[bokakob]

Hello everyone!

This weekend I built the Centipede-4 antenna prototype. I built it out of wood plank frame and regular household electrical wires. This antenna performs very well. Prior to this antenna I was able to count 22 total channels, with this antenna the count went up to 37. Below is the picture and the model file. If you built Centipede series antenna (2-4-8) and would like to share the results, please post your info in this thread. Thanks, BOKAKOB.

CM "Centipede_Large" High Gain UHF Antenna
CM Copyright 2010 © BOKAKOB All Rights Reserved
CE
GW	2	11	0	0.05	-0.375	0	0.295	-0.375	1.63182e-3
GW	3	13	0	0.05	-0.375	0	0.295	-0.25	1.63182e-3
GW	4	13	0	0.05	-0.375	0	0.295	-0.5	1.63182e-3
GW	5	11	0	0.05	-0.125	0	0.295	-0.125	1.63182e-3
GW	6	13	0	0.05	-0.125	0	0.295	0	1.63182e-3
GW	7	13	0	0.05	-0.125	0	0.295	-0.25	1.63182e-3
GW	8	11	0	0.05	0.125	0	0.295	0.125	1.63182e-3
GW	9	13	0	0.05	0.125	0	0.295	0.25	1.63182e-3
GW	10	13	0	0.05	0.125	0	0.295	0	1.63182e-3
GW	11	11	0	0.05	0.375	0	0.295	0.375	1.63182e-3
GW	12	13	0	0.05	0.375	0	0.295	0.5	1.63182e-3
GW	13	13	0	0.05	0.375	0	0.295	0.25	1.63182e-3
GW	14	11	0	0.06320211	0.61776985	0	0.295	0.5	1.63182e-3
GW	15	3	0	0.025	-0.125	0	0.05	-0.125	1.63182e-3
GW	16	7	0	0.025	-0.125	0	0.025	-0.25	1.63182e-3
GW	17	7	0	0.025	-0.25	0	0.025	-0.375	1.63182e-3
GW	18	3	0	0.025	-0.375	0	0.05	-0.375	1.63182e-3
GW	19	1	0.013	0.01	-0.245	0	0.025	-0.25	1.63182e-3
GW	20	3	0	0.025	0.375	0	0.05	0.375	1.63182e-3
GW	21	7	0	0.025	0.375	0	0.025	0.25	1.63182e-3
GW	22	7	0	0.025	0.25	0	0.025	0.125	1.63182e-3
GW	23	3	0	0.025	0.125	0	0.05	0.125	1.63182e-3
GW	24	1	0.013	0.01	0.245	0	0.025	0.25	1.63182e-3
GW	25	11	0.013	0.01	-0.245	0.013	0.025	0	1.63182e-3
GW	26	11	0.013	0.025	0	0.013	0.01	0.245	1.63182e-3
GW	27	11	0	0.06320238	-0.6177704	0	0.295	-0.5	1.63182e-3
GW	28	11	0	-0.05	-0.375	0	-0.295	-0.375	1.63182e-3
GW	29	13	0	-0.05	-0.375	0	-0.295	-0.25	1.63182e-3
GW	30	13	0	-0.05	-0.375	0	-0.295	-0.5	1.63182e-3
GW	31	11	0	-0.05	-0.125	0	-0.295	-0.125	1.63182e-3
GW	32	13	0	-0.05	-0.125	0	-0.295	0	1.63182e-3
GW	33	13	0	-0.05	-0.125	0	-0.295	-0.25	1.63182e-3
GW	34	11	0	-0.05	0.125	0	-0.295	0.125	1.63182e-3
GW	35	13	0	-0.05	0.125	0	-0.295	0.25	1.63182e-3
GW	36	13	0	-0.05	0.125	0	-0.295	0	1.63182e-3
GW	37	11	0	-0.05	0.375	0	-0.295	0.375	1.63182e-3
GW	38	13	0	-0.05	0.375	0	-0.295	0.5	1.63182e-3
GW	39	13	0	-0.05	0.375	0	-0.295	0.25	1.63182e-3
GW	40	11	0	-0.0632021	0.61776986	0	-0.295	0.5	1.63182e-3
GW	41	3	0	-0.025	-0.125	0	-0.05	-0.125	1.63182e-3
GW	42	7	0	-0.025	-0.125	0	-0.025	-0.25	1.63182e-3
GW	43	7	0	-0.025	-0.25	0	-0.025	-0.375	1.63182e-3
GW	44	3	0	-0.025	-0.375	0	-0.05	-0.375	1.63182e-3
GW	45	1	0.013	-0.01	-0.245	0	-0.025	-0.25	1.63182e-3
GW	46	3	0	-0.025	0.375	0	-0.05	0.375	1.63182e-3
GW	47	7	0	-0.025	0.375	0	-0.025	0.25	1.63182e-3
GW	48	7	0	-0.025	0.25	0	-0.025	0.125	1.63182e-3
GW	49	3	0	-0.025	0.125	0	-0.05	0.125	1.63182e-3
GW	50	1	0.013	-0.01	0.245	0	-0.025	0.25	1.63182e-3
GW	51	11	0.013	-0.01	-0.245	0.013	-0.025	0	1.63182e-3
GW	52	11	0.013	-0.025	0	0.013	-0.01	0.245	1.63182e-3
GW	53	11	0	-0.0632024	-0.6177704	0	-0.295	-0.5	1.63182e-3
GW	1	3	0.013	-0.025	0	0.013	0.025	0	2.65e-3
GE	0
EK
EX	0	1	2	0	1	0
GN	-1
FR	0	1	0	0	470	0

