I’m new to this product, but very interested in building a permanent agricultural setup with multiple reach RS+ units.
Firstly, I want to build a fixed base station on my farm, with the Reach on a concreted tripod, and connected to a 915MHz antenna which is several meters away and elevated on a permanent tower. Can the Reach MCX antenna port be extended by a cable and attached to a product such as this, without any adverse effects?:
Secondly, because the Reach units will be permanently fixed to tripods and tractors and exposed to the elements, I want to avoid using the side USB port and only use protected connectors on the underside of the Reach. Is there a panel underneath the Reach that can be removed to directly plug in a solar panel etc or 12V DC? Or can I purchase the DB9 extension cable and splice DC power into that?
Ideally, on the rovers, I would like to have just the DB9 extension cable coming out of the Reach, and plugging into my tablet which controls my autosteer systems. Is it possible to somehow supply both power and data transfer through this RS232 link (maybe by modifying the cable?)
Yes, you can connect an external antenna to Reach using an adaptor. Please take into consideration, that it’s feasible only for Reach M+, cause Reach RS+ has its own built-in antenna. Is there any specific reason why you don’t want to use Reach RS+ as base station?
You are right, you can supply power to Reach RS+ directly through the external port using this cable.
Yes, it’s possible. You can find the bottom connector pinout here.
Sorry, I probably should have said aerial instead of antenna. Wondering if I can extend the LoRa radio aerial by a long cable (about 15 metres) with a male SMA plug to an omidirectional aerial like the one linked above. Reasons being, I need elevation for LoRa line of site to all farms for RTK, I want to keep the Reach RS close to the ground to ensure no horizontal movement, and I’ve also been told that the NMEA string only allows for about a 6 meter height offset from a ground point for the Reach GPS antenna? Meaning I can’t accurately have the Reach RS on a shed rooftop? Not sure about that last point though.
And thanks heaps for those diagrams. I must have missed them. That will work a treat.
I’d say the signal loss will be huge, especially if its a very small RG-type coax cable. The losses on those cables will probably outdo any signal advantage in having a directional or omni antenna with high enough gain.
Your best bet is to keep the antenna cabling as short as practical, use a larger gauge/thicker coax cable with lower loss.
Otherwise what’s usually done in survey and Ag is to place a higher power radio at the base or run the radio output via an amplifier (JD do this in the states with their UHF base setups on GreenStar).
I’m not sure the practicality, cost effectiveness or legality of doing that with low-power LoRA signals though.
Yeah thanks for that info! I’ve been wondering that myself lately. So you do lose some signal through the cables, do you? I do need the height with my setup. I have some pretty serious earth embankments that I need to get over. So I’m looking at 20m of cable. I’ve been looking into the possibility of building my own coax cable with a really high gauge. But I hadn’t thought about an amplifier… that could be the answer. +30dbi at 5V looks very cost effective. Will that sort of power be enough to get through 20m of cable to a 12dbi omnidirectional antenna? Combined with the 20dbi tx output of the reach? Legality shouldn’t be an issue with my current licensing, but it’s definitely worth me double checking.
With a 20 meter pole, pitching and rolling of the vehicle will pose a serious precision issue.
It will deviate to an extent where you could put a phone gps up instead and get the same “accuracy”…
At 10 degrees you are looking into an offset ~3.5 meters. At 20 degree ~7 meters.
Thanks for your info and calcs, but this is a different application. Base station, not rover. And the 20m pole is just for the LoRa extension aerial connected to the base unit. The Reach will be on a concrete pole, about 1m high.
Yeah sure! Thats good to know. I’ll definitely look into the amplifier options then. Do you think an extra 30dbi at 5V would cut it? Or do you recommend any amplifiers? I’m really just after a solid 5-10km baseline.
I think the first thing is to look into a proper antenna, and then concentrate on the amplifier. With your setup, it it crucuial that you are amplifying the signal, and not the noise, so you need a good antenna.
