Acquired a free Yagi, have a few n00b questions. - Page 1
Forum section: electronics / rf-microwave

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: May 15, 2016, 07:14:47 pm
content: So I got a pretty nice Yagi for free, aLarid Y4505.-0http://www.wpsantennas.com/y4505-antenexprofessionalgradegoldanodized450-470mhz5element92dbdyagiantenna.aspxiIve actually never used a yagi before, this one is listed for use from 450-470mhz. Well I did a little googling and I don't see to much interesting in 450-470. I think some the family radio system stuff, is in that frequency range but it seems thats about it. If anyone knows of anything cool between 450 and 470 let me know, Im hoping I can at least find some sat down links in this range.My real question is how good will this thing work at other frequency's? I am really interested in the 433 ISM band which is pretty close to 450, would this yagi work better for a long range 433 link than some kind of home brewed col linear or cantenna? I read the data sheet I would have thought it would have listed how much DB drop off per decade or something but no such luck.Also whats the deal with the number of elements, this is a 5 element, why not a 3 or a 10 element? I know the back element is always the reflector but and then you have the main element cut to wavelength, but other than that how does the amount of elements effect things?

author: AF6LJ
author_rank: Unknown
timestamp: May 15, 2016, 07:19:46 pm
content: Well here in the People's Republic of Kalifornia there isn't much worth listening on 450-470MHZ.The antenna will work on the 440MHZ amateur band with somewhat less performance.All the elements are too short and closely spaced together, (by about ten percent give or take.) for amateur use.

author: German_EE
author_rank: Super Contributor
timestamp: May 15, 2016, 07:33:16 pm
content: So many questionsLet's see if I can help:My real question is how good will this thing work at other frequency's?Not very well. The idea is that an antenna resonates over a narrow range of frequencies and as you move outside of that range SWR increases and receive losses mount.Would this yagi work better for a long range 433 link than some kind of home brewed collinear or cantenna?Yes, after it has been retuned to the 433 MHz band by increasing the length of the elements. A collinear will radiate your signal equally in all directions and is therefore not so good for long distance whilst a cantenna is normally used for microwave or wifi signals.What's the deal with the number of elements, this is a 5 element, why not a 3 or a 10 element? I know the back element is always the reflector but and then you have the main element cut to wavelength, but other than that how does the amount of elements effect things?The greater the number of elements the more power is pushed out in a forward direction compared with a simple dipole, this is normally given as a FORWARD GAIN figure along with the FRONT TO BACK RATIO. As you add elements both gain and front to back ratio increase. Note that all elements in a beam antenna are cut to length according to the frequency of use

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: May 15, 2016, 10:00:45 pm
content: Well as stated above there isn't anything going on in 450-470.... Sad its a nice yagi gold plated and all, and seems pricey.. I could sell it but who the heck needs a yagi tuned to the 450 band?How would one go about retuning it to 433/440?? The fluff says it has some kind of internl matching network will that cause any issues if retuned? I want to slap this think on a pole and scatter 433 trancivers around then make contact with them, or find intresting gear running in the ISM band that may be demodulated with gnu radio.I like the antenna its just a crappy range and im not sure how to retune the thing, im sure ill have to do mechanical modifications but in not even sure the best way to work with the gold plated tube.What in the heck could this guy have originally been used for, its passed around but originally came from a lone poll near a park from what I understand not sure though.

author: LabSpokane
author_rank: Super Contributor
timestamp: May 15, 2016, 10:59:43 pm
content: Just eBay it. It's a $130 antenna and whatever you get could be put to better use in a usable band.450-470 is also used for telemetry in very frequency congested areas. It stinks if you have to use it because the range is limited as compared to the lower bands. And with 9dB of gain, you'll pretty well need to point it at what you want to hear. You might get some juicy data from your local wastewater pumping station if you're lucky.

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 15, 2016, 11:20:35 pm
content: $230? what a rip off, build your own...

author: LabSpokane
author_rank: Super Contributor
timestamp: May 16, 2016, 12:44:38 am
content: Quote from: Mechatrommer on May 15, 2016, 11:20:35 pmIt's $130, not 260. At least that would be my price to buy it. It's a commercial antenna, designed to be put in place and left for a decade or more. The radio it plugs into is typically $1500-2000, so a $130 antenna is the least of it.