 

[hkaye]

I built a centipede-2 prototype awhile ago. Here are the details of some of the construction techniques I used.

I soldered the balun, and the copper wires together. I used JB weld epoxy to glue the antenna to the wood.

For the bottom, I used a wooden shish-ca-bob stick and epoxied the antenna in place.

Using epoxy I was able to set it up. Adjust for accurate dimensions and tape it while the epoxy dried over night.

-------

The antenna has great results. I find it very directional. Unfortunately from my location (because I'm in an apartment and the building blocks a good bunch of channels) I can receive all the digital channels from Toronto, Hamilton and two in Buffalo. I can get the same channels from a biquad and pre-amp - so I'm not using this antenna to it's full potential.

 

[stampeder]

For our members who don't follow the Area 51 thread but wish to build an antenna, why would they want to build the Centipede instead of an M4 or a GH?

 

[hkaye]

I guess everyone situation would be different. These are my observations. I built a GH prototype (left) and a centipede-2 prototype (right) -

The GH antenna worked well. However, the design is a bit big, since I would try to mount this antenna in a window in my apartment. From where I am, the GE Futura antenna performed identically to the above GH prototype. So I just used the GE Futura antenna.

The centipede-2 is smaller in size which works well for putting it in a window. It also performed better than the above GH, picking up to extra digital channels - the two omni channels from Toronto.

So, for me the smaller size was the selling factor when it came to the GH vs the centipede-2.

My current setup is a double bi-quad that I run through a pre-amp. It's the smallest size antenna, gets all the channels that the centipede-2 gets. It's not as directional so I don't have to adjust the antenna when picking up Buffalo vs Toronto.

As they say, your mileage may vary. I'm in a 15th floor apartment about 56 miles away from Toronto and 83 miles away from Buffalo (WNLO + WNED).

 

[stampeder]

I'm in a 15th floor apartment about 56 miles away from Toronto and 83 miles away from Buffalo

So at the deep to deepest fringe (KW from Downtown Toronto and from Buffalo) you have the advantage of being high up, thus the luck with the Futura too.

Has anyone had the chance to test a Centipede at ground level or at about 25 feet (typical rooftop antenna height?

 

[bokakob]

why would they want to build the Centipede instead of an M4 or a GH?

Since that was a philosophical question here is a little of philosophical answer prior to some other answers:

"Dogma is the established belief or doctrine held by a religion, ideology or any kind of organization: it is authoritative and not to be disputed, doubted or diverged from." http://en.wikipedia.org/wiki/Dogma

A few practical answers based on the theoretical performance evaluated with the help of an excellent program 4NEC2:

- this antenna is twice as sensitive at low channels compared to GH meaning that it would pull in stations either from more far away or those hidden behind obstacles.

- this antenna has much wider beam patter compared to M4 meaning that this antenna either does not need to be aimed precisely or it could pull in more scattered stations.

- this antenna occupies less cross-sectional area compared to physical size of GH meaning that it is more efficient thus more polished.

- this antenna doesn’t need elaborate tuning and custom made reflectors, it will work right after it is finished, meaning that if this antenna would receive equal amount of research time spent on GH and M4 it would probably be even better yet.

- this antenna looks cool and I like it.

