antenna-theory.com

[Cap]

Hi,

I have an Electronics and Network Engineering background but need some advice on what kind of antenna / radio system I can use to keep in contact with my remote cabin. The cabin is 99km's from my home. There is 120vac, but no cell coverage, or copper phone lines. My main purpose is for remote telemetry with respect to cabin security as I have had a string of recent thefts out there. I am now monitoring the doors and windows with a security system and would like to communicate that status back home.

The radio link does not have to provide perfect 7x24 comms, but if it worked a few times daily that would suffice. I was thinking of using some kind of amateur packet radio link with an AX.25 data channel but again I am not sure about the antenna design. Due to the distance this is not a line-of-site application. Is it possible to "skip" an HF (shortwave 3-30Mhz) signal off the E, F1, or F2 layer of the ionosphere? What kind of antenna is best for this application? Parabolic, dipole, a horizontal or vertical wire, etc.??

Any advice would be greatly appreciated.

Thanks...............Cap

[wolberine]

99km sounds a bit far to reach with standard amateur radio equipment. have you checked around to see if there are any i-gates nearby to your cabin? these are amateur radio gateways that upload data to the internet (hence, i-gate). if they're nearby you won't need nearly as strong a transmitter or as high gain an antenna.

[Cap]

Hi Wolberine,

Thanks for your reply. After 6 days I was worried that I would not see even a single response.

Not being an amateur radio guy I had no idea i-gates existed but will do some reading/checking now. Thanks!!

Amateur radio equipment can reach thousands of km's. Check out http://www.amateur-radio-wiki.net/index.php?title=Records_-_Distance

Has anyone else ever used a data mode on amateur radio equipment? Do I need a different type of antenna design for short distances vs. very long distances? What would you recommend?

Thanks..................Cap

[wolberine]

You're right, amateur radio users can do some really crafty things to bounce messages all over the globe.

My main point was that a new user may not have the safety skills required for very high powered transmitters or how to manage a very high gain antenna.

In general, higher power levels and higher gain antennas will transmit farther distances. Just make sure to point your high gain antenna in the direction that you would like your message to be sent. If you do not want to worry about the direction of the antenna, try an omni-directional antenna and try to get it as high up as possible. This will give you a better line-of-sight to your receiver, reducing propagation (free space) losses.

As for data transmissions, amateur radio i-gates can use this data structure:

http://en.wikipedia.org/wiki/Automatic_Packet_Reporting_System

[Cap]

Thx Wolberine. I see what you meant now in your first reply. Standard ham radio gear may not reach 99km but with higher power xmtrs and higher gain antennas you can reach much longer distances.

I read the exact same link regarding APRS already. Thanks!! I will have a problem with the antenna height at the cabin. Very tall fir trees surround the area. I am reading up on ham radio antenna's on the following weblink.

http://www.ac6v.com/antprojects.htm

My preference would be something omni-directional but I don't know if a parabolic antenna would work. I have a couple Dish Network antennas I'm not using but I don't know if parabolics are designed for specific frequencies (i.e. curvature). Do you know what type of polarization would work better for me? (vertical, horizontal, or circular). Which one is the most popular for ham radio operators?

Many thanks.................Cap

[wolberine]

Unfortunately, I'm not a very experienced ham radio operator. I did some basic research and implementation for a senior project a year ago.

A vertically polarized dual-band whip worked well for our project. I think we output 1W of power.

Another route is to check your cellular coverage around your cabin. If it's decent, you could buy a high-gain cellular phone antenna. You could buy a data plan and upload your data straight to the internet. Now, you have a bit of freedom in how much data you really want to upload.

My project received APRS data and uploaded it straight to the internet with a similar set-up.

[Cap]

Me either. I dusted off my Radio Shack Pro-51 digital scanner the other day. Still works great and might come in handy with testing an APRS solution with different antenna's.

I tried a Wilson cell booster a couple years ago, but no luck. http://www.wilsonelectronics.com/Mobile-Solutions.aspx There's quite a large hill between us and the town where the cell tower is. Fortunately that's not the case with the transmission path between the cabin and home. Just some tall trees which I think I can deal with or use to my advantage. Need to factor in lightning protection as well.

I'm intrigued by your APRS project. Sounds like what I'm after. Do you mind if I ask a few questions?

- what kind of throughput you obtained (bits per second)
- how tall was the whip antenna
- how far did the whip antenna work
- what kind of ham radio did you use. I'm searching through eBay trying to figure out what's available.

Many thanks!!...............Cap

[SM2IUF]

[Cap]

Hi SM2IUF,

Thx for your detailed reply. I am very sorry to hear about your parents. I lost my Dad a few years ago and my Mom is terminally ill. These are difficult times.

I was encouraged by your email. I still have to write my amateur radio operator test but have done lot's of reading in the mean time. In fact, I communicated with the inventor of APRS who indicated that this would be a perfect applcation. Apparently some APRS radios come with up to 5 telemetry channels. However, what you did was a point-point non-data solution which I am also very interested in. I was amazed that your distance was 1100 km's and you did it with only 2 watts. I only have 100km to cover so maybe there is a chance afterall for a point-to-point link with regular HAM radio gear.

Can you help me with a few questions?

- How large/long was your dipole antenna
- Did you build it yourself, if not what was the make/model
- With an automatic keyer what would happen if someone was already using that frequency for a conversation
- what kind of radio gear did you have at each end
- what kind of bandwidth do you think this solution has
- do you think you could send a small photo since the bandwidth is very low

An update to my cabin situation is that the issue is getting worse. There has also been vandalism now. I hope to get a solution created soon and will post an update.

I look forward to your reply and any other suggestions that other forum members may have.

Cheers and thanks!!.................Cap

[SM2IUF]