Maximizing range of cheap remote triggers - Page 1
Forum section: electronics / rf-microwave

author: Peabody
author_rank: Super Contributor
timestamp: August 23, 2019, 09:56:42 pm
content: I've picked this type of device to remotely trigger my Canon DSLR:https://www.ebay.com/itm/IC-2262-2272-4-CH-Key-Wireless-Remote-Control-315MHZ-Receiver-module-F-Arduino/311572565319That setup is shown in the third picture below. And it works fine, except for the range. Now I know there's a limit to what you can expect from a $3 device, but I just wondered if anyone had any suggestions concerning the antennas. I should say up front that I'm a hobbyist, with no training or experience in RF at all.I have not been able to find schematics that match these circuits. The chips are the PT2262 transmitter and PT2272 receiver. The datasheets aren't helpful, at least not to me.The first picture shows the transmitter, with the back flipped horizontally so both sides appear oriented the same. The part labeled Y1 is marked R315, so I assume that's how they get 315 MHz. If I add the length of the large traces on the board to the length of the extended whip antenna, I get about 8.5 inches, which I think is a little short of the 8.9 inch 1/4 wavelength. Also, I'm not sure the trace portions that lie directly behind the whip antenna should count toward antenna length. So I wonder if adding additional length to the whip would improve range.The second picture shows the receiver. It doesn't have an antenna, but has a hole for soldering one in. The question is how long it should be, and what shape if that matters. Also, there is exactly one adjustable part, and that's a slug of some type, but it's not obvious what the appropriate test point would be for adjusting that slug.At this point, all I would know to try is soldering a too-long antenna, say 11 inches, to the receiver, get someone to work with me to determine the range that produces, then start cutting the antenna shorter, which theorectically would increase range, and keep doing that until cutting starts to decrease range. But it would be a lot better if there was some place on the receiver board that I could just measure a voltage level and use the same cutting process to find the maximum voltage there when the transmitter is firing. However, that doesn't really help with the frequency match (presumably the slug) or the transmitter antenna question.Other questions:All the docs for the receiver say the power is 5V, but both the PT2272 and the LM358 can go much higher. If I use a 9V battery, is that likely to degrade performance or improve it? Even if the chips can take 9V, does all the RF stuff and tuning go to hell with the higher voltage (dividers, or whatever), or does the S/N actually improve?Would making the antennas 1/2 wavelength materially change things?Well, I would appreciate any ideas for how to approach this issue. I was thinking if I can get a reliable, easy way to maximize range, I might make a video. I mean, if you could actually get a 100-meter digital trigger from a $3 setup, that would be pretty cool.

author: tautech
author_rank: Super Contributor
timestamp: August 24, 2019, 12:24:30 pm
content: Most of these receivers I’ve bought had a coiled antenna wire like wound around a pencil.50-75mm long wound with probably 300-400mm of single strand insulated wire.Easily gives 100m range using those 4 button remotes and with a properly built and tuned antenna 500m reliably.The 2 channel system in this listing shows a coiled antenna behind the relay board:https://www.ebay.com/itm/1-2-4-6-8-12-15-Channel-DC-12V-Wireless-RF-Remote-Control-Transmitter-Receiver/312249920490?hash=item48b38babea:m:mhiFxrT9f7rUQo8yOc0jljgI got mine directly from these guys (scroll down)https://www.rfremotech.com/FiringSystems.htmlTheir long range transmitter units could do 10km !Testing tips.Use the receiver to switch a halogen or LED lamp pointed to where you can see it and then just keep adding distance between the transmitter and receiver.Depending on the receiver type as to whether you have a momentary or latching/toggling unit. The toggling unit needs another channel activated to turn the active one OFF.

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 24, 2019, 01:10:05 pm
content: I remember hacking a similar remote for more range by reconnecting the transmitter supply to the full battery voltage, bypassing the regulator.

author: Peabody
author_rank: Super Contributor
timestamp: August 26, 2019, 05:29:39 am
content: It turns out Ebay has 315 MHz helical antennas. Maybe one of those would be optimal for the receiver. They look to be 27mm long, and consist of about 35 turns. That would be 22 gauge, maybe 24. But I don't know if this is better than just a length of straight wire.

author: james_s
author_rank: Super Contributor
timestamp: August 26, 2019, 05:39:29 am
content: If a directional antenna would work for your application you might try that, you can get a significant amount of gain that way.

author: tautech
author_rank: Super Contributor
timestamp: August 26, 2019, 05:47:21 am
content: Quote from: Peabody on August 26, 2019, 05:29:39 amPretty much anything should give you the 100M you're looking for as I was getting 500 (unreliably) with a 250mm length of stainless wire stuck into a BNC with a foot of coax soldered into the receiver PCB.There was some variation in these cheap receivers and I only ever bought the superhet models in so all my comments are based on these experiences.

author: David Hess
author_rank: Super Contributor
timestamp: August 26, 2019, 03:32:51 pm
content: I have done this sort of things before. I found that significant improvement with minimum effort could be had by using a basic dipole or loop antenna structure with a single adjustable element tuner like an LC matching section and adjusting for maximum signal strength on a signal strength meter.Trimming antenna length can work also but takes more time to get right. Of course anything is likely to work better than the tiny stock antennas.

author: Peabody
author_rank: Super Contributor
timestamp: August 26, 2019, 05:15:47 pm
content: Quote from: David Hess on August 26, 2019, 03:32:51 pmAs I said in the first post, I have no experience with RF, and don't even know what a signal strength meter looks like. However, the attached schematic appears to be pretty close to the hardware I have. If you were going to measure signal strength voltage, where would you do it?

author: David Hess
author_rank: Super Contributor
timestamp: August 26, 2019, 05:51:23 pm
content: Quote from: Peabody on August 26, 2019, 05:15:47 pmThat is sure a problem. When I did it, I used aHeathkittunnel dip meterwhich could also operate as a wavemeter which is a passive tuned receiver.Another way which sometimes works if you lack a signal strength meter is to measure the transmitter's supply current and tune for maximum current draw.If the receiver you already have has some way to report back signal strength, that would be ideal. But you might be left with only a works and does not work indication which makes things difficult.

author: Peabody
author_rank: Super Contributor
timestamp: August 26, 2019, 08:21:49 pm
content: I was thinking maybe trying to measure voltage at pin 5 of the LM358 which is where the signal first feeds into the opamp. I think this is basically on/off amplitude modulation, so I assume the LM358 is what converts the RF into some kind of demodulated digital signal. Anyway, I'll see if I can find some useful measurement on one of the opamp pins.

author: tautech
author_rank: Super Contributor
timestamp: August 26, 2019, 08:46:58 pm
content: You're overthinking this.Add some/any antenna to it, place it in a position where it can switch a light and start backing away from it turning the light ON and OFF until you see it failing to register the remote key presses.Modify the antenna if required and rinse and repeat.