Hi!
I work to an project and i need to use an remote control and an receiver. For this I bought an cheap remote control like this. Can be found searching on ebay for "key fob garage remote".
As receiver i bought an cheap model MX-RM-5V like this
I prefer to use this cheap receiver because is widely used in some tutorials and I'm a beginner.
Also i use RCSwitch as library to decode rf signals.
Everything works fine, but the receiver is very limited as range. So i try to find another receiver that can work with my remote but with better range. I don't need some unrealistic range (hundreds of meters) but something with stable range between 15-20 m (open field) will be good enough.
Searching over internet i found some receivers (superheterodyne with RXB5 or RXB6 chip) witch seem to be better than cheap MX-RM-5V but i'm not sure if is supported by RCSwitch or is compatible with my remote.
Everyone who can give me some advice big thanks!
The antenna is extremely important. You will get the best range with a balanced dipole, shown below. One end of the dipole (at center) is connect to the ANT terminal of the transmitter or receiver, the other to GND.
I get 300 meters line of sight range with the setup shown below.
In the UK you're allowed to radiate -6dBm in this band.
I've obtained a 50m range with -6dBm Tx power , and a simple superregen receiver, sensitivity -97dBm
in open air using loaded 1/4 wave whip antennas about 8cm long. The data rate was 1200 baud, and used ( obviously) simple on/off modulation
A dipole would give about 1.6dB more - not very much.
Obviously if there are obstacles or bad reflections this would make things worse.
If you're allowed more power where you live you'd get better range. And a better receiver would improve things too.
I've obtained a 50m range with -6dBm Tx power , and a simple superregen receiver, sensitivity -97dBm in open air using loaded 1/4 wave whip antennas about 8cm long.
As noted above, I get better than 300 meters line of site with two balanced dipoles and a superregenerative receiver. The same setup with just 1/4 wave whips gives 50 or so meters.
Radiation efficiency calculations for the 1/4 wave whip assume an effective ground plane, and in the real world (i.e. the hobby bench or a model), there is seldom a reasonable or effective ground plane adjacent and perpendicular to the antenna.
Poor ground plane performance is often the cause of low range or outright failure of hobby radio projects.
I usually use the easy to construct "sleeve aerial"
Use a length of thin coax with braided shield, and connect one end to receiver hot and ground.
Strip about 25cm of the outer plastic from the other end, and pull the braided shield back over the plastic of the coax.
Cut both center core (leave the plastic on) and shielding to the right equal length for the frequency of interest.
Put some heatshrink over the whole length of shielding and center core, and hang the aerial vertical from the tip. You now have a vertical (less dead spots) 1/2 wave dipole with inbuild balun.
Leo..
Cut both center core (leave the plastic on) and shielding to the right equal length for the frequency of interest
Yes, this works very well too, but I find it to be a bit harder to make than a balanced dipole.
Just to be clear, for proper operation it is important that the shielding be widened, turned inside out and then pulled back over the unmodified portion of the coaxial cable (cover that portion completely with the inverted shielding). The outer surface of the exposed, inside out shielding becomes one of the radiating elements and should be slightly less than 1/4 wavelength in length.
Yes, therefore you start with 25cm, and end with about 18-20cm of braid over the outer part of the coax.
Cut braid length to ~0.95 * 1/4wavelength, and the isolated centercore also to ~0.95 * 1/4wavelength.
A length of >=1/2wave of heatshrink keeps it all in place.
The piece of coax with braid over it (the sleeve) is a 1:1 balanced to unbalanced balun.
You should in theory use a balun with a halfwave dipole.
Leo..
@Allan.
I usually try to cut the length of cable at whole wave length times the velocity factor of the cable (e.g. 0.66), to limit possible mismatch/standing waves. Easy to do that with a dipole or 1/4wave, but not sure where to start measuring with a sleeve aerial. At the middle of the dipole, or at the end of the braid.
I guess at the end of the braid, because the braid is part of the balun.
Maybe you can answer this.
