Cactus Mod - Antenna Extension?

danman281 · Nov 28, 2008

So far I have found two websites concerning this mod:

Both of them have good write ups, however something doesn't make sense. In the first website, they said to solder on the "antanna" onto the bottom left corner. On the second website, they soldered it onto the bottom right(next to the battery). When I soldered it on the bottom left with a simple coiled wire, it didn't work (lost distance actually). See figure a1 below.

figure 1a - my attempt

I decided to take it off since it didn't do anything. Btw... was that circuit important? Did I damage it by any chance? It still works...

Normally, the cactus is really inconsistent after a few feet away. Even from ten feet it may miss 1/10 tries or more. With the DIY (from the first link) loop wire antenna, I lost range. This may be because thats not how antennas work (at least from how I learned) OR it's not the correct antenna circuit. I then held the same wire on the other circuit and tested roughly 100 feet away and it worked (somewhat). When I took it off, it no longer worked. This must mean that the bottom right circuit is for the antenna. Can someone still confirm this please?

Dweller · Nov 28, 2008

From what I have read, either spot should work, but some people seem to have better luck with the hole next to C3.

How long of a wire are you using?

dEARlEADER · Nov 28, 2008

(watching thread)

I have yet to mod my triggers. Why doesn't gadget infinity just add a small antenna to their triggers? The small increase in cost would allow them some pretty impressive range bragging.

Big Mike · Nov 28, 2008

Why doesn't gadget infinity just add a small antenna to their triggers? The small increase in cost would allow them some pretty impressive range bragging.

They don't make them, they just sell them. It would be cost prohibitive to do the mod themselves.

danman281 · Nov 28, 2008

Guys, I'm having trouble with the consistency. Most of them time, even ten feet away I don't get anything. It will work 99 percent of the time if I have it within 1.3 feet. After that it drops exponentially. It barely works at 7 feet. I read someone else's post that their cactus trigger goes beyond 100 feet with no mod.

I ran another quick test. I walked aprox 10-15 feet where it normally wouldn't work. I then used the makeshift wired antenna towards the circuit and it worked but inconsistently. This means that the antenna circuit must be helping a little...

How well does everyone else's cactus work without the mod? I doubt these things come out of the box this crappy

Big Mike · Nov 28, 2008

Have you tried putting in a fresh battery?

dEARlEADER · Nov 28, 2008

Have you replaced the batteries as suggested by many?

danman281 · Nov 28, 2008

I got this in the mail today and the batteries were brand new. Should I buy new batteries anyways?

To answer Dweller's question: The length of the wire I used was roughly 12'' coiled up

Big Mike · Nov 28, 2008

I got this in the mail today and the batteries were brand new. Should I buy new batteries anyways?

Those batteries might have been sitting there for a long, long time. This is a budget product, it wouldn't be uncommon to get old 'nearly dead' batteries.

danman281 · Nov 28, 2008

I checked both batteries using a multimeter.

The Receiver uses: CR2 3V Alkaline Battery
The multimeter read: 3.2 V (good)

The Transmitter uses: L1028 12V 23A Battery
The multimeter read: 12.2 V (good)

The batteries seems to still be in working order.

Was it possible that the first soldering job damaged the circuit board? I don't see how thats possible though. Even if I did, the other antenna circuit is still there. Any electrical engineers in this forum? lol

tirediron · Nov 28, 2008

I don't know what frequency the cacti operate on; the link refers to an AE 12.39 inches long. Has anyone double-checked the math to ensure that that's a full fraction of the wavelength?

Dweller · Nov 28, 2008

tirediron said:
I don't know what frequency the cacti operate on; the link refers to an AE 12.39 inches long. Has anyone double-checked the math to ensure that that's a full fraction of the wavelength?

I can not vouch for the accuracy of this comment, but here a user comment states:

Hmmm.
The length of an antenna is fairly critical to get maximum efficiency.
If it's the wrong length then most of the transmitted power can be reflected back down into the transmitter.
So theoretically any added antenna needs to be approximately the correct length.
Calculations will give the full wavelength of a device operating at 433 MHz at around 665 mm or just over half a meter. But most antennas are not full wave (too long) and are a fraction of that. 1/4 wave being the most common. This then equals 166 mm (16.6) cm which is still too long so going for a 1/8 wavelength we get 8 cm for maximum efficiency. 1 or 2 cms either side can drastically reduce performance. So there you go. And a thick solid copper (or aluminium) wire would be better than multistrand.
I'm about to try it myself.

edited to add:

According to this site the proper length for 433Mhz should be 12.97 inches for 1/2 wave and 6.48 inches for quarter, so it sounds like the antenna may be a bit short. I do not know if its enough to cause a problem but its something to consider.

tirediron · Nov 28, 2008

Dweller said:
I can not vouch for the accuracy of this comment, but here a user comment states:

edited to add:

According to this site the proper length for 433Mhz should be 12.97 inches for 1/2 wave and 6.48 inches for quarter, so it sounds like the antenna may be a bit short. I do not know if its enough to cause a problem but its something to consider.

At those frequencies? Definitely, a difference of half an inch could potentially be the difference between go and no-go. Of course I suspect that the quality of the Tx and Rx components aren't the best, but it can't hurt to make the Ae as accurate as possible.

danman281 · Nov 28, 2008

tirediron said:
I don't know what frequency the cacti operate on; the link refers to an AE 12.39 inches long. Has anyone double-checked the math to ensure that that's a full fraction of the wavelength?

The Cactus Operates at 433 Mhz. It sounds about right to me but the person was just a tad bit off.

Whats weird is that even after I took off the antenna, the problem persisted. I had trouble getting a signal just ten feet away. I'm really starting to think it is broken

Dweller said:
I can not vouch for the accuracy of this comment, but here a user comment states:

edited to add:

According to this site the proper length for 433Mhz should be 12.97 inches for 1/2 wave and 6.48 inches for quarter, so it sounds like the antenna may be a bit short. I do not know if its enough to cause a problem but its something to consider.

That looks about right. Hmm.. Does curling the wire into a coil chance the affect by any chance?

Also, why the heck is there two antenna circuits on the V2 Transmitter?

danman281 · Nov 29, 2008

Good news!

I just tested my transmitter with a 6 - 1/4'' wire from a cat-5 cable. I left the wire straight (uncoiled) and touching the bottom right antenna circuit. Response was very consistent and range definitely increased. I was actually able to do the minimum "30 feet" in my house. When I took it off, they no longer worked.

I'm going to buy a real antenna and mount it for good. I will keep you guys updated when it comes in.