EMRFD Message Archive 13399

Message Date From Subject
13399 2016-12-24 11:16:21 Chris Howard w0ep Antenna pattern with a drone
Would it be feasible to have position indicators on
a small flying drone, and a signal strength meter,
and fly the drone around and map the signal coming off
of an antenna?

w0ep
13400 2016-12-24 11:28:12 Vern VanZ Re: Antenna pattern with a drone
don't know why not. Could be a bit of work tho depending on your level of skill. With a small transmitter and micro (i.e., MSP430, Arduino, etc) to read signal level from the FS meter, readings could be relayed back.  Or...Depending on the micro used, you could simply record GPS coords and FS levels, then upload and plot once the drone has returned...

Sounds like a fun project to me.
Good luck!
73,
N7GTB - Vern


13401 2016-12-24 11:56:35 Chris Trask Re: Antenna pattern with a drone
It would be far simpler to have the transmitter on the drone and record the received signal strength with a more sophisticated receiver than the drone could handle.

It would be nice if the drone could somehow be programmed to use a GPS receiver and keep itself stationary.

>
>
>Would it be feasible to have position indicators on
>a small flying drone, and a signal strength meter,
>and fly the drone around and map the signal coming off
>of an antenna?
>


Chris

When the going gets weird, the weird turn pro
- Hunter S. Thompson
13402 2016-12-24 11:58:32 Phil Sittner Re: Antenna pattern with a drone

Chris-

Tom Schiller, N6BT, did a presentation on this very topic at this year's Pacificon. You can try emailing him through his website, n6bt.com.

Phil kd6rm


13403 2016-12-24 12:07:49 w3lpl2000 Re: Antenna pattern with a drone
A small low power transmitter is more practical, make the received
power measurement on the antenna under test.

The real trick is the antenna!

73
Frank
W3LPL

13404 2016-12-24 13:06:27 Tayloe, Dan (Noki... Re: Antenna pattern with a drone
I had thought about using a marker generator to do this.  If it was then keyed with a distinctive pattern, you could readily identify it against the band noise.

- Dan, N7VE

Sent from my Windows Phone
13405 2016-12-24 15:43:41 Tayloe, Dan (Noki... Re: Antenna pattern with a drone
A small whip antenna, perhaps 12" pointed straight down would probably produce a pretty spherical pattern.

- Dan, N7VE

Sent from my Windows Phone
13406 2016-12-24 18:01:28 kb1gmx Re: Antenna pattern with a drone
The pattern will be that of a monopole or may be truncated dipole. Inefficient at that.

Now the bigger issue is near field measurement of far field?

For a pattern that matters to other people it must be far field which begins 
at least one wavelength away from the antenna if very small and 5x as a starting
point for a full size dipole.  For 80M that's 400M! and the signal will be mighty weak.

I's also place a better than even bet the resulting pattern if measurable will not 
match expectations.  Measuring HF antenna patterns is very difficult. I've done it 
at a commercial site and had to debug the site.

The idea of a drone is interesting but position error and accuracy will likely be higher than
acceptable for accurate results.

Allison
13407 2016-12-25 07:30:41 Bob Re: Antenna pattern with a drone
This is an interesting and creative question.  GPS is currently used for many drones.  Some can be programmed to automatically cover a flight pattern.  

A standalone GPS has some limitations on accuracy.  Differential GPS, with a ground based GPS, would improve your accuracy tremendously.  

You may need to lower your power to a minimal level to not overload the onboard receiver.  

Bob
WA2I
13408 2016-12-25 07:37:29 Bob Re: Antenna pattern with a drone
"Now the bigger issue is near field measurement of far field?"

Interesting point Allison.  Would measuring both the ground level and elevated pattern give a better estimate of far field?  My (perhaps naive) impression is a far field pattern comes from the altitude signal and the near field signal is mostly from the azimuth.

GPS is poor at measuring altitude because of geometric constraints.  Many drones have barometric sensors to measured relative altitude.  These sensors have impressive accuracy for altitude (I think the accuracy is within a few centimeters).
Bob
WA2I
13409 2016-12-25 08:55:13 Mark Schoonover Re: Antenna pattern with a drone
I would think you'd need to fly many wavelengths away to get reasonable measurements even when running low power. It's an interesting experiment that's for sure. 

13410 2016-12-25 08:55:44 eugene_mah Re: Antenna pattern with a drone
Sure, see [1505.05885] Beam calibration of radio telescopes with drones

 

13411 2016-12-25 08:56:33 eugene_mah Re: Antenna pattern with a drone
Sure, see

[1505.05885] Beam calibration of radio telescopes with drones

 


Eugene/AB4UG
13412 2016-12-25 12:12:05 kb1gmx Re: Antenna pattern with a drone
>>>Interesting point Allison.  Would measuring both the ground level and elevated pattern give a better estimate of far field?  My (perhaps naive) impression is a far field pattern comes from the altitude signal and the near field signal is mostly from the azimuth.<<<

Yes, no, and sorta.   

The far field is the fully developed fields close in you may see the "inductive fields" which are not 
always the same.  In professional circles there are a set of rules to know which is applicable and 
what the difference is.

For ham use FAR field is applicable.  It does not involve inospheric reflections only the actual 
antenna pattern and its interaction with things like other incidental radiators and scattering 
stuctures such as random wires (like house wiring), guys,power lines, shallow buried conductors. 
Those interactions define the pattern at distances typically more than 5 to 10 wavelengths.

