[werk_ag]

By the way, try with 16cm and not 18cm since it's near from 1/4 wave length for 433Mhz (if I was not mistaken in calculation, the best measure should be 16,5 cm). Being that "far" from the right value, will affect specially RX like you're experiencing.

Theoretically those modules are 433.92MHz which leads to a 1/4 wave antenna with 17.3cm, but using SDRSHARP I saw that the frequency is normally below that value, around 433.7Mhz.
I don't know about SDRSHARP precision, so this value may not be exact.

[meteoestarreja]

Theoretically those modules are 433.92MHz which leads to a 1/4 wave antenna with 17.3cm, but using SDRSHARP I saw that the frequency is normally below that value, around 433.7Mhz.
I don't know about SDRSHARP precision, so this value may not be exact.

In fact while testing it, in some cases I saw a small deviation on frequency.
You can calibrate SDRSHARP, using a transmission that you know for sure the frequency, like an ordinary FM broadcast radio or a ham repeater (you will find some very close from our station TX frequency) and adjust the value on the software so the frequency meets the frequency that you already know.
About the antenna, how did you get the 17.3 cm value? From my calculation, 17.3 would be somewhere around 428,3 Mhz
Also, do not trust 100% antenna's size from the outside plastic, I encountered several antennas with a outside size, and the antenna inside the cover had smaller size

BTW, the project - when/if it came to day light - will not use any usb dongle, the parts needed will be all together on pcb.

[werk_ag]

About the antenna, how did you get the 17.3 cm value? From my calculation, 17.3 would be somewhere around 428,3 Mhz

Of course you are right about the value of the 1/4 wavelength for a 433.94MHz frequency, where l= c/f
l = wavelenght
c= speed of propagation (usually light speed)
f = frequency

but some time ago, using Google I found several references to a formula to calculate the length of single wire (whip) antenna.
The formula is: 75/frequency(MHz) = length in meters
which for 433.94MHz, results in a whip antenna length, of 17.28cm
Certainly you could investigate about this matter

[meteoestarreja]

My dear friend, now I understand your measures
I think that you should use this formula only when using a ground plane (that you're not using with a single wire).
Without it, I'm not sure that the formula shown by you should be the most appropriate.
Anyway, I'm curious about using whip calculations for a single wire (without ground plane) and I will do some research/simulations later today (I hope).
When I have some results, I'll share with you guys

[werk_ag]

I think that you should use this formula only when using a ground plane (that you're not using with a single wire).

There isn't a way to cheat you not even a little, isn't it?
That's right, that formula aplies to whip antennas with a ground plane.

When you have the time, maybe you could post something about what is a ground plane, I would like the learn something about it.

[werk_ag]

Werk, I first noticed the problem with the antenna when it was actually outside (5-10 metres away through a couple of walls). Where my 16cm length of wire is usually used with good results.

Do you have connected a small SMA pigtall to your TX module?

[uncle_bob]

Do you have connected a small SMA pigtall to your TX module?

Yes, Werk, I do. Note that I've also got a small piece of fishing line support the wire in the left top of the FS1000A

[hvalentim]

since you're testing just with a fence wire, you could forget about GND for now, since using just a simple wire, you must connect it, to the ANT pin and nothing else.

OK. Thanks for the explanations.
Once I receive the proper SMA antennas should I connect one of the GND pins (I guess the one next to the ANT) from the module to the external 4 pins of the PCB SMA connector (just for testing sake)?

By the way, try with 16cm and not 18cm

Does not seem to help. Also changed from fence wire to copper wire from TV coaxial cable and it does not seem to improve.

The curious part is that without anything working as an antenna, just a couple of centimeters (more than that it does not work) away from each other, the lower quality XD-RF-5V /FS1000A couple seems to produce a more steady result. I mean the RX signal is constant.

With the 3400 RF Kit, while TX remains constant, on the RX side I get something like 5-10 constant receptions, one (very) slight pause, another 10 constant receptions, one (very) slight pause....

It may be somehow related with software and the Virtualwire library. Also, it crossed my mind that such a thing as a "minimum distance between the TX and RX antennas working at any given frequency" must exist!? I am keeping them just 4 cm apart, which does not seem right. I need a second test board so I can separate them a few meters and simulate more real working conditions.

The point being making sure all parts are in good working order before any soldering begins.

BTW, while at it, I noticed that when the RX module alone is ON I pick some noise on the portable radio. I also noticed that TX seems to be best picked by the radio at around 434.005-15. Another thing which I am sure some principle of radio propagation may explain is that as I walk further away from the TX the signal seems to be better received on the portable radio at an incrementally slightly higher frequency....

About the second question and without using additional hardware, I'm not imagining an arduino measuring signal strength at least with accuracy.

It seems a few 433Mhz modules used with Arduinos include RSSI, which is not the case. Somewhere (I am afraid I lost track of the link) I also read about a procedure with code which seems to make sense: a simple test of the TX/RX link can be achieved by systematically sending a known number of packets in the TX and then count exactly how many were received and or lost in the RX.

You could try for example use a "special" TV dongle (you can find it very cheap on ebay) and use SDRSHARP with it.

Yes. I have heard about those before. I do have an USB TV-Radio dongle (Avermedia) but it does seem to have a supported chip. I have to persuade myself to buy another. I believe Box-Jumbo/Auchan sell a cheap OEM model which judging by the looks should be compatible. I will try to check next time I go there.

[hvalentim]

Learning along the way.

Having purchased myself one "433MHz GSM GPRS 90° SMA male plug right angle 10cm Ham radio Gold" antenna I disassembled it.

It turns out it uses a 2,5 cm helical. The additional 7,5 cm of void space inside the plastic cover are used for... well Feng Shui purposes. They should be harnessing Chi.

   

[werk_ag]

Do you have connected a small SMA pigtall to your TX module?

Yes, Werk, I do. Note that I've also got a small piece of fishing line support the wire in the left top of the FS1000A

According to info from uncle bob, the problem was solved, just by resoldering the central antenna wire through the hole in the TX module. This info may help others.