C -Band Omni range

[nautica]

Any insight for the possible practical distance achievable by a C-Band (4-6 GHz) Omnidirectional antenna is greatly appreciated.
I know there are many parameters affecting the distance but once you have 10-20 Watts transmitter power and an 360 deg.(Azim.) & 70 deg. (ELEV.) how far you can transmit before going below lets say 0 dBm at this band?
Any relating equations for the distance and omni characteristics?

 

[VEBill]

You can search on the 'Free Space Loss' equation (include the constant '32.45' in your search terms).

 

[nautica]

Thanks VE1BLL.. I came across several constants in free space loss. But it is based on isotropic antenna.
1)Is 32.45 additive or subtractive?
2)I wonder is there any loss equation related to azimuth and elevation angle specs. of omni?
Thank you again..

 

[VEBill]

The 32.45 constant falls out when the formula for pathloss is reduced to the simple equation that uses MHz and distance (I assume that you've found the formula by now).

With respect to your omnidirectional antenna (and covering 70 degrees in elevation), it sounds like a simple low gain antenna, perhaps a simple vertical. The gain might be something around +1 or +2 dBi.

Obviously you'll have to include the antenna gain at the other end.

If you needed to extend the range, then the easiest thing to change would be to use a high gain omnidirectional antenna - one that covers a narrower elevation range. This assumes that your clients at the far end are confined to the Earth's surface.

 

[SolderingGunslinger]

It has been a while, however I think I my calculations are correct. An omni-directional antenna with a 70º vertical half power beamwidth is around 7 dBi gain.
10-20 watts = 10-13 dBW.

Assuming no transmission line losses, EIRP=17 to 20 dBW.

Dbm=dBW + 30, so again assuming no transmission line losses, EIRP = 47 to 50 dBm

At 5GHz, a 50dB transmission loss is less than five feet.

As VE1BLL said, you will need to factor the gain of the receive antenna and any transmission line losses into the equation.

I remain,
The Old Soldering Gunslinger

 

[SolderingGunslinger]

...And another Thing...

Remember, at 4 to 6 GHz, we are talking about ionizing radiation. Even with a 7 dBi gain antenna, I don't think I would like to spend too much time close to the antenna as it would be around 100 W EIRP...I can almost feel the vitreous humor in my eyeballs start to get warm now.

--SGS

 

[VEBill]

"...ionizing radiation..."

No it isn't (ionizing).

 

[Higgler]

Omni antenna gain is approx. 112/elevation beamwidth in degrees, so your omni antenna gain is maybe 2 dB peak, but set it at zero dBi gain just for some ripple that might occur in azimuth. Use a Pentel Pencil head, 0.5 mm size and stick it in an sma female connector, works good from 4-30 ghz.

10 watts is +40 dBm, so losing about 40 dB going from this transmitter to your receiver with identical zero dBi antennas leaves only 40 dB space loss with zero dBi omni antennas.

6 ghz space loss at 40 feet is 70 dB.
cutting the 40 feet in half 5 times reduces the loss another 30 dB (6 dB loss reduction for distance change by a factor of 2) hence 40 feet changes to - 20,10,5,2.5, 1.25 feet distance to lose 40 dB and arrive at your zero dBm number. 15 inches distance with 10 watts transmitted gets you zero dBm at your receive antenna.

not very far.

Most receivers on Network Analyzers are good to -70 or -90 dBm. You need sensitivity to go far. A 40 dB drop is not much.

kch

 

[SolderingGunslinger]

6gHz space loss at 5-Ft is 50 dB

Using the old gain/Isotropic calculation using the surface area of a sphere / the area of the surface illuminated by the theoretical antenna, I come up with an approximate 4.1dBi gain for your antenna, however, I was wrong when I posted above, so take it with ta grain of salt...some days the grey matter works, others...well...

Assuming Higgler's 2 dBi antenna gain and 20-watts input to the antenna, the FCC power density guidelines of less than 1 mW/cm^2 (above 1.5 GHz) for an uncontrolled environment would be exceeded at about 1/2-M from the radiation center of the antenna. The controlled environment FCC Guideline of 5 mW/cm^2 for the same frequency would be exceeded any closer than about 23 cm from the center of radiation.

The formula is: S= PG/4?R^2

Where S= the power density in (appropriate units)
P= power input to antenna (in appropriate units)
G=power gain of antenna over an isotropic source (expressed numerically, not in decibels)
R=distance from center of radiation (in appropriate units)

I realize that the distances involved are sufficiently close to the antenna to require little additional protection than placing the antenna on a short tower, however if the application requires the transmiting antenna to be in an indoor workplace environment, some protection might be needed.

I remain,

The Old Soldering Gunslinger

 

[SolderingGunslinger]

The question mark in teh formula should be Pi...so much for inserting greek letters...harumph!

--SGS

 

[VEBill]

To ensure clarity:

http://www.google.com/search?q=define:ionizing+radiation