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Transmisson power TX Modules
#1
Question 
Hello community,

first I wish everybody a nice Sunday  Smile .

Disclaimer: Be aware of regulations of your country in sight of transmission power since the EIRP is relevant and you can have some additional gain because of beam effects of your antenna.

Since I have to bridge a pretty far distance with my TX modules with parts of houses and vegetation in between I had a poor transmission efficiency in my first tests.
I tested with different types of antennas in different angles and so on...

Moreover I saw, that someone here added a RF amplifier to get more transmission power.

I tried to find a datasheet of the transmitters used on the TX board and I found the following:
http://www.tpelectronic.ir/datasheets/20...005328.pdf

The input voltage vs. transmission power curve says, that it rises with about 0.85 dbm per additionally applied supply volt. This means you can gain 2.6dbm when suppling the transmitter with 12V instead of 9V. The negative aspect is, it will have more stress and may die earlier - which is in sight of price and simplicity of changing acceptable.

After reviewing the TX schematics, the 9V rail, after the 7809 linear regulator supplies:
 - Transmitter
 - Fan
 - Fan LED
 - 1117-5 linear regulator of 5V rail

So in my opinion it should be no problem to supply the TX board with 12V DC by changing the 7809 with a 7812 linear regulator or sourcing it directly with a 12V stabilized power supply by bridging the 7809. When supplying it with a battery you would have to integrate a Buck-Boost-Converter and prevent the battery from deep discharging.

So what's your opinion oder did I miss some trace in the schematics.

Best regards, engolling
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#2
Hi,


I once did some experiments, and I found out that the increase in voltage for the transmitter from 9 to 12V did not increase the intensity
of the electromagnetic field signal at the reception site ...  Sad

I think it is better to take the path of proper antenna selection and their proper routing in conjunction with the choice of good location for RF device.
Best Regards
Zdenek

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#3
(14-10-2018, 19:08)hornychz Wrote: Hi,


I once did some experiments, and I found out that the increase in voltage for the transmitter from 9 to 12V did not increase the intensity
of the electromagnetic field signal at the reception site ...  Sad

I think it is better to take the path of proper antenna selection and their proper routing in conjunction with the choice of good location for RF device.

Hello Zdenek,

thank you for your feedback and sharing your results. I'm just wondering, because the datasheet says otherwise.

Maybe I have to search somebody who can measure the output power to be sure what is happening.

Regards,
engolling
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#4
(14-10-2018, 19:51)engolling Wrote: thank you for your feedback and sharing your results. I'm just wondering, because the datasheet says otherwise.
Maybe I have to search somebody who can measure the output power to be sure what is happening.

Hi again,
I used a RTL SDR scanner for it - it is super! https://learn.adafruit.com/freq-show-ras...dr-scanner



Bye.
Best Regards
Zdenek

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#5
Hi engolling

From my experience with those modules, increasing voltage above 9V brings more problems than solutions, specially frequency shifting. Also they don't last so much when powered by 12V.

When I saw the metal box you have designed for housing the two TX units one thing has bring to my mind: he will have to use an coaxial extension between the SMA connector on the TX board connector and the antenna. Be careful with this approach, attaching the antenna directly to SMA connector on the TX board is always the best.

If you would like to experiment with a different transmitter module, try this one:

H34C 433Mhz ASK MINI RF Wireless Transmitter Module  

The pinout isn't compatible with the TX board, but it isn't difficult to adapt. I'm experimenting these small modules since months, and found they are more stable in terms of frequency shifting.
MeteoCercal - Air Quality Data
Click here to watch at my ThingSpeak channel



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#6
(14-10-2018, 23:00)Werk_AG Wrote: Hi engolling

From my experience with those modules, increasing voltage above 9V brings more problems than solutions, specially frequency shifting. Also they don't last so much when powered by 12V.

When I saw the metal box you have designed for housing the two TX units one thing has bring to my mind: he will have to use an coaxial extension between the SMA connector on the TX board connector and the antenna. Be careful with this approach, attaching the antenna directly to SMA connector on the TX board is always the best.

If you would like to experiment with a different transmitter module, try this one:

H34C 433Mhz ASK MINI RF Wireless Transmitter Module  

The pinout isn't compatible with the TX board, but it isn't difficult to adapt. I'm experimenting these small modules since months, and found they are more stable in terms of frequency shifting.

Hello Werk,

thank you for your feedback. 
That was the main reason why I was asking, if someone has experience in supplying the transmitter with more power.

Concerning the box and the antenna - i don't see those problems in using a coaxial cable as extension. In using a good quality wire the attenuation should me very small. Im my opinion it is much better to use a longer coax wire to bring the antenna in a better position, because signal loss in the wire is ways less then in the air. In addition the wave impedance of TX Module, Wire and Antenna have to be matched.

The H34C module also does not have more transmission power, but as you say, the frequency maybe more stable.

What do you think about this transmitter:
https://www.aliexpress.com/item/433MHz-5...8e5bb6f171

Should have a lot of power and might also be compatible because it is using amplitude shift keying.

