JP1 Remotes

[banjo]

Is anyone having problems with limited range on the URC-9910 RF to IR blaster? I just got my unit from the X-10 super sale. However, the RF to IR part only seems to work if I am within about 25 feet of the blaster. Beyond that, it does not work.
I noticed an RED LED within the blaster that flashes intermittently even when I am not using the remote. Sometimes this LED blinks like a heartbeat about once a second. Other times it is OFF for a considerable amount of time. (It blinks rapidly whenever I press a button on the remote. )

Questions:
1. What kind of range are others experiencing? The manual says 100 feet. I am getting about 25 feet which includes going through a plasterboard wall.

2. Does the RED LED blink all the time in units that work? You have to look closely, because much of the light from the RED LED is absorbed by the IR window on the front. This LED is pretty much dead center in the unit.

3. Has anyone found a hack that will extend the useful range of these devices?

Thanks.

---- Steve

[banjo]

Just for clarification: The "blaster" is the 8-in-1 IR/RF Command Center. Part No. CCHAB01.

Thanks.

---- Steve

[The Robman]

The term "IR Blaster" doesn't refer to the command center, it refers to the little wire that you can plug into the command center where you would then tape the other end over the IR window of the device being controlled.

So your initial question sounded like you had a range issue from the RF base to the IR blaster. It's now evident that the range problem is from the remote itself to the RF base (ie, command center). This is a common problem and is caused by the environment where you are using the remote. There is obviously alot of RF "noise" in this location which is causing the base unit to fire off IR signals all the time.

There is indeed a hack to resolve this issue. Look at the sticky thread related to the 15-2117 in this forum, then look at the 8th post in it.
_________________
Rob
www.hifi-remote.com
Please don't PM me with remote questions, post them in the forums so all the experts can help!

[Tommy Tyler]

Steve,

Make sure you keep your thinking straight. There are two issues to this problem. First, there's the matter of sheer maximum range of the UHF radio signal from the remote to the Command Center. When the manufacturers say "up to 100 feet" they often mean if tested outdoors in an unobstructed field with nothing else around, an ideal environment that is free of interferring radiation from other radios or noise sources. The second issue is local interference. The receiver in this unit uses a superregerative detector (a design notorious for simplicity and sensitivity, but a little on the broadband side and lacking in ability to discriminate against unwanted frequencies) followed by a 3-stage amplifier and a level detector. The reason the base station often operates when you move closer to it is probably that the remote's signal becomes strong enough to drown out the interference.

The hack that has been published for alleviating the "busy red LED" problem is nothing more than a way to effectively increase the threshold of the level detector. That results in reduced sensitivity not only to noise, but also to the remote's signal. If that works I'm all for it, but I have a problem seeing it as a way to "increase the range of these things". I hope you have exhausted all the other possibilities (location of the unit, length of the antenna, experimentally turning off other nearby devices, etc.).

Incidentally, the base station says "FCC compliance" but doesn't give an FCC ID number. Does the remote itself mention an FCCID? I was unable to find this product listed in the FCC files for Universal Electronics, Inc.

Tommy

[mr_d_p_gumby]

[Tommy Tyler]

You may be right, Mike. Another possibility is that number right below the FCC logo on the base station that says "Canada: 1700 102 1610A". It may have been tested by the Canadians, and the files are there. I've been unable to find a web site for the Canadian equivalent of the FCC web site.

Tommy

[The Robman]

Hey Tommy, the id is DI2 9910, here's the link to the FCC info on the URC-9910.
_________________
Rob
www.hifi-remote.com
Please don't PM me with remote questions, post them in the forums so all the experts can help!

[banjo]

Ok, I took the base station apart. Unfortunately, R24 is already 220K ohms. (I guess the manufacturer also reads this forum! ) Not a whole lot I can do. I disconnected by cordless phone and several other items that could be radiating. But no improvement. Even with the unit disassembled and the antenna disconnected, I still see periodic LED activity. The three stage amplifier is using electrolytic capacitors for stage coupling. Perhaps one or more of these is a little leaky and is upsetting the bias. If I can get some low leakage tan. capacitors, I will try replacing them.

--- Steve

[Tommy Tyler]

Steve,

I've just posted a schematic of all except the UHF amplifier section of the 9910 base station in the File Section>Miscellaneous>Schematics folder, if it's of any help to you.

If you're getting random noise pulses with the antenna disconnected (case opened) you really have one sensitive unit there. Have you tried grounding the antenna connection tab?

