Retuning an AXR--RF

DHawthorne

I have an AXR-RF that's not paired with any transmitter devices I have on hand, and was wondering if I was looking for trouble thinking to re-tune it myself. It looks like there is a simple variable choke on the RF board that simply needs to be tweaked - I could, conceivably, just hold down a button on the transmitter I want to use and adjust it until I got a signal.

Questions are, is that choke all there is to it, and how far from the stated frequency can it be adjusted? Or am I completely off base and should just bite the bullet and stop trying to be a cheapskate?

Thomas Hayes

Hi DHawthorne
Depending on the choke size I doubt that you will be able to adjust it that much from the centre frequency that the circiut is designed for. There must be a osc. in the circuit that is used to set the operating circuit frequency. I haven't looked at the box (I have 1 at home that I will take a look at) and see if you can modify the RF freq. I would not do any adjustment to far though, as you might end up with a dead box. What freq is the present box and what are you trying to get?

DHawthorne

I'm trying to go from 304 MHz to 407MHz. Looking at the RF board, I don't see anything in the way of crystals or anything but that adjustable choke to determine the frequency, just generic IC's and transitors.

Thomas Hayes

Hi Dave
I haven't opened my box yet, but I think I have the same one. Do you have a freq. counter or scope with one built in. If so you could check the freq. at the choke, they try adjusting it to where you want. I assume that you have a couple of devices at the 407 Mhz range to use to test the box. You may have to be careful that the test probes don't add load to the circuit and give you a false reading. Like I said I have one at home that I use for an old softkey to control my home system, I will try to open it this weekend.

veraview

I just retuned an AXR-RF from 304 Mhz to 315Mhz to match up with a new transmitter. This was an older AXR-RF (1994) which was very easy to tune... from my conversation with tech support I gathered that later models are more difficult.

There are two test points on the board to hook up a 'scope, but they are unlabeled. AMX tech support was kind enough to fax me a drawing that showed where they are and how to tune.

There is a tech note to identify your receiver, and what its tunable range is:

http://www.amx.com/techsupport/PDNTechNote.asp?id=340

Thomas Hayes

Hi Veraview
You wouldn't still have a copy of that circuit laying around? I checked that tech note and I think I maybe able to use a second RF reciever I have to work with my 4 button hand held(can't have enough toys and remotes around the home). Okay Dave, back to you now. I took my RF box a part tonight and its a pretty simple circuit(like you said), check out the tech note that veraview sent. As a personel rule of thumb I usually mark the orginal point and count the number/direction of turns. You should also use a non-inductive screw driver to prevent a false reading.

DHawthorne

That is exactly the information I was looking for - sadly, my receiver is not capable of being retuned to the frequency I need. It's good information to know, however.

veraview

Here ya go...