JP1 Remotes

[SilentBob]

I got in on the X10 HTPro deal. I'm replacing an older 9910 with the donut ring.

What is interesting/bothersome, though, is that the 9910 seems to have a bit more transmit power than the HTPro. In my basement room I have a very hard time getting the HTPro to work, but the 9910 works acceptably.

I popped the remotes open and I noticed that there is some sort of variable component on the RF puck. Can that be adjusted in any way to to get better performance?

Is there any other upgrade/modification that could be done to increase the transmit power? The 9910 is "acceptable" but I would be even happier if the transmit power was even higher.

Thanks.

[Tommy Tyler]

SilentBob,

The adjustable device on the puck is a variable capacitor that was tweaked at the factory to set the transmitter output at 430Mhz. Whenever you see a difference in performance it's natural to wonder if that adjustment is slightly off. Maybe it was assembled on a Monday when the technician had a hangover, and all that. I know that's what I always think about. One of my lifelong ambitions is to find a simple, low cost way for guys like you and me to measure that frequency.

Experimenting with this adjustment is not for the faint of heart, but if you're the courageous sort, here's some info that will help. First, some details about the capacitor itself. If you look down inside the center hole you'll see the rotary part. It has a screwdriver slot with one end of the slot shaped like an arrowhead so you can keep track of the position. The rotor rotates continuously. Looking at the "D" shape of the device, call the flat side "south" and the round side "north". The value is minimum when the arrow points south and maximum when north. When the arrow points east or west the value is half way between minimum and maximum.

Turning the rotor from south to north increases the capicitance from about 1 to 2pF. So from the average value of 1.5pF when pointing east or west, you can change it by plus or minus 0.5pF, or 33 percent, by rotating it plus or minus 90 degrees. That's like a 2 percent change for every minute on a clock face. With a steady hand one can probably adjust this device within 1 or 2 percent. The problem is, how to tell when the output frequency is correct without an expensive RF frequency counter.

It can be done experimentally, using your receiver by trial and error to determine if the range improves or degrades after making a small adjustment, a tedious and time consuming process. You need a 3/32" or 1/16" flat blade screwdriver and a strong magnifying glass, preferably a jeweler's eye loupe. Before making any adjustment, scratch a tiny mark into the plastic case showing the initial position of the arrow. If the mark is slightly off, make a sketch showing its location relative to the arrow in enough detail that you could try to restore the original position if necessary.

First, find the maximum approximate range of the remote by backing off until operation begins to falter. This is not a precise procedure. Then carefully make a very small adjustment to the capacitor in either direction. For reference, the width of the screwdriver slot at the end corresponds to about 22 degrees of rotation, or a change of about 8 percent in capacitance. I suggest trying about half that. That is, turn the rotor until the center of the slot at one end moves over to where the side of the slot was. Recheck the range to determine subjectively whether it is improved. If the distance is less, try a small adjustment in the opposite direction. If it is better, try a little further in the same direction. Depending on when your patience (or you legs) wear out, you may be able to tune for maximum range this way. Don't leave the screwdriver in the capacitor while making a test. The metal can affect the capacitance value.

The semi-circular loop of heavy wire on the puck is the transmitting antenna. It is also an inductor in parallel with the capacitor, and what you're adjusting is the parallel resonant frequency of this inductor-capacitor pair. Make sure the inductors look more or less the same on both pucks. Any change in the shape or location of the antenna (such as bending it away from the board slightly) can affect its inductance, and consequently the resonant frequency. I thought I remembered that the screw holding the board down was plastic, because it's right in the center of the antenna loop, and can also change the inductance if it's any kind of metal.

I have to tell you, I've never tried this before, partly because I don't own one of these units. You may be discouraged by the tediousness of this, and opt not to spend the time. But if you do charge ahead and try it, please let us know what happens. You'll be a hero, the first one to try it.

Tommy

[mr_d_p_gumby]

[zaphod7501]

A fiberglass or hard plastic screwdriver would minimize the effect a metal screwdriver has on the control, although downward pressure also effects the control setting.

A digital camera or camcorder would let you "see" the IR output but you would probably need to close the IRIS down a bit or the output would swamp the CCD imager in the camera and hide differences. If you don't have IRIS control then "High Speed Shutter" or "Sports" mode could give the same effect.
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Just call me Zaphod (or Steve) --- I never should have started using numbers in a screen name but I just can't stop now.

[Tommy Tyler]

That's an excellent idea, Mike. This works if you just plug a miniature piezo beeper into the external emitter jack of the base station. I had no problem getting at least four different models from my junk collection to work. The sound level varies with the particular model beeper. Make sure you use one that will beep if powered by a single battery cell. You will immediately notice the random clicks corresponding to RF noise pulses, and when the remote signal is picked up it sounds like a rattle snake. There's no problem at all in distinguishing whether the remote is being received, versus noise. In a quiet environment I think you might be able to hear it 100 feet away. If it's not loud enough, run a long cable to bring the beeper back closer to your transmitter point.