I have some friends who have the equipment to check frequency, impedance and transmission power of the modules, antennas and cables at work and I could give some stuff to them to make some measurements but I always have to select my stuff well, because they also don't have infinite time at work Smile

Best regards,
engolling
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#7
I think you will find this very interesting:

https://goughlui.com/2016/05/01/shootout...-compared/

A few things to consider (in my opinion):

- First of all, beware of local regulations on 433Mhz. Amateur operators are right there in that "neighborwood", and will be pretty easy to annoy someone IF you have an operator near you.
The fines can be a bad surprise if your regulator decides to pay you a visit.
I'll bet that almost every TX modules are "illegal" because of the chinese frequency stabilization and in other cases, the output power. The good thing is, those frequencies are not that populated and I think that almost no one will ever notice those tiny TX pcb, anyway, be mindful.

- Like Werk_AG said, sometimes the module will perform worse with 12V than with 9V, will heat more and probably will fail sooner.

- Also like Werk_AG said, some modules will change TX frequency by changing the voltage

Meanwhile, I invite you guys to check this:
http://www.image.micros.com.pl/_dane_tec....1-433.pdf

Like you will see, those RX modules will tipically work between 433.82 and 434.02 Mhz.
I saw TX modules transmitting outside those freqs - in 434.90 for example, so, going up on the power does nothing besides making higher the risk of RF polution and RX saturation
In the older TX modules (those with two small coils), even the antenna lenght could change the frequency ... by the way, those coils can be used to "tune" the frequency.

- If I was you and if possible, I would check thoses frequencies, then I would insist first on the TX antenna, second on the RX antenna, third on TX antenna and forth on RX antenna, at last, I'll check the RX antenna one more time just in case Wink

I tried several antennas and modules and can say for a fact that the modules, even if they are alike, same model etc etc, they can perform different.
I found for example two equal modules, bought on the same seller with almost 1Mhz difference on the frequency. Altough RX module is sensitive, that can add some surprises to the end result.
One of them was transmitting way outside of RX range, so, I had almost nothing received on RX when using those specific module, when I changed by the equal brother, voila, everything was good to go.

Some time ago, I made a few tests and after measuring the right frequency and trying some different antennas, I can say that I managed to receive the TX signal from about 1 KM from it. Yes, it was on a relative open space with a few houses and trees along the way, but, the signal was there without any changes on the power.

- Like Werk_AG also said, is better to use the antenna right on the SMA plug not using coaxial cable, the less the better, in fact, the best results I ever had was with the antenna directly on the module bypassing the SMA plug, oh, wait, with so many tests my TX PCB does not have any module soldered, it's "hanging" with cables to connect the module to pcb and making life easier when I remember to test something different on RF Smile

Sorry for the long post but I felt I have to say something about this.
My final advise is, power can help but isn't everything Wink
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#8
I would like to add that MeteoEstarreja is our RF expert, he is a Radio HAM with many years of experience, having collaborated in many projects of communication networks in Portugal.
For my great pleasure he also is a member of the WeatherDuino Test/Development team since the beginning of this project, which started five year ago.
He did the first tests of our system in what he called an "RF storm ambient" Smile
MeteoCercal - Air Quality Data
Click here to watch at my ThingSpeak channel



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#9
Hello meteoestarreja,
thank you for your very informative and detailed feedback. I appreciate that you took the time to share your knowledge.

So taking your answers into account we have to confess, that it's more or less random how the frequency of the resonator is tuned and shifts with voltage in addition to the sensitivity of the receiver.
In summing up the best would be to match transmitters and receivers.

Concerning the topic with the bad reception when using a wire this should also be investigated. Taking into account the free space attenuation i have path loss of 63dB ideally bridging 100m and in 100m RG58 wire I have a path loss of 40dB. So this must mainly be a effect of the connectors.



Back to my question - the transmitter I linked should work basically (if it is tuned right), or does anybody have some constraints?

Well I will have to get a variety of different transmitter types, build a test setup with adjustable transmitter supply voltage, motivate my friends  Wink  and do some measurements of output power and frequency.
Maybe I can do this around Christmas time  Smile 

Meanwhile I will try to get along with the current situation, because it might be ok, when aligning the antennas properly. But nevertheless I'm taken by that topic.

Regards,
engolling
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#10
Hello engolling,
no need to thanks, that's why I'm here, it's excelent when I can give a little of my knowledge and at the same time, take so many from you guys, I think that's the hole ideia of sharing.

So, honnestly, I already tested dozens of those tiny transmittors and I'm not saying that it's completely random to get a "good" one, but, it's true that I tested some weird ones even from the same batch.
Depending on the models it's even possible to "tune it" and solve the deviation problem, if you have no chance to test it with some kind of equipment, I suggest to use something like hornychz used, an RTL SDR.
With a cheap dongle, you can use a raspberry or a computer with sharpsdr for example to get an ideia of what is going on with your transmitters. It won't help that much about power measurement but definetly will help about frequency deviations, bandwidth used, RF saturation and easely check if input voltage will shift the frequency for example.
In the first use of the dongle probably you will have to calibrate it, but that's easy if you pick a signal that you now for sure it's frequency, preferrably a signal with narrow bandwidth and near from 433Mhz.
With this you can even test several locations and have an ideia wich ones are better for your purposes.

If I may also suggest, if coaxial cable is needed, you can use a (much) better one, other than rg58. Start with LMR cables for example, to get an ideia, check this small table
https://en.wikipedia.org/wiki/Coaxial_cable
you can even find better tables with much more data on it, this is just a start
Another thing that would help, is using a diretional antenna instead of an omnidirectional one, that ensure that almost every energy is directed to the right spot.

I hope that this would help
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