That's actually really cool.
But it was far too technical for me to decipher exactly how/why it works.
I have basic high school physics knowledge, which ends at simple coils/magnetism, electric circuits and motors :P

If that could be done (effectively) for UHF, anyone and everyone in an older neighbourhood could enjoy free tv, without needing to put up anything! (well, aside from a coil around their tree.)

That was my response too (except that I did phys 12 by correspondence and got behind so that I crammed the last 1/3 of the course into the first week of the summer after graduation -- retention of knowledge was minimal). Definitely cool. If I didn't have the internet to play on I'd probably try it so that I could play with shortwave.

actually used the tree as the antennaI should have been clearer.

The problems UHF frequencies have with vegetation and obstacles apply exactly to the idea of using a tree as a helical or toroidal antenna (which is what your given web site actually is talking about). Helical and toroidal antennas are not suitable for broadband reception - they are for specific single frequencies. You could theoretically build a helical or toroidal TV antenna using plastics or wood but you'd have to pick which channel you want to get, or you'd have to devise an automatic tuner so that when you change channels on your television the antenna would reconfigure for that channel in real time. Also, as I mentioned, motion of the antenna is the enemy of Digitial OTA.

With the amazing SBGH and DBGH antenna designs already available to the public for DIY projects (see their own threads) it would not make sense to try something else.

So, using a tree as a TV antenna (mount) is not advised.

Is that clearer? ;)

FWIW, the 600 meter band is around 500KHZ Read: Below AM RADIO!!!

That's just a little bit different than UHF TV :)

Thanks Stampeder, totally clear now. Though, I have lots of trees ... I suppose I could have one tree per channel if not for the other issues.:)

Anyhow, I've got a home-made db8 right now doing nicely and have been dragging some old pvc piping I have lying around into a pile with the intent of trying out the DBGH.

I just made one a week ago and its red hot. Folded dipoles have 2 advantages being inherently broadband and have a feed impedance close to 300 ohms. When stacked 1/2 wave apart all in phase the final impedance presents a better match than with phased conventional or bowtie dipoles.

Mine is made from 3/4 inch PVC conduit for the mast and the elements are made from 1/8 inch alum welding rod formed into 9 3/8 inch by 1 inch wide elements sized for the center of the UHF band.

It has no reflectors so is bi-directional to get the USA and Ottawa stations from Embrun without a rotor. Its also getting a bunch of VHF and UHF analog stuff too. A reflector on each element would give it even more gain but then it would become uni-directional.

Anyway its simple to make, cheap, a very good performer, and has growth potential if you want more elements.

I just made one a week ago and its red hot. Folded dipoles have 2 advantages being inherently broadband and have a feed impedance close to 300 ohms. When stacked 1/2 wave apart all in phase the final impedance presents a better match than with phased conventional or bowtie dipoles.


How did you feed them to get them all in phase?

Did you use a single phase line or single feed lines for each element back to a common point or some other combination?

Sounds interesting

I've been testing a Homemade 4 bay bowtie it uses 12" long whisker elements and they are spaced 11 3/4" vertically. It has a curved screen reflector and forward swept elements.

I've had it up for over a month now.

Computer modeling shows it to have a gain of about 15.5 dbi on channels 25 and below.

It was built in an effort to receive a distant station on channel 18 and to my surprise it also works very well well up into the 40's and also is a able to receive VHF-HI stations 40mi away 2 edge with no drop outs.

http://www.frontiernet.net/~mclapp/Antennas/4%20bay12in/4bay%20lo%20freq%20front%20view.jpg

The 8 folded dipole elements are stacked vertically 1/2 wave apart for 600 mhz or about 9 3/8 inches. This puts them 180 degrees out of phase if parallel feed is used so the feed lines are criss crossed over between elements to get them in phase. Feed is picked off the top 4 at the bottom of number 4 element using a 1/2 wave long piece of 300 ohm twin lead and the bottom 4 likewise from the top of number 5 element where the two lines are connected in parallel and therefore in phase to a short 6 ft length of 300 ohm down to the pre-amp located below the array.

The thing works very well with high gain as it beam forms in the vertical yet is bi-directional. It has sharp nulls off the ends so its not a true omni but getting close. I did some experimenting on the back deck using an S meter in a converter box I have and found if I tip it off the vertical more than about 10degrees the signal was lost so it is basically looking right at the horizon. Its mounted on the roof about 35 ft high and doing a great job.

Feed is picked off the top 4 at the bottom of number 4 element using a 1/2 wave long piece of 300 ohm twin lead and the bottom 4 likewise from the top of number 5 element where the two lines are connected in parallel and therefore in phase to a short 6 ft length of 300 ohm down to the pre-amp located below the array.Are the inter-element feed lines open wire or 300 ohm twinlead?The thing works very well with high gain as it beam forms in the vertical yet is bi-directional. It has sharp nulls off the ends so its not a true omni but getting close.With 8 stacked dipoles the vertical beam width would be very tight, no doubt that the signal drops off quickly when tilted much away from vertical. Sounds like by the way you described the pattern that it is working just as it should. It's really tough to get all those elements in phase but it sounds like you pulled it off. Good work

I like your 4 bay bowtie with curved reflector, nice job.

The inter element feeds are open wire made from insulated #12 speaker wire I had laying around. They cross over as in your antenna only mine has 4 over 4 with a 1/2 wave 300 ohm feed from each group of 4 to a common 300 ohm feeder down to the pre-amp. I guess its only really "in phase" at 600 mhz but seems to work well over the whole UHF band and gets VHF too.

I first tried a crude 8 bay bowtie with no reflector made on a board and it also worked very well but the folded dipole model is a little better and built to handle the weather. Its on the roof so hard to get a picture without some climbing which I really hate doing.