A good example is a mid height dipole say 35ft up and a mobile 10 miles away that can bare hear 
a 400W signal while the op with a dipole is working VKs.  The pattern at low angles may be very 
weak at a distance but close in say 100Ft it will appear to be strong maybe until you nearly 
overhead the antenna by 100FT.  

Usually to measure the full hemisphere is very difficult and the  are very few places you can 
do that (commercially) at HF.  As areas with nulls will be quite weak and others angles may 
be very strong.  Typical experience I've had at UHF is 60DB and HF has been greater with 
small antennas.

If you run the path loss equation for signal with varying distance you can see if a few feet error
will corrupt the accuracy of the result.


Allison

 
13413 2016-12-25 13:36:21 w3lpl2000 Re: Antenna pattern with a drone
Antenna pattern measurements have been performed with transmitters
and antennas mpunted on balloons and airplanes for at least fifty years.
Perhaps the best known and most widely used implementation was
Stanford Research Institute's XELEDOP system. 

The easiest modern method is to use a low power signal source such
an an Elecraft XG3 with a short dipole antenna made of light weight
whip elements.

The maintaining accurate known position and antenna orientation
and reliably lifting the required payload weight are the primary
problems to be solved.   Don't be surprised if a few quadcopter
crashes occur during the learning phase of your project!

W8WWV recently performed actual antenna measurements using a
similar quadcopter based signal source.

73
Frank
W3LPL


13414 2016-12-26 16:02:00 Brooke Clarke Re: Antenna pattern with a drone
Hi:

I think there are 3 conditions for far field: Tx-Rx Distance: >>physical size of the antenna, >>wavelength and >
Fraunhofer distance.
https://en.wikipedia.org/wiki/Near_and_far_field
https://en.wikipedia.org/wiki/Fraunhofer_distance
http://www.prc68.com/I/Ant.shtml#Pattern - comments on the papers referenced in this thread
In the case of an HF antenna at 160 meters this is a little short of a mile. Can a drone fly a mile high?

The real question may be how does the antenna perform for given Tx and Rx station locations. For an antenna operating
at VHF and higher frequencies the answer is close the what the pattern says (the exception is Fresnel zone effects), but
for an HF antenna the big factor not covered by the pattern is the ionosphere.

One way to take that into account is to use a Chirp Receiver as a way to characterize a receive antenna (I found this to
be an excellent method):
http://www.prc68.com/I/RCS-5A.shtml
Which gives a plot where the X-axis is frequency (2 to 30 MHz) and the Y-axis is time delay. So you "see" the various
layers of the ionosphere as they effect the signal between Tx and Rx.
It also points out the different quality metrics for Tx vs. Rx antennas. While the pattern is symmetric for Rx and Tx
the quality metric is very different.
For a Tx antenna getting the most power to the Rx antenna is the key parameter (not VSWR, not pattern).
For an Rx antenna getting the highest Signal to Noise ratio from the Tx direction is the key parameter (not VSWR, not
pattern).

Another way may be by using WSPR, but I haven't tried that yet.
https://en.wikipedia.org/wiki/WSPR_(amateur_radio_software)
<https://en.wikipedia.org/wiki/WSPR_%28amateur_radio_software%29>
http://physics.princeton.edu/pulsar/K1JT/devel.html
http://dev.wsprnet.org/drupal/

Another way is to use ALE (but only after figuring out the best antenna to support its special needs).
https://en.wikipedia.org/wiki/Automatic_link_establishment
http://hflink.com/

--
Have Fun,

Brooke Clarke, N6GCE
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
The lesser of evils is still evil.

-------- Original Message --------
> Antenna pattern with a drone
13415 2016-12-27 06:27:05 kb1gmx Re: Antenna pattern with a drone
Wow, Stanford Research Institute's XELEDOP system!  That is in my non-ham 
career window of experience.  Its one of those things few here have knowledge of.
Its also not without its problems.

Don't forget helicopters too.

Testing antennas for gain and pattern is part art and heavy science.  At least 
if one is to get consistent results.  Its tough to model then get correlation
least on a regular basis. 

Drones with the right location tools may be useful presuming they can carry 
a load.  However for swept measurements there are as they say, issues.

Allison
13416 2016-12-27 07:36:53 kb1gmx Re: Antenna pattern with a drone
A drone at more than 400-1000ft altitude is both hard to see and a hazard to navigation for 
aircraft transitioning the area.  As a pilot I have some experience with that.

Therein lies the issue as at lower HF especially getting far enough away to be in the far field
rather than Fresnel zone or inductive field.  At the same time having enough signal to be above 
the measurement noise floor can be challenging.

One item often forgotten is for most antennas the ground(earth) under you is part of the 
system.  The reflection and absorption of the earth is factor in any HF antennas performance.

The biggest issue is that at a given frequency height is related to wavelength.  For example
a 10M antenna at 65ft (20M) is  wavelengths up and expected to be good performance 
but, a 160M dipole that high is barely a 1/8th (.125) wave up and is just about on the dirt 
so to speak.  So height is measured in altitude compared to wavelength.

To that I say three rules apply:

* If you want more signal use more metal (elements, wire, etc).
* If you want more signal get the antenna (the metal your using) higher.
* If all else fails remember any antenna is still better than a bucket of 
  wire(or metal) in the shed.


Allison