Ref. Link comparing SBGH and C2 (C4 has higher specs):
http://www5.picturepush.com/photo/a/2813153/img/Antennas/Composite.png

Regards, BOKAKOB

 

[stampeder]

When it comes to antenna designs we certainly don't rest on laurels or dogma around here! I'm partly the devil's advocate here, partly the devil.

For the DIY antenna builder looking for the best antenna would you say then that the C2, C4, C8 should be their first choice over a GH or M4?

 

[bokakob]

For the DIY antenna builder looking for the best antenna would you say then that the C2, C4, C8 should be their first choice over a GH or M4?

Theoretically Centipede-2 (C2) is much comparable to SBGH antenna with +3dbi better gain on low channels, smaller size and easier mounting details (comparison here: http://www5.picturepush.com/photo/a/2813153/1024/Antennas/Composite.png and here: http://www2.picturepush.com/photo/a/2852055/1024/Antennas/Centipede-2-W1x2in-Reflector.png).

Centipede-4 (C4) is better than SBGH and it compares favorably with M4 having much wider horizontal beam pattern -- still easier to build and mount

Centipede-8 (C8) is very well comparable to DBGH and has better gain at low channels and smaller size. It should outperform SBGH and M4. Again, it should be easier to build and to mount to a single pole.

In my mind C4 is very easy to build, I made it under 3 hours. It has better and wider gain than SBGH, it can be made out of any wire on hand.

There is something in the fact that all antennas (C1, C2, C4 and C8) are based on the same wire pattern. It is not coincidental.

Based on these arguments I would start with a basic Centiped unit (C1 here: http://www1.picturepush.com/photo/a/2849009/1024/Antennas/Centipede-1-Composite.png ) to learn and to get familiar with this shape; and then progress to Centipede-4 (here: http://www4.picturepush.com/photo/a/2896707/1024/Antennas/Proto.png) instead of SBGH antenna.

Until proven otherwise I hold my grounds.
Regards, BOKAKOB

 

[balm]

Centipede-4 (C4) is better than SBGH and it compares favorably with M4 having much wider horizontal beam pattern -- still easier to build and mount

not sure your basis for this statement, but the M4s, at least in the models I looked at are at least as wide beamed, if not more than the C4, can you tell me which models your using for this comparison?

the biggest disadvantage I see with Cs is the lack of performance for VHF, or VHF-Hi, again at least on the models,....I would build this in a minute if I could figure a way of getting some decent gain on VHF-hi, like the M4, without losing on the UHF, so far I havent been able to model it, with many configurations and NARODS...

Bokakob, congratulations , keep up the good work

 

[hkaye]

Come spring/summer I'll build a centipede-4. I have a real challenging reception situation at my mom's place. Here's my reception results/challenges I posted last year -

http://www.digitalhome.ca/forum/showpost.php?p=1009783&postcount=819

http://www.digitalhome.ca/forum/showpost.php?p=1011515&postcount=823

I tried both the magic GE futura antenna and the GH. I added some foil as a reflector with still no luck. The massive green monster is hindering reception despite the tvfool.com graph showing very favourable conditions for getting tv channels.

 

[bokakob]

I already tried to answer this question here: http://www.digitalhome.ca/forum/showpost.php?p=1059144&postcount=6

 

[ota_canuck]

I had a C2 on my tower at 35ft up until a week ago. It was very sensitive to large trucks passing by. Pixelation and dropouts occured every time a large vehicle passed by. I tried the C2 with and without a preamp and the same problem persisted so I gave up on it for now. I don't have that sensitivity problem with the 4221 or GH antennas. It could be the element design or it could be the phasing line layout. I have a feeling that the complexity of the phasing arrangement may be the culprit. I haven't had much time to experiment with this C2 recently, however I'm going to try various phasing line gaps, arrangements etc to see if the oversensitivity problem can be resolved.

The C2 definately has a wider beamwidth than a GH or 4221 and it pulls in all the signals that are available better than the GH or the 4221, however it is not useable in it's present state of over sensitivity to reflections.

I have worked with another design very similar to this C2 design with good success with both VHF & UHF reception without having any pixelation problems. I'm not so convinced that the current C2 design is user friendly enough for the novice builder. Though if these sensitivity bugs can be worked out, the C2 may very well become a superior antenna compared to a 4221 or a SingleGH design.

I can't comment on the M4 antenna because I have not tried building one yet.