I finally succeeded! using my homemade Yagi in the attic from my house in Laval.

My Yagi is made of a wooden boom and the elements are made of 1/4'' threaded bars from homedepot. The driven element is a folded dipole, the ends are built using two U-bolts connected to the bars with unions. There are 9 directors for a total of 11 elements.

I could not catch it before because the antenna was not high enough. Raising the antenna by two ft made a whole world of difference. By mounting the antenna as high as possible, the space in the attic is limited so I had to limit the boom length to about 2.2m

I followed the calculations by VK5DJ, the element lengths, the reflector, the driven element and the first 5 directors follow the dimensions given by the program to about plus/minus 2 mm. Because the boom length is limited, I compressed the remaining available length to accommodate the other 4 directors so their spacing is about 20 cm. I read that the spacing can be between 0.1 and 0.2 wavelegth (14 and 28 cm for VHF 13).

My Yagi and my DBGH are joined to a CM7777 preamp and feeding three TV. I might try later with the GE amp from Addison using a UHF+VHF combiner. The GE used to work better for me than the CM7777 with my UHF antenna. I am using the CM7777 now because it has a separate VHF and UHF inputs.

One thing I find strange is splitting the signal to 3 TVs did not significantly affect the signal meter on my tv for VHF 13. I thougth that every time you split, you lose 3dB per split but in this case, it didnt reduce the strength at all. It seems to stay around 49 to 50. I will attempt to fine tune later by playing with the antenna location. Maybe adding more parasitic elements will help with the gain.

The cost of building this antenna is approximately:
- wooden boom: $4
- four 1/4'' x 72'' threaded bars from homedepot 4x$2.75
- two u-bolts: $5
- balun: $1
- misc. screws and nuts: $2
- fun building and experimenting: priceless!

so the cost is under $30 with taxes

Please find below some pics.

This is my DBHG in the attic
http://groups.msn.com/Hungwatches/misc.msnw?action=ShowPhoto&PhotoID=270

This is the Yagi with the folded dipole. The ends are built using U-bolts
http://groups.msn.com/Hungwatches/misc.msnw?action=ShowPhoto&PhotoID=279

Another view
http://groups.msn.com/Hungwatches/misc.msnw?action=ShowPhoto&PhotoID=273

TVfool data
http://groups.msn.com/Hungwatches/misc.msnw?action=ShowPhoto&PhotoID=288


Signal Meter on my Toshiba TV
http://groups.msn.com/Hungwatches/misc.msnw?action=ShowPhoto&PhotoID=286

hungt1999, Your Yagi is very nice! I'll like to make one also! But I don't get it the balun is only connected to the "folded dipole" with the U-bolt? I am also scared that I have to build my antenna IN my attic... because I don't think it will fit by the attic door! It's only 38" wide... =/ lol

Where did you take your measurement to build the Yagi ?

Danv: there are several Yagi calculation programs out there, just do a google search on "Yagi design" or "Yagi Calculator" and you will find several on-line programs that will help you.

You just need to enter the frequency you want (in this case, it is 213 MHz for ABC on VHF 13), the rod diameter you intend to use and the program will give you the optimum dimensions.

Here is a 4 bay antenna I made with the frame made of PVC. It uses about 2 lengths of PVC (6) 90's and (6) Tee's, the one pictured uses (4) 90's and (2) 45's. The whisker elements are 10" long and are spaced 9 3/4" apart, the phase lines are #14 gauge wire and the elements are #10 gauge wire.

The reflector was made by stringing #20 galvanized wire back and forth through the PVC side frame and tensioning with a turn buckle.

http://www.frontiernet.net/~mclapp/Antennas/PVC%204%20bay/PVC%204bay%20front-side%20with%20dimensions.jpg

Computer modeling shows a 13.5 - 15 dbi gain across the UHF channels 14 - 50 with a peak near 15.5 dbi.
and about 0 - 4 dbi with a peak near 6 dbi on VHF-hi.

It has about 20 db front to back ratio and a beam width of 35 - 40 degrees.

I've been doing some testing with a spectrum analyzer and various antennas which shows this antenna to be very close to those specs. I hope to be able to share some of these tests soon, I've still got to get all the data in the computer.

I can supply more details on building this and similar antennas if any one is interested.

This puts them 180 degrees out of phase if parallel feed is used so the feed lines are criss crossed over between elements to get them in phase. Feed is picked off the top 4 at the bottom of number 4 element using a 1/2 wave long piece of 300 ohm twin lead and the bottom 4 likewise from the top of number 5 element where the two lines are connected in parallel and therefore in phase to a short 6 ft length of 300 ohm down to the pre-amp located below the array.


So you have a total of 6 criss crosses, 3 per each 4 pair set ?

So you have a total of 6 criss crosses, 3 per each 4 pair set ?
Yes exactly, 3 between the top 4 and 3 between the bottom 4. Elements 4 and 5 are connected to a common point with 1/2 wave long 300 ohm feeders NOT crossed over so there is 1 wavelength of feeder between these elements. The feed to the pre-amp is off that common point.

I experimented on the back deck with an S meter using a number of other feed configurations and this one worked best.

Another question, are the folded dipoles broadside to the transmitting station or laying in a flat plane towards it ? The reason I ask is, are the criss crosses crossing over the other folded dipoles or not.

http://farm4.static.flickr.com/3006/2826229488_abe3ce1c2a_o.jpg
http://farm4.static.flickr.com/3282/2826229430_76714cfb83_o.jpg

The dipoles are flat side facing the horizon. The feed lines are on the back side of the mast opposite to the elements.

I see, I went to the direct flicker link. Not sure why your photos dont show here.


It looks like the dipoles are screwed into the side of the mast. What size ID is that pvc pipe ?