eHam

eHam Forums => FoxHunting => Topic started by: GCANHAM on December 02, 2019, 06:48:58 AM

Title: Yagi Antenna for rocket TX
Post by: GCANHAM on December 02, 2019, 06:48:58 AM
  I'm a avid rocket hobbyist.  One of the biggest heartaches a rocket flyer can experience is loosing a rocket due to high winds or unpredictable flights. I have my technician license (KC1KMI) and two ht's (BF-F8HP and Anytone 878).  I've recently purchased a 70cm RF Transmitter Beacon.   https://shop.bigredbee.com/products/70cm-16mw-transmitter

I plan on installing this in the avionics bay in my rocket so as to have some type of beacon to hopefully locate the rocket should it drift into the woods.  My question is:

1) What would be a inexpensive Yagi antenna or any antenna that would suffice in finding a lost rocket.
2) Would building my own Yagi be possible and how would I tune it.

Thx for you advice in advance.

Geoffrey
Title: Re: Yagi Antenna for rocket TX
Post by: W9IQ on December 02, 2019, 07:16:52 AM
Here is a nice construction article for an antenna designed for exactly the same purpose.

http://www.rustynailworkshop.com/archives/12 (http://www.rustynailworkshop.com/archives/12)

(http://www.rustynailworkshop.com/wp-content/uploads/2010/10/shapeimage_1.png)

- Glenn W9IQ
Title: Re: Yagi Antenna for rocket TX
Post by: W1VT on December 02, 2019, 08:09:30 AM
https://www.wa5vjb.com/yagi-pdf/cheapyagi.pdf
AFAIK the clever feed design first appeared in the ARRL Publication Understanding Amateur Radio.
Kent developed a collection of cheap but effective antennas for his friend in Cuba.

Zak W1VT
Title: Re: Yagi Antenna for rocket TX
Post by: WB6BYU on December 02, 2019, 06:59:51 PM
In fact, if you look closely at the photo of the antenna that Glen posted, you can see
that it uses the WA5VJB feed method, and the element spacing is typical of his designs
as well.  So I'm guessing that is where the original design came from.

I've build a whole lot of antennas for transmitter hunting, including some yagis (and quads)
for  70cm, but the yagis are based on the WA5VJB designs (with some tweeking to center
the passband where I want it, etc.)  So I'd just be repeating what has been said before.

The last antenna used PEX pipe (which is light), and I've also used thin-wall PVC.  I rotate
the driven element 90 degrees about its axis so the fed end of the driven element is in front
of the main part rather than underneath it, allowing it to also pass through holes drilled in
the pipe.  I then cut a notch in the top, solder the coax directly to the driven element, and
fill the notch with hot melt glue.  The coax runs out the back end of the pipe, with a tie wrap
for strain relief.

I typically use #12 solid copper wire for the driven element and #8 aluminum ("ground wire"
from Radio Shack) for the parasitic elements to save weight, but on 70 cm that isn't much of
a problem, as the antenna is relatively short and light.

Somewhere around 4 - 7 elements is probably a good size.

You will find that, once you get close to the transmitter, it will saturate the receiver and you
won't be able to take a good bearing without some sort of attenuator.  Hopefully at that point
you can triangulate and get a good estimate of where it actually is.


Oh, and remember to confirm that the transmitter is on before launching.  One of the
local universities lost a balloon due to that minor issue...
Title: Re: Yagi Antenna for rocket TX
Post by: GCANHAM on December 03, 2019, 07:47:49 AM
   Wow, thank you everyone for such great advice and direction.  The red bee tx is my first attempt at setting up some type of recovery beacon should a rocket drift beyond the fly field.  Truth be told the idea of a tx and a receiver RDF approach is somewhat old school to finding lost rockets.  There are so many ways of locating a lost rocket these days.  This will probably be my next project:  http://eggtimerrocketry.com/home/eggfinder-gps-tracking-system/  (Eggtimer TRS GPS Tracker/Flight Computer).  But what I like about both these systems (red bee tx or the Eggtimer TRS)  is that they require a FCC license.  So it just goes to show that the ham radio hobby permeates many other hobbies as well.  Again thx for all the great advice and help.

Geoff KC1KMI