Loop antenna glued on back of cow-Gain question
Loop antenna glued on back of cow-Gain question
(OP)
Gentlemen,
I am developing a tracking system operating at 433 MHz that utilizes a loop antenna glued in the horizontal plane to the back side of a cow.
The diameter is 1/4 wave and it will be spaced 1/4 inch from the skin. The height above ground will be 4.5 feet.
According to www.chipcon.com application note AN003, the impedance of flesh is 38-57 ohms (page 15). Pages 5-8 give a lot of information on loop theory but dont help me solve the following problem.
I need to predict propagation. What would be the relative gain of this loop in the horizontal plane compared to a standard 1/4 wave whip and ground plane?
I cannot use a whip in this application.
Thanks very much for your help.
Jim
I am developing a tracking system operating at 433 MHz that utilizes a loop antenna glued in the horizontal plane to the back side of a cow.
The diameter is 1/4 wave and it will be spaced 1/4 inch from the skin. The height above ground will be 4.5 feet.
According to www.chipcon.com application note AN003, the impedance of flesh is 38-57 ohms (page 15). Pages 5-8 give a lot of information on loop theory but dont help me solve the following problem.
I need to predict propagation. What would be the relative gain of this loop in the horizontal plane compared to a standard 1/4 wave whip and ground plane?
I cannot use a whip in this application.
Thanks very much for your help.
Jim





RE: Loop antenna glued on back of cow-Gain question
I've actually seen a finite-element model of a cow (seriously), but I can't find the link. It was in relation to studies of the absorption of RF as relates to safety of RF. Probably overkill for this application to conduct a complete NEC4 analysis. Given the application - tracking large, slow moving animals that are presumably located in a known area, it shouldn't be difficult to achieve a more than adequate RF margin (low duty cycle).
By the way, have you considered a simpler to install, and more comfortable to the cow, collar?
Are you using GPS ?
RE: Loop antenna glued on back of cow-Gain question
Collars snag in ranch environments and do not place the transmitter in the physical position we need it. GPS is not used for cost and coin battery life issues.
ANOTHER QUESTION. How will the beam pattern change? Will the horizontal donut flare upward or downward? Will nulling of the electric near field by the cow be sufficient to make the pattern horizontally symetric?
RE: Loop antenna glued on back of cow-Gain question
I don't have sufficient related experience to answer your question.
You might want to investigate the cell phone safety issue because those researchers have done a lot of work with antennas near heads. You might find some related info.
Another alternative is to use an up-to-date NEC to model your antenna near ground (where the ground parameters are adjusted to match your hip-of-beef).
Also, you could just try several antennas. Perhaps the link margin is such that you don't even need to worry about optimised RF performance.
What kind of range ('Home, home on the range...' - sorry) are you planning? What sort of peak power and duty cycle?
RE: Loop antenna glued on back of cow-Gain question
Emperical testing is always the best way to be sure. I plan on it. Just getting a head start.
Jim
RE: Loop antenna glued on back of cow-Gain question
RE: Loop antenna glued on back of cow-Gain question
Kevin.
PS: Patches are easy to make, and change if water sits directly on it, so you'll need to cover it with 1/4 to 1/2 inch thick material. I made a very similar antenna for an aircraft last year, same frequency coincidentally.
RE: Loop antenna glued on back of cow-Gain question
RE: Loop antenna glued on back of cow-Gain question
The propagation models i have checked say things should work. Antenna is the question...
What would the configuration of the Patch be?
Thanks Jim
RE: Loop antenna glued on back of cow-Gain question
Let me know if you have equipment to tune the patch if you place it in a cavity.
The configuration would be cow, aluminum foil 12" square or so, foam spacer, patch, foam spacer, plastic waterproofing cover(ziplock bag). The transmitter can sit in the foam spacer just to the side of the patch. Antenna weight should be less than one pound.
Patches are narrow band and bandwidth is proportional to their thickness, so it'll need to be tunable to get to the right frequency.
Kevin
RE: Loop antenna glued on back of cow-Gain question
RE: Loop antenna glued on back of cow-Gain question
kch.
RE: Loop antenna glued on back of cow-Gain question
The cow will have an intrinsic impedance of about 50 ohms though I dont know what that means as far as minimizing coverage. I would love to get a diagram of any suggestions.
The cow skin does need to breath.
W1VT of the ARRL has graciously turned be on to EZNET so now I can analyze simple antenna structures over the simulated elevated back of a cow.
One question I have with this program is that I have data that the intrinsic impedance of a cow is probably 50 ohms. However EZNET requires logal ground characteristics to be entered in S/m and dieletric constant
I do have access to a friend with a network analyser. And prototyping is easy if I volunteer to be the Cow!
Thanks,
Jim
RE: Loop antenna glued on back of cow-Gain question
Another point is that the receiver antenna can have quite high gain if it is installed to one side of the 'range'. Also, a vertical array can add futher gain by compressing the pattern along the horizontal. If the receiving antenna is installed in a very high location, then the cosecant-squared pattern would be useful. All in all, there is an opportunity for substantial antenna gain, perhaps as much as about +13dBi, at the receiving end by optimally designing the receiving antenna and carefully selecting its location. Worth including...
PS: Hopefully, we won't be finding any bits of electronics in our hamburger...
RE: Loop antenna glued on back of cow-Gain question
RE: Loop antenna glued on back of cow-Gain question
How do you know that a watermellon is a viable substitute?
BTW I was on my hands and knees saying moo yesterday.
Jim
RE: Loop antenna glued on back of cow-Gain question
Kevin.