. Yesterday, I tried 7MHz and it was very HARD to receive such QRP signal of extremely low S/N. If a direction antena is easilly set up, VHF 50MHz is promissing. Long wire and reflector of matching wavelength, I will try again, just change the Xtal and replace tank coil, a piece of cake. Let you know.

this case. .

The best way may well be to use near vertical maim lobe radiation pattern horisontally polarised aerials, both Tx & Rx, and ionispheric reflection.

Minimised low angle lobes will cut QRM & QRN on the receiver. A good ground-plane will make this possible.

This worked for a friend who provided coms for oil platforms about 1970.

Passing enough current (DC or AC) through the stainless wire will oxidise it if visability is a problem.

The band choice boils down to, smaller aerial, reduced part of the day.

Even under the best of conditions ionospheric reflection is not a reliable mechanism and propagation effects change drastically with frequency, sun spot activity, and time of day.

Also, the short distance between transmit and receive points will make the angles of incidence and reflection from the ionosphere virtually impossible. The radio transmission will simply pass through the ionosphere.

In order for radio waves to "skip" the angle of incidence must be very low on the horizon and low in frequency. Skip propagation is designed for transmission beyond the horizon and the distances cited by the original poster are much too short.

Finally, 0.1 Watt of transmission power is simply too little power to do the job.

What you are proposing will not work, even with high gain antennas.

Who will operate the transmitter? Check to see if you can legally do this as most situations require the station to have the licensed operator present.

That's a very good idea.

Well a quick check of your frequencies indicates you plan on using the amateur bands. I don't think you can use 18MHz as it appears to be part of the Maritime and Aeronautical band.

I really don't know much about the Japanese radio spectrum and broadcasting standards and regulations but have worked with something similar (abit much shorter range).

As an emergency beeper wouldn't you need it to be able to operate through rubble (such as a fallen building) or are you just thinking more along the lines of locating people stranded on their building roofs with clear line of site back to the receiving antenna(s).

Based on my experience (and if it were me looking at this project) I would also look into trying to utilise the existing cell phones so many people have (and will have with them in the event of an emergency), basically a simple temporary emergency cellphone tower network with a software app for the cell phones to send a low power low bandwidth location 'ping' or text message. I think this has been considered using a low cost aerial deployment system (a blimp with a cell phone repeater).

Here is another example product I was thinking of (for potentially-competing product market perspective)

http://www.pcworld.com/article/226182/atandts_portable_cell_tower_is_useful_in_natural_diasters.html

Yes they did spell disasters wrong (oops).

Wow! $15K without the genset for only a 1/2 mile coverage? But it's a great idea.

Good signal strength up-to 2Kms

the power output to 200-250 milliwatts,

on with matching 50-ohm ground-plane antenna or multi-element Yagi antenna,

Coil winding details are given below:
L1 - 4 turns of 20 SWG wire close wound over 8mm diameter plastic former.
L2 - 2 turns of 24 SWG wire near top end of L1.
L3 - 7 turns of 24 SWG wire close wound with 3mm diameter air core.
L4 - 7 turns of 24 SWG wire-wound on a ferrite bead (as choke)

Adjust potentiometer VR1 to set the centre frequency near 100 MHz.

Nice circuit, but the author needed something good to as much as 64 kilometers or 32 times the range that circuit provides.

Is it possible with a small circuit like the above one?

It depends.

You have so many factors involved. You have frequency. You have local QRM (RF noise generated by the environment (other radios, stations, electrical equipment, electrical grid, etc.). You have QRM generated by the sun and the Earth's electromagnetic field in the ionosphere, which varies by time of day and the solar sunspot cycle.

You also have to consider the terrain and any obstacles that may block the signal. Then you have atmospherics. Even rain, snow, or thunderstorms impact reception.

I once made a two way contact into southern Africa from Pennsylvania using 1 Watt of transmit power and a 240 foot loop of wire 30 feet in the air on 10 meters. However, the conditions were just right.

That being said, it is easier to get longer distances under those conditions than short distances of 60 kilometers under any conditions with such low power. The HF (shortwave) band is inherently a very noisy part of the RF spectrum. By its nature it is best suited for very long communications and the reason it is still used as a means to beam radio services such as the Voice of America, BBC, Radio Moscow, etc, around the globe.

240 foot loop of wire 30 feet in the air on 10 meters.

I think you are good with conversions also .I still wonder why mile and nautical miles are 800 feet longer than a statute mile?

All i want to say is one should a good meteorologist before doing some stuff with RF .

QRZ

The antenna is dubbed a sky loop or horizontal loop. It has a unique property of loading up very easily on its harmonic frequencies as well as it's fundamental frequency.

I cut mine for 80 meters (probably should be about 265 feet) and it will perform on 40, 20, and 10 with increasing gain (within limits). The other nice properties of the loop is it inherently rejects noise and is omnidirectional while being horizontally polarized.