Yagi Questions

Hello All. I recently built a 10 element 850Mhz yagi antenna: https://goo.gl/photos/gZojPF8eThPxLsQF6

I used this site for the measurements: Martin E. Meserve - K7MEM - VHF/UHF Yagi Antenna Design
I also used the feeding method on the same page (1/2 wavelength of coax bridge on the folded dipole).


The reason I built the antenna was to try to block out some interference from several simulcast towers. I was hoping a directional antenna would help me isolate a single tower. That didn't happen for geographic reasons... but that's another thread.

Otherwise it seems to work pretty well, if I pan it around in the direction of a control tower, I get very strong reception within about 15-20deg.

I have just a couple of questions:

How accurate does the positioning of the parasitic elements need to be? I'm sure the spacing is exact to within 1-2mm, but the elements aren't exactly square to each other. They are also slighly skewed in the vertical plane (horizontal in the picture). What kind of tolerance should I be shooting for here?

How can I quantitatively test the performance of the antenna? Right now I'm just panning it around and watching what happens in SDR#. It would be nice to have real data to see if my tweaking is making the situation better or worse.

Looks awesome I want to build one like that one day

I had a similar problem, however I wanted to monitor a second system on UHF. My resolve was to run my discone into a bandpass filter and combiner. This blocked the stronger 800 mhz signal from the discone. On the second port of the combiner I simply made a 1/4 wave antenna cut to the control channel (~3.25") Using the 1/4 wave I no longer had the overload problem from multiple sites. Its been working great.

Question 1....as it is for receive only, you should be fine with a bit of lean, bend, whatever. The build looks great by the way.

Question 2...to quantify your build, use the constant control freq as a source. If you know the location of the tower, then point the antenna right at the source...then as you did, pan it a few degrees one side and then the other and determine how much the signal drops...you are figuring its beamwidth. . It is dependent also on how far the transmitter is from you...a beam is like throwing a handful of sand...it widens as it gets further away. LIke a shotgun blast. Also find the point of strongest reception, and then turn the antenna 180 degrees away. You are then measure front to back ratio...its ability to attenuate signals from the rear.

good luck and have fun...the best part of building antennas is experimenting....

Druhe,

Can you tell me the model number of your bandpass filter? I've been looking high and low for what you've got. Where did you get it?


Sent from my iPhone using Tapatalk

AnikF1R said:

Druhe,

Can you tell me the model number of your bandpass filter? I've been looking high and low for what you've got. Where did you get it?


Sent from my iPhone using Tapatalk

Click to expand...

The low pass filter is made by Crystaltek and was purchased from DigiKey. Here ya go

CLPFL Series Low Pass Filters - Crystek | DigiKey

Let us know how it works out

Thanks druhe! I'll let you know what I find out.

I tried sending a PM. I don't think I did it right...

Druhe, what frequency filter did you use? It almost looks like the 700 and 800 MHz models don't begin significantly attenuating until well into the GHz range.

Thanks for helping with this!

AnikF1R said:

I tried sending a PM. I don't think I did it right...

Druhe, what frequency filter did you use? It almost looks like the 700 and 800 MHz models don't begin significantly attenuating until well into the GHz range.

Thanks for helping with this!

Click to expand...

I'm using the CLPFL-0700

Nice Build good looking Antenna.......

I got my low pass filter the other day. Unfortunately, my results were unsatisfactory. I have a quarter wave ground plane cut for the air band. This goes through the filter and gets combined with an 850 MHz antenna. I ended up losing too much signal with the air band antenna going through the splitter. Plus, the 850 stuff was still coming in choppy. This isn't surprising since combining two antennas for one scanner rarely goes as planned.

I'll continue to experiment, so this is far from over