I’d start with a low loss coaxial cable, something like an LBC400 we get here in the UK will give you a loss of 12.8 dB per 100m, so 20 metres gives you an approximate cable insertion loss of 2.6 dB. That cable has a jacket diameter of around 10mm. I’d use that as a yardstick to source an equivalent coax in your location, possibly look for something like RG213…
Smaller gauge 50-ohm coax RF transmission cables may be cheaper or slightly easier to handle but their insertion losses will be much greater, negating whatever gains you make with a high gain antenna mounted up high.
Now I’m assuming you will want an omni-directional antenna, so ideally something with 6dbi or more of gain to offset the inherent cable loss. The last antenna I bought here for one of my UHF masts I had matched to my base frequency for best results. No doubt you should be able to find an equivalent specialist radio antenna supplier in your locale.
They’re about £90 over here, but the gain is impressive at 12 dBi
So even with a cable loss as per previous post of about 2dB (if you’re careful with your cable selection and lengths), you are still looking at a net gain of 10 dB which is not to be sniffed at.
Thanks heaps for that! Really helpful. Australia sells a variant of the LBC400 that looks very similar. I’ve attached the link:
It advertises “0.151dB/m @ 940MHz” loss which would lose me about 3dB. I’ll definitely steer clear of the cheap RG coaxials.
So correct me if I’m wrong, but even 3dB of loss doesn’t seem that bad to me? If the reach is pumping out 20dB/dBi, I’m still getting 17dB without an amplifier setup yeah? And then, showing my inexperience of antenna solutions here, but are you saying that the dB of an antenna actually ADDS dB to the total equation? So if I had a 12dBi antenna, would that mean, accounting for cable loss, I would have a total gain of 29dBi? Which is still 9dBi over Reach RS stock! Is that right? I think that would give me a stable baseline of 8-10km at least?
I’ve found the omnidirectional Taoglas products a little find to hard in Aus, but there are a few dealers I’m yet to call. I’ve also got my eye on this one, though 12dBi is impressive.
So 20 dBm output power works out as about 0.1w of radio power. The decibel scale is logarithmic rather than linear, so that -3 dB of introduced cable loss means you lose half the radiated power of the radio just travelling down the end of the coax. Effectively your output power is 0.05w of radio power before you get to your antenna.
The antenna however has gain, so it takes the 0.05w of radio power and in the case of a 12 dBi gain omni-directional antenna radiates out the equivalent of 29dBm or almost 0.8w of power.
So very simplistically (we are ignoring the effects of noise) your effective isotropic radiated power (dBi) would be 8 times the output power at the SMA jack with a 12dBi gain antenna and 20-ish metres of LCU400 coax connecting it.
[…and I believe you are still legal]
Not sure what the RF/radio scene is like back in oz, its been a long while since I lived there. But it should be possible for an antenna maker to make up, for reasonable outlay, a fibreglass co-linear antenna to match up to the 915 MHz ISM frequency for LoRA you guys use.
Ahhh log scale. Everything makes a lot more sense now. Okay. So, just so I make sure my math is on the same page, log laws dictate you can just add logs together, thus correctly multiplying the log products. So, log(A) + log(B) = log(A*B). So in theory, if I have 20 dBm output out of the reach rs+, 25m of LCU400 with a loss of 0.151dB/m, and a 6.2dBi gain antenna, I can sum those logs to equal a total of 22.425dBm effective antenna output? So then if I strip away the logs and convert to watts (P(W) = 1W ⋅ 10^(P(dBm) / 10) / 1000), I would would get 0.175W of effective antenna output power? Am I thinking about it the right way now?
In Oz we’re allowed a maximum of 30dBm or 1W for the 915MHz spectrum, which is what I’ll be using. But I’m going to double check that…
Again, thanks heaps for the help mate. That vid looks great. Looking forward to buying the parts and putting the system through it’s paces. I’m thinking I will not bother with an amplifier at this stage, and just give it a go without one, priotising high quality cable and antenna instead. I can always add one on. But I will post the results/achieved baseline in this thread.
Just to step sideways for a moment. Your requirement is to have a GNSS receiver near ground level, and also a telemetry broadcast antenna at 20 meters elevation.
OK, so what makes the most sense to me is to put the radio up the pole. That way, you are running regular communication cable for 20 meters+ with power and can have a very short RF cable for max dB.