I like this idea so much I'm going to suggest that everyone install a small beeper in his base station. The slight noise when you're actually transmitting is not bothersome, but at other times it sounds like a Geiger counter, and the intensity of the clicks warns you of the presense of noise.

Tommy

[Tommy Tyler]

Stop the presses! It doesn't have to be a piezo beeper. ANY loudspeaker will do. I tested everything from tiny 8 ohm, 1 inch diameter speakers to 100 ohm, 3 inch diameter ones, and they all give more sound volume than a piezo. And if you want to hear it a couple of hundred feet away, use a nice little speaker enclosure, perhaps an old shelf speaker you're not using. Just connect the speaker to a miniature phone jack and plug it into your base station.

Tommy

[zaphod7501]

You beat me to that suggestion but I was going to either add a resistor or an LED in series with the speaker to reduce the load on the circuit. 100 ohms is still pretty close to a short and would probably disable the LED it's connected accross.
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Just call me Zaphod (or Steve) --- I never should have started using numbers in a screen name but I just can't stop now.

[Tommy Tyler]

Sorry, Steve, think again.
The LED has 1.5 volts across it. A 100 ohm speaker at that voltage will draw only 15mA, leaving 225mA for the LED. Now an 8 ohm speaker will try to grab 190mA. But your point is well taken. IF one wanted to permanently install a speaker, and IF one didn't want to diminish the light output of ANY of the internal LEDs, then the best speaker choice would be one with high impedance, perhaps a 100 ohm or 45 ohm intercom speaker. But for temporarily plugging in a speaker for testing, or if the light output of just one of the internal LEDs can be sacrificed, then any impedance is OK.

Incidentally, a speaker can likewise be plugged into a cone or pyramid receiver of the RCA/Panasonic/Powermid type, but in that case the situation is reversed. That jack is in series with the internal LEDs, so you need to use an 8 ohm speaker, which will look about like an external emitter with 240mA passing through it (8 ohms x 0.24A = 1.9V). I added complete info on all this to my soon-to-be-posted article on how these range extenders work with external emitters. The article suggests using a speaker-equipped receiver as an audible RF noise sniffer. By moving it around a room you can search for sources of persistent noise, or search for a noise-free location for the receiver. It's also handy for testing to see if your remote is being received reliably in another room.

Tommy

[Tommy Tyler]

For the benefit of all who have been following this thread, I've just posted an article in the Files>Miscellaneous>Hardware folder entitled "Remote Control Range Extenders" that should provide all the information you need for adding all the external emitters you want to UHF receivers, such as RCA/Panasonic/Powermid cones and the 9910 Command Center base station.

Tommy

[SilentBob]

Tommy,
Thanks for the info.
If I can get my hands on an oscilloscope, I should be able to use that to fine tune the antenna to 430Mhz, right?

If so, I think my boss has one I can use. Otherwise, I'll try the manual tuning method this weekend.

Now, realizing that adjusting that capacitor will only tune the transmit frequency, I was wondering, would there be any way to build a simple amplification circuit that would actually boost the RF output?

I wonder if running the remote off a 9V battery would upset the rest of the electronics....

[Tommy Tyler]

SilentBob,

>> ... I should be able to ... fine tune the antenna to 430MHz, right? <<

The problem with using a 'scope (not counting the fact that a relatively rare 'scope with about 3GHz bandwidth is required) is that you can't connect it directly to the transmitter without loading down the circuit and changing the frequency. To tune with a 'scope you would need to either pick the signal out of the air with an RF probe, or tap off the RF signal at the output of the base station RF amplifier, before it gets demodulated. Then you could tune the transmitter to 430MHz and, after that, tune the receiver for maximum signal amplitude at that frequency. Remember, the transmitter has a single frequency, whereas the receiver has a bandwidth, or a small range of frequencies that it is sensitive to. If you tune the receiver it means you set the middle of that range to 430MHz. When they manufacture the base station they do that by transmitting from a crystal-controlled 430MHz source and tuning for max reception.

All the foregoing is an order of magnitude more difficult than empirically adjusting a transmitter for best reception, and is certainly beyond my abilities and resources.

>> ... any way to build a simple amplification circuit that would actually boost the RF output? <<

I don't know how to do this, but I do know there's no such thing as a "simple" 430MHz amplifier.

>> running the remote off a 9V battery would upset the rest of the electronics... <<

You bet it would.

[jherrick]

Bob,
One thing that what unclear to me from the beginning post was this: Is it your IR or RF signal strength that seems weaker? Tommy has run with the idea that it was the RF that you were referring to, and probably correctly so. It has also spurred some interesting discussion.

I just wanted to point out, however, that if it was IR signal strength you were referring to than all of the discussion above is for naught, as the puck has absolutely nothing to do with the IR strength.

Just want to clarify for anyone just coming into this thread that has the same confusion I do. Is it IR or RF that is suffering?
Jim

[Tommy Tyler]

Good point, Jim. And to add to the confusion, there's the IR signal strength from the base station and the IR signal strength from the remote itself.

Tommy

[MaskedMan]

Silentbob was referring to RF, see his posts in this thread: http://www.hifi-remote.com/forums/viewtopic.php?t=284
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Edmund

[jherrick]