Well done, Congratulations!
You have connected shield of coax (through white wire) to cut-edge of the can, which has reversed the polarity of groundplane.
Try to connect the shield/white wire to flat bottom of the can, close to its center. This will most likely improve maximum range & number of planes.
Spider VS COCO
Same rooftop Location, same amp, same Pi2, same settings, swapped simple spider for 8x112.4mm segment COCO. (optimized for Velocity Factor)
This COCO performs slightly better than my production COCO which has 8x111mm segments.
Cheers!
LitterBug
Thanks, I’ll give that a go.
It’s obviously nowhere near as good as my outdoor 8 leg spider with amplifier (though that seems to have decreased in performance lately) but for something so simple it’s definitely a good place for a beginner to start without having to buy any adapters or coax.
Msg rates right now are 880 vs 240
Great piece of work! Good experiment. Well done LitterBug.
My best CoCo is 8-element, open top, 114 mm element length, made of RG6 of unknown VF.
One & half years ago, I purchased a 75 ft (23m) coil of RG6 coax from a Dollar Store for Canadian $7.99. This was unbranded and no specs available.
Since RG6 have VF between 0.8 & 0.85, I set to start making CoCos using different lengths between 110 mm & 117 mm. Over a period of last 1½ years, I repeated following process innumerable number of times, till I hit the gold mine at 114 mm:
make > test > throw in garbage 
.
The copper cores are useful for making spiders!
abcd567,
I started @ 115 and kept shortening by 1mm till the numbers went down instead of up (around 111). The VF adjusted optimal length was pretty close to my best results and went with that majik 112.4. In my case, it was easy to push the solid center conductor in, snip the foam/braid/foil/casing, then push the center conductor back out. Would have been much harder to do if I had to use a swirly finger cutter thingy… 
I’m finding that there is a small 1-2% difference in power inserters too. Going to have to pop open some of the cheap ones and mod/upgrade the internals to try to match the results from my DirecTV inserter.
Cheers!
LitterBug
Two antennas recently got married. The wedding was rubbish but the reception was fantastic 
Great! Thanks for sharing your experience! The magic 124mm element most probably requires impedance matching, a situation like Franklin Spider. I will try 8-element 124 mm coco with & without impedance match when I get time and have appetite to do it.
Nicely and smartly worded! 
Corrected that to 112.4mm
Oops.
Ohhh, I thought you are refering to the element length worked out by the special formula:
Element Length =½ wavelength x [2 x VF / (1+VF)]
The special formula gives a near perfect phasing and hence much higher gain than the standard formula:
Element Length = ½ wavelength x VF
The special formula Coco has much higher gain than standard formula Coco, but has disadvantage of very high antenna impedance which requires impedance matching network.
Without impedance matching, the special formula Coco gives poorer performance than the standard formula Coco.
Now some reverse engineering:
Your optimum element length = 112.4 mm = your VF x 275/2 mm
your VF = 112.4 mm/ (275/2) mm = 0.8175
My optimum element length = 114 mm = my VF x 275/2 mm
my VF = 114 mm/ (275/2) mm = 0.83
Is there any merit to building a spider or cantenna based on 5/8 wave instead of 1/4 wave measurements ?
5/8 wavelength spider results in
Lower Gain
Higher SWR
Poor Radiation Pattern
Please see below 3 simulations
1 of 3: whip 1/4 wavelength, radials 1/4 wavelength
2 of 3: whip 5/8 wavelength, radials 1/4 wavelength
3 of 3: whip 5/8 wavelength, radials 5/8 wavelength
Simulation 1 of 3: Whip 1/4 wavelength, Radials 1/4 wavelength
Simulation 2 of 3: Whip 5/8 wavelength, Radials 1/4 wavelength
Simulation 3 of 3: Whip 5/8 wavelength, Radials 5/8 wavelength
The simulations posted above were done using software 4NEC2.
I have now done the simulations again, this time using software MMANA-GAL.
The Gain in the two simulations are quiet different. 4NEC2 shows reduction in gain, while MMANA-GAL shows increase in Gain.
The SWR in two simulations tally, and both show a very high SWR.
MMANA-GAL Simulation 1 of 3: Whip 1/4 wavelength, Radials 1/4 wavelength
MMANA-GAL Simulation 2 of 3: Whip 5/8 wavelength, Radials 1/4 wavelength
MMANA-GAL Simulation 3 of 3: Whip 5/8 wavelength, Radials 5/8 wavelength
Very interesting - thanks for the analysis.
I am wondering if it’s worthwhile adjusting the length of the telescopic antenna that came with the Nooelec USB SDR to be either 1/4 wave or 5/8 wave (or as close to it as feasible) instead of just leaving it fully extended.
Can’t hurt to try… You may learn something!
LitterBug
I put it at 5/8 wave (or as close to it as you can’t really see the feedpoint in the telescopic antenna but I assume it’s close to level with where the coax exits the antenna).
Has any modeled the FlightAware antenna that is currently on Amazon ?
Sorry, I dont have details of Flightaware antenna (design, dimensions), so I cannot model it.
**Suggestions: **
(1) Place the magnetic base of telescopic antenna over the lid or bottom of a large food can made of iron. This will help in 2 ways:
(a) The magnet in antenna base will cling to the can and hold antenna in position.
(b) Antenna’s 1 inch dia base magnet provides the groundplane (the braid of coax is connected to it). This is too small a groundplane. When magnet clings to the food can, the food can will enlarge the groundplane and reception will greatly increase.
(2) After purchasing DVB-T dongle, the very first thing you should purchase is a pigtail, with MCX male pin at one end (for dvb-t) and F-female connector at other end to connect regular antenna coax (RG6, RG58 etc).
The MCX male connector of pigtail is delicate, and sometimes breaks.Better order 2 pigtails, one in use, one spare, to be immediately available if mcx connector of one gets damaged. These are not costly ($3.80 + free shipping from China)
http://thumbs3.ebaystatic.com/d/l225/m/mdrImDH82MNX8tYr1OYk0sA.jpg http://m.ebay.com/itm/F-female-nut-bulkhead-to-MCX-male-RG316-cable-jumper-pigtail-15cm-/320847773379
http://thumbs4.ebaystatic.com/d/l225/m/mnn821kGZ8JMM1I-6zITnuw.jpg http://m.ebay.com/itm/RG174-6inch-RF-pigtail-F-TV-female-jack-pin-bulkhead-to-MCX-male-straight-Cable-/251399601339
**(3) Please also see this post:
.
This is post #701 for this thread started by JPolch in November. I’d like to take a second to express my appreciation of the broad range of topics and information that have been posted. I have learned much and avoided many ****-ups. Thanks to all the posters.
joel posting from sites 704 - 10333 :mrgreen:
The difference from moving an antenna from inside to outside is huge. At least double the message rate.
My double glazed windows definitely prevent a lot of EM signals getting in.
Simple cantenna initially with about 1m coax inside to 6m coax (2 x 3m premade with F connectors linked) outside. Only set it up because I now have a spare RPi and RTL-SDR dongle to play with.
Plus an old bit of meccano
Though it’ll probably go rusty too quickly.
Not the best picture because it was getting dark.