For purposes of comparing notes, my understanding of the use of the 4093B Schmitt Trigger NAND is that they are using the typical 0.9V hysteresis as a peak-to-peak level detector. There's a lot of tolerance in the hysteresis, but assume it is exactly 0.9V and exactly centered between Vcc and ground. Then the positive threshold is 2.5 + (0.9/2) = 2.95V, and the negative threshold is 2.5 - (0.9/2) = 2.05V. With R23 and R24 equal, the average level of the AC coupled signal from C36 is centered at 2.5V, assuming a symmetrical output waveform from Q5. As long as the output of C36 is less than 0.9VPP, pin 11 remains high or low, wherever it was last left. When the output of C36 is greater than 0.9VPP, the positive and negative thresholds are both being triggered, so pin 11 switches high and low accordingly, causing IR transmission.

By changing R24 to 220K you drop the reference level of C36 average output from 2.5V to 2.0V, but the Schmitt trigger levels remain unchanged. So now the output of C36 must swing from 2.0V to 2.95V to trigger the upper threshold level. That's a positive swing of 0.95V, or a PP signal of (2 x 0.95) = 1.9VPP. So the change in R24 has increased the amplitude required to detect a transmission from 0.9VPP to 1.9VPP. If I'm correct, that means the remote's range has been cut in half.

Note that if the Schmitt hysteresis were perfectly symmetrical and centered between Vcc and ground, it wouldn't make any difference whether you changed R23 or R24 because all you're doing is moving the bias point off center of the hysteresis band so that a greater PP signal is required to cross both thresholds.

Obviously the purpose for C24 and R19 is to guarantee the LED's are all off during standby, regardless of whether pin 11 was left high or low by the last amplified signal. I haven't figured out the reason for D12.

The use of such large electrolytics for coupling amplifier stages is strange, considering that the signal being amplified is always at an infrared carrier frequency of 30KHz to 60KHz. Except for Q3, which has a low input impedance, I would have thought 1.0MFD couplers would be plenty. It's also sloppy design to use one "wide open" stage (Q3) followed by two more stages with gains of 10 and 4.5. All three stages could have been given a stabilized gain of 16 to 20 and accomplish the same thing.

Regarding your concern for leaky electrolytics, I don't see how that could do anything but REDUCE the sensitivity of the unit, by changing the bias of a stage so that it was "limiting" by clipping the positive or negative swing of the signal.

I've just guessed at the values of C16, C17, and C18. They should be to roll-off the bandwidth, starting around 60KHz, to filter noise. If I were going to try to de-sensitize a unit I think that's where I would start, rather than changing the output switching threshold, because if the noise pulses are narrower than the normal remote pulses you stand a chance of being able to filter them out without attenuating the useful signals.

Here's a couple of off-the-wall ideas. Most likely the noise signal is being picked up by the antenna and given the full treatment. But there's a remote chance the noise is getting in somewhere along the 3-stage amplifier. You can test that by grounding the base of Q3 to see if the LED stops blinking. If you want to experiment with grounding the entire circuit (which includes the shield box over the RF amplifier) it should be safe to tie it to earth ground because the transformer power supply is isolated.

Tommy

[mr_d_p_gumby]

[banjo]

Thank you very much Tommy for the schematic. I compared it to my unit and it seems to match very closely. I lifted C16-C18, C24, and C27 to measure them. The values I measured with a Fluke Multimeter were:
C16, C17 and C18 all 0.22nF
C24 = 47nF
C27 = 1nF

I removed the can from the RF section. It contains two transistors and several coils. The transistors seem to be configured as two common emitter stages. The first stage appears to be fairly broadband. The second stage has the tuning coil in its collector circuit as well as a large coil in its emitter circuit. The output from the RF section is fed through a 22K ohm resistor with a ceramic capacitor to ground before connecting to C10. This 22K seems to set the source impedance for Q3.

Here at work in a metal walled building the LED is quiet. At home, about 25 miles away, in a wood sided building, the LED chatters all the time. I guess I will try to hook a scope to the input of the bit slicer over the weekend to see if I can determine the frequency of the interference.
Other than simulating the circuit in SPICE to try and maximize the component values, my only other thought was to add some copper foil as a ground plane on the top of the board. The metal can shields the RF section on the bottom of the board. But the top of the board is unprotected. Since the board is single sided with no ground plane, the metal can is like an open bucket!

--- Steve

[SilentBob]

banjo

I just found your post from march.

Did you find a way to protect yourself from the interference or increase the range.

I don't know if you ever saw my post. I was looking into similar issues. I really wanted to increase transmit power, but I don't know enough about the electronics to do it properly. I achieved the same result by increasing the voltage of the entire unit. However, I would be interested to hear your thoughts.

Thanks.