It is the length of the wire that makes it resonate to a specific frequency. For example, my FOX station (channel 27) is at the 550 frequency whose wavelength is 21.5 inches. I made a whisker for my bowtie antenna at 10.75" x 2 to maximize my FOX reception. That is the specific wire length at which the maximal energy transfer occurs for that frequency. Smaller or larger lengths mean less than optimal energy transfer at that frequency. Most antennas are a compromise (average) in size between the lowest and highest frequencies in a band. It is not the size but the resonant frequencies that characterize an antennaâs efficiency. In some respects an antenna is a set of tuning forks that resonate to certain âvibrations.â
Using FOX here is what I observed. With the antenna whiskers at 10.75", the SNR for that station was 25 (85%). With the antenna whiskers at 9", the SNR was 21 (70%). With the antenna whiskers at 12", the SNR was 23 (75%). Just like Goldilocks and the three bears (porridge bowls).
Okay. So, no world splitting star-trek warp coil thing.
But, being more serious. when you attach the whiskers to the bowtie (that is such a weird statement), why does it not count as making the bowtie longer?
Or, I guess another way Iâm trying to wrap my head around this, if we look at the picture of the rectangular antenna you posted above, how do we work out itâs length? Do we measure the lengths of the segments up to the bend? Is it all one length regardless of shape? Getting picky, where do we start and stop the measurement? Does it include the bit of coat-hanger under the screws? Does it include the screws? What about the wires on the adapter to connect it to co-axe?
I told you I never did manage to understand this stuff, right?
The loop antenna or the folded dipole is all one length regardless of shape. What I didnât mention is that the thickness of the wire or tube adds somewhat to the size. A thicker wire means less length needed.
Yes typically the length includes the portion of wire under the screws (eg. the whisker V shape bend of a bowtie antenna).
The wires on the balun connecting the antenna to the coax are an interesting case. A friend of mine wasnât getting good reception and in trying to track down the problem, shortened the wires on the balun he had bought by three inches. Suddenly his reception perked up!
Iâm not sure antenna design and building is about necessarily âunderstandingâ fully the electromagnetic spectrum and its measurements. With me itâs a lot of trial and error trying to stay within the ballpark of the proposed measures and guidelines. Also there is so much variability in day to day reception. Iâve seen swings of up to 20% in reception on certain days due to atmospheric conditions so that precise antenna measurements are not that significant
You mentioned the 128" size wound up into a helical shape. Fractal antennas currently interest me (Iâm building one as a test and experiment) because of their use of wire lengths, shapes and patterns.
Well, I cut my circle down to 64 inches and it seems to measure about 22 diameter. I tried it again, with $15 booster from Walmart and picked up 3 UHF channels. Finally took it outside of my Faraday cage (I think walls have lead paint) and got 15 UHF but not channel 11, which is the only one I need. I added a 34 x 27 inch reflector of cardboard covered with tin foil and finally got channel 11.
I live 30 miles from the towers but I am building this for my nieces apartment which is 50 miles from the same tower. Hopefully this this will work down there too.
Funny, I didnât expect to get all the UHF channels and could have saved $70 on buying the antenna if this works down there.
I would try it at her place by itself without joining the loop to the Winegard. Loop to Winegard booster to Tablo. Then if channel 11 comes in OK, combine the two (unless the loop gets the UHF channels as well as the Winegard).
BTW those $15 boosters may do more harm than good! They are inexpensive because their circuitry has high noise figures (NF) that actually can degrade reception. Her Winegard booster will have a much lower NF than the Walmart one.
Thanks, I figured the Walmart one wasnt great and the Winegard will be the one I use when I try it out this weekend. Now I just have to build the PVC framework to hold it.
I used 3 sheets of tin foil to cover the cardboard and taped the ends. Will it hurt the signal if I run a piece of masking tape between each tin foil piece to keep it from ripping easily? I am guessing not but figured I would ask first.
If the masking tape isnât an insulator⌠I have a tin foil\cardboard reflector on one of my antennas and I used metallic duct tape from Home Depot to join all the aluminum foil rolls together. But that adds another $7 to the bill. I should have mentioned that my wife buys the heavy duty aluminum foil for her cooking and that is quite sturdy (more so than the regular stuff) which is what I used. Another reflector that I used was one of her old cooking racks! BTW most people donât realize that a lot of these high priced antennas can be made from pie plates. Eat the pie and save the plate (google pietenna). Here is a video of somebody who did a double take when he opened up a Clearstream antenna to see what was inside:
@MarkKindle - So I was thinking, since I have been doing all of this just to try and get Channel 11 on Hi-VHF, if I just put the reflector behind the store bought Winegard Flatwave Air antenna, it should increase the signal I am currrently getting right? I donât have a signal tester but when I was doing channel scans I could sometimes get 3 Orange circles on the Tablo scan.
I am heading down to my nieces Sunday AM to try this all out and see if I can finally get her a signal on channel 11. I will share results tomorrow after I am done.
I donât know if the Winegard has its own internal reflector. However it wonât hurt to try to place your own reflector behind it. VHF reflectors are usually 9 to 16 inches behind the antenna elements so you can try it at different distances. In fact the bigger the reflector the more gain.
A certain type of reflector is a three sided one - a back side with two flaps left and right sort of like the ones you see at the beach people use who are sun tanning their face. This one forms a cup around the antenna reflecting the signal into it from three angles.
There are even trough reflectors - they extend under and above the antenna. The same way the left and right flaps would. On my loop in the attic, I have a reflector that has both left and right flaps and over and above ones: all of these form a cup shape around the antenna to reflect the signal into it from 5 different angles. That setup gets me PBS at 100% and NBC at 90. This reflector setup nets me an additional 20% in signal strength than without it.
The best antenna ever made - the CM 4251 had a circular cup shaped reflector around it. It worked mostly through its reflector. In fact thatâs the principle behind satellite dishes.
With the Gray Hoverman antenna one has NARODS which are VHF length rods placed a half an inch from the antenna. They are not joined to the antenna, just close to it (under and above it). They receive VHF signals and by induction transfer them to the GH. You can try the same with the Winegard by putting it in the loop and see if that induces a higher VHF signal in the Winegard.
Good luck with your efforts Sunday. Bring lots of cardboard and a large roll of tin foil⌠One day my wife asked me, âHey I had a big roll of tin foil here, where did it go?â
I checked out the Winegard and it has an internal reflector - 4 rods adequate for UHF. I would still try the additional reflector for VHF.
Google âantenna trough reflectorâ and go to the images section of the returned results. Youâll see a variety of reflector shapes to surround the Winegard.
Well, I tried out the circle antenna and reflector today and it didnât work well at all. Actually when when I connected both the Winegard and the Circle antenna to a 1x2 reversed coax splitter, my signal got worse and I could only get 3 channels.
After more than an hour of messing with stuff, we ended up using a 2x4 and bungeecords and strapped the Winegard to the porch post outside and ran the cable inside and was able to get Fox in prefectly with 5 Green dots. All channels except for WCWF-14 which is a UHF station was received (Flash/Arrow etcâŚ).
Someone better with antennas may be able to get it to work inside but I am pretty much at the end of my experimenting. Hopefully that labdlord will allow us to mount the antenna directly to the 4x4 post and not use bungees but if not I think this is my only option.
Thanks to all for the responses and assistance, especially @MarkKindle for his numerous responses and quality info.
Itâs possible to sit a 6 or 10 foot yagi on a chair inside a residence and point a window from inside a residence but do not expect spousal approval if you try it.
