Can URC provide the frequencies the MRF responds to?

Sites that sell cores identify the frequencies that are attenuated for each model core they sell. The site I referenced above has a search feature that includes the attenuated frequency/frequencies as a search criteria.

I suspect that fine tuning of the ferrite is splitting hairs. You just want one that is effective above about 1MHZ. The emitter signals are below that. Any core of reasonable size (not so large that it is unreasonable) should be sufficient above that frequency. Keep the outer diameter to less than the size of a lifesaver. Inner diameter big enough to fit the connector plus 1 or 2 runs of the emitter cable. About an inch long or less.

The ones I used were:
OD = 12.5mm
ID = 7.8mm
Length = 6.3mm
This is more of a torroid shape. Looks like a little tire from a matchbox car.

The RF band used by the MX-850 and MRF units is 418MHZ. This band used to be relatively free from interference. But nowadays a lot of low power devices may be operating there (other home automation devices, x10 devices, consumer weather stations/remote temperature units, and so forth). Another possible candidate is RF interference on 2nd or 3rd order harmonics from radio transmissions at 1/2 or 1/4th that frequency. 1/4th of 418mhz is in the top end of the FM radio band. There could easily be interference from there that is actually interfering in the 418mhz range.

My guess is that URC's answer has been to "tune" their RF receivers to a very high "q" circuit that effectively narrows the frequency range it recognizes. It looks like their marketing group decided to coin it "narrow band". If you do that, you could actually reduce the overall gain & sensitivity of the reciever to more effectively shut out adjacent frequencies. To design a more robust RF signaling protocol (such as those being used for computer WiFI 802.11a/b/g) would have been too expensive.

I still think including a couple bucks worth of ferrites in their MRF kits would have been a stellar idea that could have prevented a lot of unnecessary warranty returns. Hopefully they will show some hindsight.

I only have an MRF250 and MX-850 remote, so I can't speak for the other products. But I suspect all the URC RF-capable remotes work in the 418MHZ band.

Bought my cores today and installed them.

It has improved the responsiveness of the remote system. Before I was having occasional and intermittent problems with response even though the LED didnt indicate any RFI on channel 0.

Now the system seems to be responding more consistently. Tonight it worked 100% of the time which it has never done before.

Thanks for the help.

BTW, I do have a small Oregon Scientific remote temp sensor that transmits the outside temperature to the base unit indoors. It operates at 418mhz and probably is the reason why I had significant interference at the MRF unit.

[Correction to this post.... The temp sensor actually operates at 433mhz, not 418mhz as incorrectly noted above... thanks to Bobli for catching this error]

The Oregon Scientific items I have transmit at 433mhz. Are you sure about the 418mhz?

I stand corrected... they are indeed operating at 433mhz. Must have had the wrong glasses on ;)

Does it make a difference if you use a ferrite core per each emitter wire vs wrapping 2 or even more emitter wires around a single ferrite core?

Electrically I don't think it matters. You introduce the same inductance into each wire regardless. You may have some physical constraints like fitting the connector plug through the ferrite core's doughnut hole along with multiple winds of the emmiter cable.

If you are using an MRF 300, 350, or MSC 400, I would think a Ferrite core on the Antenna Reciever would help. Anybody tired that?

Funny you brought this up now, I tried ferrite cores on the RFX at 3 seperate houses last week where we had RF issues with MRF-300s. In all 3 cases it solved the problem.

The core was 1" long, 1" diameter, and 1/2" hole through the middle. It was a split core so I could wrap the antenna wire through it 12 times. I do not know what type of ferrite it was, I've read "43" is the best material for around 400Mhz.

All 3 locations had severe enough RF that the RFX-150 LED would flicker and/or light fairly solid. After 12 wraps through the core, not a hint of interferance and the reception was exceptional.

Before I tried the ferrite I re-routed the wire and antenna to every possible location and unplugged the emitters but the light was still flickering.

The ferrite core had no effect at the MRF end, but placed within a few inches of the RFX it eliminated the interferance completely.

I used #43 and #61 cores and that fixed my problem.

The cores I have gave the following information:

#43 - Wide Band Freq(MHz)= 1-50, Attenuation RF Noise(MHz)= 20-600
#61 - Wide Band Freq(MHz)= 10-200, Attenuation RF Noise(MHz)= 200-1000

I used the #61 material on the emitters and the #43 material on the power line (MRF250).

Here is the company that manufactures the cores I used. This web page has some good information:

[Link: amidoncorp.com]

John

That's very interesting. I would have thought the ferrite would go near the MRF-350. Your experience would seem to indicate that the interference is coming from the wire INTO the RFX-250 and screwing things up before the info is sent into the MRF.
Thanks for this information.

Dave, this is actually what I expected because the RF circuitry is in the antenna. After the antenna receives the RF what is sent down the wire to the MRF is TTL type logic like an IR repeater system. Stopping the RFI before it hits the antenna through the wire seems to be a great solution. It seems the wire was pulling in too much stray RFI and sending it into the RFX and confusing the situation.

P.S. You referred to an RFX-250 above, just to clarify I have only tried this on RFX-150s I have never had RFI issues with an RFX-250 but I would guess the situation would be the same as the RFX-150.

This thread has been pretty quiet for a while. Any more feedback from someone who's used these techniques on some of their problematic installs?