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 16, 2016, 03:45:39 am
content: Quote from: LabSpokane on May 16, 2016, 12:44:38 amit looks like $230 from here...http://www.wpsantennas.com/y4505-antenexprofessionalgradegoldanodized450-470mhz5element92dbdyagiantenna.aspxiron is made to last no matter how many rust it has. i built 2.1GHz yagi few years back, put some meters away coax to SMA connection. $50 if i'm not mistaken the cost, with many meters of coax left as spared and few SMAs for stock. still looks like when it was made, except some scratches on the painting. decommissioned (but still kept) because i dont use broadband mobile anymore... many variant on how to diy a yagi in the net, fwiw...

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: May 16, 2016, 07:16:04 am
content: Well the antenna is exspensive and I have thought about selling it, but it is also very nice. I think id much rather modify it. I would like to connect it to an amplifier and pi with SDR dongle in a remote location on a mountain behind my house. I have a lot of ideas for it. I think maybe scattering around 434mhz cheapo sparkfun transmitters could be cool, maybe even using it for com with a bot or drone at long distances. So what kind of software would help me figure out the lengths to make the elements work well on 434 ISM. It would be even nicer if I could modify it in a way where I could modify back and forth for any frequency between 400-500mhz. Besides even if I wanted to sell the thing who would be looking for an expensive antenna on e-bay in a mostly useless band? Its spendy becuase as mentioned its meant to last and its gold plated, im sure anyone looking for that would be a professional buying it new.Lastly and a bit off note is there a way to make home made coax relays, or use solid state parts to switch antennas and filters in and out? Last time I looked at coax relays they were pretty pricey if I remember right they were 20 to 50 a pop. I need a much cheaper way of switching antennas remotely, all the equipment will be quite a vertical hike away controlled via wifi, I dont mind making the hike to retune antennas sometime but not every time I need a different filter and antenna swamped in. I plan on on dealing with frequency's from 80m to 1700mhz iridium stuff.

author: LabSpokane
author_rank: Super Contributor
timestamp: May 16, 2016, 08:47:49 am
content: It's gold anodized, not gold plated.And it's a directional antenna, designed for point to point, at least points in maybe a 60 degree sector. I haven't pulled up the data sheet, but the 3dB beam width is certainly no more than 90 deg. If you want to "scatter" radios, you need an omni.

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: May 16, 2016, 09:15:17 am
content: hence the rotor, this should let me scan for signals. Is there no good way to hack this thing up to work at different frequencys

author: Delta
author_rank: Super Contributor
timestamp: May 16, 2016, 09:56:45 am
content: Have you even gone as far as reading the Wikipedia article on Yagi Uda antennas?

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 16, 2016, 10:40:02 am
content: Quote from: rwgast_lowlevellogicdesin on May 16, 2016, 09:15:17 amno, esp the pricey gold plated plated... you cut the elements to increase freq, add to it to decrease, but then there is distance between elements... my suggestion just leave the gold plated plated be until someone interested in it... read this KK6WKK...http://www.skyscan.ca/Antennas.htm

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: May 16, 2016, 05:23:19 pm
content: Thanks for the link, i have read the wiki on yaggi a while ago. I just never needed to use one, I usually homebrew all my antennas and either use omni's or directional antennas using cans/dishes.I realize one would have to cut the elements to increase frequency, or add to the elements in order to decrease the frequency. I was thinking maybe one could cut the original elements down to 400mhz and the slide a length of copper pipe up the element to get between 500 to 400mhz. The one thing I don't know anything about is the spacing which im guessing the article will explain. I guess I just assumed the yagi was optimized for 450, so to be able to "tune" the elements with copper pipe from 400 to 500 shouldn't have made any kind of huge difference. But im guessing that I am wrong and thats what I get for assuming? I mean this thing would be a cool antenna if it could be made to work at 70cm.

author: madalf71
author_rank: Contributor
timestamp: May 17, 2016, 06:51:25 am
content: Might want to get yourself a RSGB or ARRL handbook, very helpful.

author: shawnb
author_rank: Contributor
timestamp: May 18, 2016, 09:08:05 pm
content: You would need to increase both the length of the elements and the spacing between elements to retune to 430 MHz. They are small differences (probably <3/4" for element lengths and <1/3" to <2" for spacing, each element/spacing with its own differences) but they make enough difference to justify Laird separately manufacturing the Y4305 for 430-450 MHz. Adjusting the spacing is an issue since the elements are welded in place. Not really practical to try and build a Yagi to retune 400-500 MHz on the fly with that many moving parts and relatively small tolerances.You would be better off building a yagi from scratch. If you're looking to keep it cheap and easy, research Quagi online and try one of those. You'd get far better performance from a wood boom and some welding rods than hacking a Frankentenna.