Leo..
obviously the sleeve has to be cut to that length, but for the free part 0.95 is a good enough guess.
The length of the feed to the braid split doesn't matter - it's a transmission line. Measure from the end to the split point - and make the braid cut length fairly short - < 3mm would be fine at these frequencies.
Dipoles aren't that fussy.
regards
Allan
ps download a free copy of RFsim99 - written by an old colleague of mine. It's not HFSS, but handy for simple RF work...
Knew all of this, because I read "Karl Rothamel's Antennenbuch" many moons ago back to front multiple times.
Thanks for the reply anyway, but I think you missed the real question.
You can minimise problems of receiver impedance, cable impedance and aerial impedance by using the right length transmission line. Reflections are in the same phase with single or multiple wavelength * Velocity cables.
I found that cheap superregenerative receivers without frontend easily "detune" and get very insensitive with the wrong aerial. Maybe I'm nitpicking here.
Leo..
It is well worth considering the Si4432 based FSK tranceivers. These can be bought for about £1.50 each. They are packetised data devices.
On of the issues with the simple UHF trancievers is that a lot of them are on a few limited frequencies. So interferance from other devices can be an issue. With the Si4432 you can choose the frequency of operation and thus avoid local interferance.
An Si4432 will put out as much as 100mW, but you can scale it back to comply with local regulations, 10mW in a lot of places, including the UK.
You will have a comms link that has far more range than you may ever need, a 10mW Si4432 setup will do around 12kM LOS on simple 1/4 wires, but the advantage in your case of this type of capability it that for short range use you dont need to worry too much about antennas.
A transmission line is length independant only if correctly matched . The antenna at it's tuned freqency should be OK - but the input impedance of a super-regen probably isn't. I think they're awful - apart from their easy detuning , poor sensitivity and terrible blocking performance they radiate at somewhere near their nominal receive frequency and upset other receivers in the area. A gain stage in front improves things, but I'd still pay a bit extra for a better architecture...
You can't even measure their input impedance with a VNA, because the emitted signal interferes with the VNA sampling signal! And even a gain stage's S12 isn't zero, so you're still confused.
Without knowing the input impedance you can't determine the correct length of transmission line except by using a trombone and an on-air sensitivity measurement - preferably in an anechoic chamber. It's been done. You're using the poor VSWR as a matching component.
horrible things . I designed a couple once under protest because the client was too mean to pay for a better design..
Today i make some test with different antenna length.
without any antenna wire i have about 2m range
with 17cm antenna straight - aprox. 4m
with dipol how suggest @jremington i don't see any relevant improvement
with 34cm antenna - aprox. 8m
with 51cm - no improvement
Again i use am remote like i say in first post, not pair transmitter-receiver
So i think that this type of receiver It is not good enough. I honestly do not understand how I can get some users distances of tens of meters.
Still not have any suggestion about receivers that I mentioned in first post.
@srnet
I see many wireless transmitters but big question is: my actual remote will work with this receiver? I see that support OOK modulation mode. I'm not expert but i think that all these remotes like mine support ASK modulation.
Receivers that i mentioned in first post support ASK modulation so most probably will work with my remote.
Superheterodyne receiver have better range that super regenerative?
Sorry vlad2005 - missed your questions in the first post.
As to your variants.
they're all OK
#1 Probably OK, but doesn't specify bandwidth or modulation method.. unhelpful, and though the quoted sensitivity is -116dBm, without this info it's hard to guess what that means. I approve of the shielding can, though. The transmitter's 25mW is about +14dBm - a lot
but #2 OK as well if you buy tx/rx pairs they should work well together. +11dBm tx power is plenty - you should get reasonable range - at least 50m in free air.. And -110 sensitivity for it's bandwidth is reasonable. It implies a noise figure in the region of 12dB, which isn't brilliant but usable.
Neither generate or interpret the codes - you'll have to do that with an arduino, for example.
#3 is much the same as #2 .
The helical antennas described in #2's advert should be fine, with a gain a little less than a 1/4 wave, but much more compact.
You could make one and try it with your existing receiver .