If I can I make one recommendation for the purpose of posting performance comparisons, I would suggest that comparisons should remain within the same level of antenna design.. example a C2 should be only compared to a 4221, a single GH, a M4. There is no point comparing a C8 design's performance to a 4221, a single GH or a M4 design.

And let's always keep it in mind that an antenna of any design that works in one particular application may be totally unsuitable in another location due to outside inteferences and terrain conditions etc.

 

[ota_canuck]

Bokakob,

- this antenna looks cool and I like it.

I agree !

 

[stampeder]

Agreed - this is where real world discussion takes over.

BTW I asked Bokakob what a suitable short form name for the Centipede would be and he agreed on the C2, C4, C8, etc.

Just don't tell any law enforcement agencies that you are up on the roof ready to try out your C4!

 

[nwusa]

I am trying to determine what would work best for me to as far as a DBGH or Centipede to test instead of my xg91 stack. Has anyone used a reflector with a centipede to help with the front to back ratio, or am I not doing enough of my own homework? Would this not help with the sensitivity to other objects too?

 

[ota_canuck]

nwsa,

That's what I mean't about partiticular applications. I my case the market is wide spread and it would take several different antenna aims with a rotor or several ganged antennas to cover all of the markets. My best choice would be an omni-directional or bi-directional approach to avoid the need for using a rotor for aiming every time I want to change channels.

If you don't mind a rotor, then a more directional antenna would likely give you more overall mileage. If your in an area where there are too many adjacent channel or co-channel problems, then a good directional antenna with a good reflector would be the best choice.

 

[mclapp]

reflector notes

I like the looks of the centipede it appears to be fairly compact and somewhat easy to build.

I only have the centipede large NEC file posted in this thread so I ran it to see how it looks.

It has nice gain, I'm not sure if it's a c4 or c8 but it has about 2 db more RAW gain than a 4 bay with 9 1/2" whiskers and 9" bay spacing non reflected.

The 4 bay had a wider 3db beam width by about 6-7 degrees

I didn't run all the frequencies or VHF-hi just took a snap shot of a few to see the differences.

One word of caution the centipede will have the same pitfall as the n bay antennas have, the high voltage points are at the natural mounting points of the antennas elements. In a n bay style antenna this will detune the antenna somewhat from what the computer models say. That will effect both actual gain and resonant frequency. Since some of the centipede builds I've seen have the elements attached to the mounting frame on both ends that's detuning times 2.

I did a quick wire mesh reflector measuring 50" tall x 30" wide, spaced 4" back and it responds good boosting gain by about 4db RAW but the SWR went up on some frequencies. The forward beam width got narrower by about 9 degrees. Keep in mind that's not optimised in any way just a quicky reflector model. Net gain shows to be about 16.5dbi around ch35 that may not be the peak, just one of the few channels I modeled.

 

[nwusa]

ota_canuck

I totally understand and agree with you about each application being different.

I started out with one xg91 and found my signals fading in and out, and so I added another xg91 to hopefully stabilize the signal and it did help some but with the weather lately the signals are wondering again. I chose the xg91 for its directivity and gain factor as the channels I am looking for are almost all from the same direction ranging from about 60 to 75 miles. What I am having problems with are those that are in the 38 and 39 range and the xg91 strength is lower at those channels as opposed to the the higher channel 48. These three channels are all in the same two or three block location, and 48 is rock solid and 38 and 39 are intermittent. I know my location could deffinately be a factor, but I also know I am dealing with the gain limitation of the xg91s even stacked.
I feel your pain since it sounds like you need a rotor. I am fortunate in that I shouldn't need one, but having issues with distance, and signal strength. It also turns out 38 and 39 do not have the signal strength that 48 does, so I have that working against me too.

So, seeing a good comparison between a DBGH and a C8 Centipede with a reflector, or maybe even narods would be interesting I would think. Just thinking out loud.
Good luck to you.

 

[300ohm]

BTW I asked Bokakob what a suitable short form name for the Centipede would be and he agreed on the C2, C4, C8, etc.

Unfortunately that may cause confusion with the Antennas Direct new model names. (I cant see the logic of the A-D naming scheme, except for maybe "C" = circle ? "L" for loop would have been more logical IMO, heh. )

 

[stampeder]

That's a good point about confusion with the AD model numbers, and heaven help us with publishing plans, documents, etc., if there were ever to be trademark issues!

I suggested BC2, BC4, BC8 etc. (as in Bokakob's Centipede) so maybe we need to keep that idea on the table. Bokakob?