Fractal TV Antenna Research & Development

[sh48]

Which fractal antenna design did you use? Most readers do not know what a fractal antenna is, so please give specifics. 20ga wire sure is thin for an antenna.

A Fractal antenna has a squiggly shape which gives good performance with a small size. It is ideal for apartment dwellers or for private antennas in a large house. And is very easy to DIY. I can post some images here, if that is appropriate. Optionally, you may view the design options at hdtv_fractal_indoor_antenna

These are the channels I receive in Richmond Hill, Ontario:-
Channel 	Network 	Location 	Remark
14-1 	Fox WUTV-DT 	Buffalo 	weak signal from directional tx
20-1 	CBC CBLT-DT 	CN Tower 	ok
32-1 	The CW WNLO-DT 	Buffalo 	ok
34-1 	My TV WNYO-DT 	Buffalo 	ok
38-1 	ABC WKBW-DT 	Buffalo 	ok
39-1 	CBS WIVB-DT 	Buffalo 	ok
40-1 	CTV CFTO-DT 	CN Tower 	no antenna needed for 790kw
43-1 	PBS WNED-DT 	Buffalo 	weak signal 156kw
44-1 	OMNI.2 	CN Tower 	ok
53-1 	CityTv CITY-DT 	CN Tower 	marginal due obstruction
64-1 	OMNI.1 CFMT-DT 	Toronto 	ok
65-1 	Global CHI-DT 	CN Tower 	ok
66-1 	Sun TV CKXT-DT 	CN Tower 	ok

[Vorg]

I am looking and redoing our outside antenna as well as making in indoor antenna. I am in Tucson Az and we have 3 directions about 120 degrees apart:
http://www.tvfool.com/?option=com_wr...aeadcb4dc1c9bb
I don't expect to get the ones at 318 degrees, with an indoor as those are in phoenix and there are mountains in the way. Also a bit of overlap in channels though ION might be nice to get. Also, only really interrested in the digital channels.

For the Indoor I was looking at doing 3 of the ruckman atennas, maybe the double version someone posted a drawing of in the replys, and facing them the 3 directions creating a 3 sided array. Then using a combiner/spliter to combine the output of the 3 baluns.

Would adding solid metal reflectors to each make the directional enough to work this way?

Can/should the 3 reflectors be tied together and to the outer shell of the 75 ohm side? I was thinking making a hole in the center of each and attaching the 75 ohm side of the baluns there as a pass through to the center where the combiner would be.

What is the proper spacing for the reflectors? From reading through everything it sounds like it should be 3.5". But I also read numbers like 8".

The original design called for #18 wire. The closest I have without going MUCH smaller is #14.


I Haven't decided yet on what I want to try for for the outside antennas. What are up there now are mostly leftover VHF from before the change cept for a yagi at ~170 degrees.

[firimari]

The versions posted here aren't actually based on the ruckman antennas, they're modified Grey-Hovermann Designs. The ruckman antenna seems to not actually be that great a design, based on a quick model I did in NEC2:

CM Ruckman Fractal 2 bay bowtie
CM AWG Gauge 14 Copper Wire Elements
CE
GW 1 3 0 0.0127 0 0 0.0127 0.0508 8.1407e-4
GW 2 3 0 0.0127 0.0508 0 0.034697 0.0635 8.1407e-4
GW 3 3 0 0.034697 0.0635 0 0.034697 0.0889 8.1407e-4
GW 4 3 0 0.034697 0.0889 0 0.0566941 0.0762 8.1407e-4
GW 5 3 0 0.0566941 0.0762 0 0.0786911 0.0889 8.1407e-4
GW 6 3 0 0.0127 0.0508 0 0.034697 0.0381 8.1407e-4
GW 7 3 0 0.034697 0.0381 0 0.034697 0.0127 8.1407e-4
GW 8 3 0 0.034697 0.0127 0 0.0566941 0.0254 8.1407e-4
GW 9 3 0 0.0566941 0.0254 0 0.0786911 0.0127 8.1407e-4
GX 9 011
GW 37 3 0 0.0127 0 0 -0.0127 0 8.1407e-4
GE 0
LD 5 0 0 0 5.8e7 0
GN -1
EK
EX 0 37 2 0 1 0
FR 0 39 0 0 470 6
RP 0 1 61 1000 90 0 3 6

This is one without a reflector, but the SWR of this antenna is way off for a 4:1 balun to a 75 Ohm coax.

