Electronics > RF, Microwave, Ham Radio

Acquired a free Yagi, have a few n00b questions.

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rwgast_lowlevellogicdesin:
So I got a pretty nice Yagi for free, a Larid 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?

AF6LJ:
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.

German_EE:
So many questions  :) Let'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

rwgast_lowlevellogicdesin:
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.

LabSpokane:
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.

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