VHF Yagi Project

Hello,
Here are a couple pics of my VHF Yagi project.
I am building it for 185 MHZ, using an old TV antenna.
The donor antenna had insulated plastic brackets for the
elements, so I was going to use one to insulate the folded
dipole element. The elements are 3/8" diameter. I am going to
attempt to receive HI VHF towers about 80 miles away. Here are
a couple of pics. Special thanks to Fringe Reception for helping me
out. When it's done it will have 8 elements, the parasitic elements
will be bonded to the boom.

John

Cool project. Just curious, what's the determining factor behind the number of elements being 8 in your case.

Originally Posted by Aaron62

Cool project. Just curious, what's the determining factor behind the number of elements being 8 in your case.

The antenna calculator I used calculated 8 elements based on gain and frequency.
If you increase the gain, there will be more elements on a longer boom. The donor
antenna boom was not long enough to allow for any more elements or gain.

John

Originally Posted by jlguler

The donor antenna boom was not long enough to allow for any more elements or gain.

John

That's the same reason my Project-9 antenna is limited to its length. Works for meeee...

Jim

I put the antenna together tonight... In our upstairs bedroom it was picking
up Madison UHF stations 56 miles away (the same channels we receive with the 4228)
It is supposed to be warm here tomorrow so I should be able to get it on the roof and
see what it will do!! I took pics of the assembly, will post them soon..... If I cannot receive
Chicago, I will move it around and see what happens!!

John

I did not get a chance to get the antenna up today. Will have to wait for the
next warm day. Here are a few pics of the assembly. I checked the connections
with and ohmeter, all is good electrically.

JohnP1050607.jpgP1050608.jpgP1060609.jpgP1060610.jpgP1060611.jpg

John,

Good job!

Two pointers: in photo 1, I suggest you use a Scotchbrite pad or something similar to eliminate the orange iron oxide (rust) deposits on the plastic support for your driven element (dipole). That deposit could carry current or be capacitive and change your antenna's impedence which results in signal loss do to VSWR ... especially when its wet from rain.

Secondly, unless you have future plans to extend the boom length to add more elements, I would cut the extra material away.

Be aware, to add more elements you will have to relocate every element by a tiny distance: you would have to start from scratch and rotate the boom and its extension 90 degrees. The boom would be considerably weakened. I'd cut it.

Jim

I installed the antenna today. We now pick up 35 WWTO out of Lassale, IL
72 miles away. Oddly, the scan also found 6.1 and 6.2 which is WITI out of
Milwaukee. The antenna is pointed SE, not sure why channel 6 showed up.
6.1 and 6.2 are not watchable, too weak, but they showed up in the scan.
They must have a powerful transmitter. Tomorrow I am going to point it towards
Milwaukee/Madison and see if I pick up any channels. It's mounted with the 4228,
I put it about two feet under the 4228. We still have our original channels, so I don't
think the yagi is interfering with the 4228. I did clean up the rust spots and cut the boom
down as Fringe Reception suggested. Very promising so far!!!!

John

John, WOOHOO!

Now, I suggest you try the pair at different heights. A few inches up OR down can make major differences in UHF reception. VHF usually requires more than inches in height changes and as you know, height is usually beneficial for both VHF and UHF.

As far as antenna seperation "by the book" they should be farther away from each other but if what you have works ... forget the book! I call myself an Imagineer and would never refer to myself as a (limited) Engineer. OTA reception is a bit of a black-art: what should work often does not and what does work sometimes makes little sense.

Jim

I pointed the yagi towards Milwaukee today, gained ten channels. A couple
of them are only 25-30% signal, so reception is spotty. A couple of the extra
channels are 45-50% signal, not too bad for towers 80 miles away!! I think I need
to:
1) Lengthen the antenna for more gain (or)
2) Replace the single dipole with a folded dipole (if that would increase gain) (or)
3) Now that I know I can get Milwaukee, buy an Antennacraft Y-10-7-13

We still receive all of the original channels we received with the 4228.
The yagi added a total of ten channels, five network and alternates, and
five religious channels (trinity broadcasting)

John

Here is a pic of the installation and a pic of 6.2, one of
the Milwaukee stations we receive. The signal is not always
consistent, it cuts out from time to time. I may increase the
gain on the antenna to see if that helps. It could be interference
between here and the tower, so I may never get a solid signal
on these stations...... But I'm still going to try!!!!P1090612.jpgP1090613.jpg