[Wavess]

I´m trying to make a vertical bazooka antenna for my AWM631tx and save some grams on it. This is basically done by a piece of coax cable and heatshrink tube, but I´m bit confused on the dimensions that I have to give.
Here
http://www.rc-cam.co...htm#rc-cam4_top

he starts with a 8" cable and ends up with 5.2"

On this manual
http://www.iw5edi.co...bazooka-antenna,18

if I take the first formula for calculating the overal lenght it gives me:

L=15000/2450= 6.12cm (2.40")

I have also noticed that on the fatshark 10mW 2.4tx the overal antenna lenght is about 2.8 cm (1.10")

Which way to go?

[Mr.RC-Cam]

Quote

he starts with a 8" cable and ends up with 5.2"

I started with a long piece to allow for easier turtle-necking. The final length of 5.2 inches is what it ended up as after I soldered it to the X10 transmitter. I mentioned the installed length in the article because the feedline length can make a difference at these frequencies due to matching trickery; the 5.2 inches worked well for my X10 hack.

Quote

if I take the first formula for calculating the overal lenght it gives me:
L=15000/2450= 6.12cm (2.40")

That appears to be 1/2 wavelength in free air. You will need to account for the metallic medium's velocity factor which causes the lengths to be shorter.

The elements need to be 1/4 wave long and corrected for velocity factory. Generally speaking, the exposed driven element will probably be 4% shorter (approximation). The counterpoise (coax shield) element length will usually be shorter than that since the velocity factor of coax is different (varies on coax type).

For the X10 project I kept things simple and the described lengths worked well for that particular transmitter and coax choice. The goal was to keep it simple and concise so other X10 Tx hackers could duplicate it.

In a perfect world you would probably start by making the lengths 5% longer than necessary and then trim them using a microwave network analyzer to find the best matching. Without the correct measuring tools, building microwave antennas is mostly painful trial and error.

Quote

I have also noticed that on the fatshark 10mW 2.4tx the overal antenna lenght is about 2.8 cm (1.10")

That would indicate it is a very simple 1/4 wave monopole, which are sometimes the lowest performance choices for these applications. The length you found may be what offered the best performance for the characterized performance of their Tx's design, or could simply indicate sloppy cut length. You decide.

[Wavess]

Thanks MR.RC-Cam valuable info as always.
The link I posted before didn´t show the manual I found, let´s try again:
Vertical Bazooka Manual

they do take acount about the vf, I think it´s well explained and things that you have explained are followed there.

I think I´ll go straight forward with it, What do you think?

[Mr.RC-Cam]

Thanks for fixing the link. The link's instructions are easy enough to follow. Keep in mind that their driven element is extra long and they expect you to trim the length for proper match. Their operating frequencies were much lower, so everything was less critical. At microwave frequencies, everything matters.

So without test gear you have to make educated guesses at what the best length for the driven element should be, then hope for the best. Range testing will only find the badly constructed antennas, but is better than nothing.

How about this: Build the rc-cam version, then build one per the link you gave. Then report what you find. I have a feeling they will offer the same performance in your application. Or maybe not.

[Wavess]

Mr.RC-Cam, on 13 November 2009 - 10:38 PM, said:

Thanks for fixing the link. The link's instructions are easy enough to follow. Keep in mind that their driven element is extra long and they expect you to trim the length for proper match. Their operating frequencies were much lower, so everything was less critical. At microwave frequencies, everything matters.

So without test gear you have to make educated guesses at what the best length for the driven element should be, then hope for the best. Range testing will only find the badly constructed antennas, but is better than nothing.

How about this: Build the rc-cam version, then build one per the link you gave. Then report what you find. I have a feeling they will offer the same performance in your application. Or maybe not.

Sure that would be the best, I will build the two options and report back my conclutions.

[Wavess]

Well soldered and installed the first bazooka Antenna, in this case the first it´s the rc-cam version, a little bit tricky to place the braid over the coax jacket, but done. What I´m thinking is about the strenght of the cable itself just holding in site with 3 soldered points. The thing stands very well but don´t know if in a bad landing or with the wind pushing back constantly this would be a weak point. Maybe would hot glue the join point but taking care that the glue does not touch the antenna conductor or the rf side pad. Here it´s a pic of it, my cam does not like very much the Macro style though.

This post has been edited by Wavess: 14 November 2009 - 02:56 PM

[Wavess]

Tried the vertical bazooka and the results are not bad at all, but seems that better performance is obtained with a sma conector and a 3db whip.
The only bad thing of all this is that the only the solder points (ground) are holding the antenna in place. I have physically tied to a plastic vertical pushrod but even that I noticed yesterday that I loose video at about 25m.

On a close inspection 1 ground leg was unsoldered and the rf line too, lifting a little bit of the airwave pad, lucky that it was only a part of a pad. Now I have secured cable antenna with airwave module with hot glue, a little portion of it is touching the rf line, would I notice this on the performance?.

[Mr.RC-Cam]

Quote

but seems that better performance is obtained with a sma conector and a 3db whip.

There all sorts of designs that I see builders call "whips", so some details would be grand; Monopole, dipole, .. vertical, ground plane, ... 1/4 wave, 1/2 wave, ... etc.

Quote

Now I have secured cable antenna with airwave module with hot glue, ..., would I notice this on the performance?.

Doubtful, unless you notice a change in performance.

[Wavess]

Mr.RC-Cam, on 21 December 2009 - 11:34 PM, said:

There all sorts of designs that I see builders call "whips", so some details would be grand; Monopole, dipole, .. vertical, ground plane, ... 1/4 wave, 1/2 wave, ... etc.


Doubtful, unless you notice a change in performance.

Sorry I meant a comercial 3db rubber duck omnidirectional, dipole