As for your ideas about three antennas pointed in different directions combined using a combiner, you would be better served getting a switch. Combiners work best on two similar antennas pointed in the same direction.

[Xauto]

firimari: Thanks for the model. It looks like you need to be at 900MHz before there is plus net gain. Good for cell-phones.

[300ohm]

Yep, there is no real point to fractalizing a bowtie. All you get in essence is a shorter bowtie that resonates at higher frequencies, like a short straight whisker bowtie.
For a 2 bay bowtie, a 9 1/2 over 9 with mclapps 1 1/4 inch feedpoint gap would work much much better, and the increase in size isnt all that large.

[Vorg]

The signal will be fed to a FusionHDTV7 dual express in a Linux computer running VDR. Antenna switches are not really an option and defeat the use of a dual tuner card computer working like a tvio.

for the roof antenna, it will be feeding 4 rooms one of which will have the same computer setup, but with an extra single ATSC tuner. So I need Antennas that can pick up all 3 directions at the same time and have enough strength to driver several tuners.

If the ruckman antenna is not very good, I won't waste time trying to build it. But for the indoor antenna, it should be fairly small as space is limited in that house. Guess I'll keep looking.

"This is one without a reflector, but the SWR of this antenna is way off for a 4:1 balun to a 75 Ohm coax"

I read somewhere that is more like 120ohms. So a 2:1 would be closer to what's needed.

[Xauto]

Vorg: I do not think that you can connect antennas that are pointed in different ways with out negative effect.

[300ohm]

When two identical antennas are mounted together (ganged) and pointed in the same direction and wired together properly, there is a theoretical possibility of a 3 dB improvement. That is, twice the signal power is delivered to the TV compared to what a single antenna would do. In practice, 2.5 dB is readily achieved, 0.5 dB being the typical loss in the combining device. But if the two antennas are pointed in different directions (towards different stations) a 3.5 dB penalty for each antenna is the likely result.

The above statements are true regardless of whether the antennas have shared or separate amplifiers.

http://www.hdtvprimer.com/ANTENNAS/16bay.html

[Vorg]

Well, we don't all have all the transmitters in our area in one spot. So there isn't much choice but to have several facing in different directions. just need ways to connect them to keep negative effects as low as possible with out having to flip switches every time we change channels. That's why I asked about using a reflector to make the antennas more directional. To cut down on out of phase signals from each. We need good omni-directional antennas

[Dave Loudin]

It's not so much the antennas' mutual impedances, it's the combining of the RF from three sources. Granted, the potential signals from the other antennas may be low in most cases, but unless you can be very precise in construction and with cable lengths, you cannot guarantee that all three signals will add in phase at the combiner.

[Xauto]

Vorg: You may be able to get a Clear Stream C2 (or something like it) and remover the reflector. This will be almost omni-directional.

[sh48]

Hi: There is an interesting fractal design with photographs, circuit boards, modeling software, formulas, and so on. A bit heavy for the casual DIY but worth for a look for an appreciation of antenna design. eprints.utm.my/6680/1/79018.pdf
http://www.google.ca/search?hl=en&q=...80/1/79018.pdf

[300ohm]

eprints.utm.my/6680/1/79018.pdf

The problem with a lot of these types of analysis is that they dont compare the gain of the fractalized version with the unfactalized version. All of the antennas Ive fractalized have had less gain than the unfractalized versions. Of course, the trade-off is in size.

Bose makes great little speakers, but they doesnt really compensate for a larger size speakers IMO, correctly built and encased. Sound is transmitted by the movement of air. In other words, the laws of physics favor the larger build. IMO, same with antennas.

[sh48]

Good point. But I have 2 constraints.. limited space and multipath interference. I get more reliable reception from weaker signals. That is, for co-located transmitters, the digital is good when the analogue is snowy and digital is erratic when the analogue is strong but has ghosting. Even with a small antenna, I can see Buffalo from my window. A bigger antenna might not be helpful. Investigation continues.. Cheers

[stampeder]

sh48, your 2 constraints seem pretty severe, especially given that others in Richmond Hill have excellent reception of many Canadian and Buffalo, NY stations. What are the details of your situation that you feel you have to resort to a fractal antenna?