I'm working in 868 and 915MHz frequency bands for LoRa modulation. The problem i'm facing is variable current consumption by different antennas (having same design parameters) at same frequency and air rate. This is happening only at transmitter side. Due to this i'm getting variable communication signal range. I'm unable to come to conclusion because of this. If anyone who are working with RF or LoRa can suggest some solutions it would be beneficial

 

It sounds like you are using antennas that may not be a good match to your transmitter for some reason and as such mismatch and reflections may cause the variation in power/current. What do you mean exactly: (having same design parameters)?

 

It sounds like you are using antennas that may not be a good match to your transmitter for some reason and as such mismatch and reflections may cause the variation in power/current. What do you mean exactly: (having same design parameters)?

Mainly centre frequency, VSWR, antenna gain, impedance of antennas used. The LoRa module is connected to antenna via a UFL connector having IPEX and SMA connectors.

 

How are you measuring antenna current consumption? It appears to be a dubious concept.

 

You may want to consider using a Helical-Antenna, ( much better Gain too ),
or other Broad-Band-Antenna-design.

If You are attempting to use a Printed-Circuit-Antenna, there's the problem,
they are very "fussy", about everything.
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How are you measuring antenna current consumption? It appears to be a dubious concept.

While I'm pretty sure the OP is talking about module current consumption changing due to poor antenna matching, we had methods to actually measure antenna current.
A current probe can be a simple single loop to measure the magnetic field while the voltage probe can be a simple plate for the electric field measurement.
We used things like this for old school measurements with a calibration table.

 

Operationally, what you care about is effective radiated power. I'm just saying we never measured just the current for that purpose and I'm not even sure what the measurement would tell you. You can easily measure return loss and that will tell you about the match between the transmitter and the feedline/antenna combination.

 

Operationally, what you care about is effective radiated power. I'm just saying we never measured just the current for that purpose and I'm not even sure what the measurement would tell you. You can easily measure return loss and that will tell you about the match between the transmitter and the feedline/antenna combination.

We had 10KW+ HF transmitters into quad HF multiplex tuners to long wire rope antennas that we used from 2-30 MHz (with lists of frequencies in that total HF band we could use based on propagation) so we monitored current as a indication of tuner coupling. Operationally, what we cared about was the signal quality on the distant end to the next ship or shack on a hill. Different worlds in tactical HF radio from most fixed stations with fixed frequencies/bands and antennas.

 

You may want to consider using a Helical-Antenna, ( much better Gain too ),
or other Broad-Band-Antenna-design.

If You are attempting to use a Printed-Circuit-Antenna, there's the problem,
they are very "fussy", about everything.
.
.
.

Actually using either Helical or any other Broadband antenna is not viable for my project hence I'm using a Dipole whip antenna.

 

While I'm pretty sure the OP is talking about module current consumption changing due to poor antenna matching, we had methods to actually measure antenna current.
A current probe can be a simple single loop to measure the magnetic field while the voltage probe can be a simple plate for the electric field measurement.
We used things like this for old school measurements with a calibration table.
View attachment 319663

Exactly, i'm observing current consumption of the system before transmission and during transmission. Fyi system consists of Rpi CM4, Rpi Pico and LoRa module.

 

Operationally, what you care about is effective radiated power. I'm just saying we never measured just the current for that purpose and I'm not even sure what the measurement would tell you. You can easily measure return loss and that will tell you about the match between the transmitter and the feedline/antenna combination.

Agreed with the statement that we care about effective radiated power in case of an antenna. However, the current fluctuation is an observation made during the process of testing the system. This current consumption value i think is directly proportional to the range i'm achieving between Rx and Tx. I'm using a fixed air speed and a set frequency of 915MHz throughout the testing process but still the ranges i'm getting on different day are different and the current consumption by the system on these days are also different.
Is there a way around to deal with the problem other than measuring return loss? If there are no other way then I have to work on setting up things to measure return loss.

 

All these current variation chaos is happening only when an antenna is connected to the system. Without antenna connection every single copy of the system is consuming constant current when in transmission mode.

 

The higher the Frequency, the more critical the Antenna "system" becomes.

It may be possible that You will get "satisfactory" performance just the way it is.

Change the Frequency = Change the Antenna.

Increasing the Diameter of the Antenna-Elements will make it slightly more Broad-Band-compatible.
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The higher the Frequency, the more critical the Antenna "system" becomes.

It may be possible that You will get "satisfactory" performance just the way it is.

Change the Frequency = Change the Antenna.

Increasing the Diameter of the Antenna-Elements will make it slightly more Broad-Band-compatible.
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thank you for your reply LowQCab but i'm not designing antenna. I'm using COTS antennas.

 

In that case You may be able to add some Tuning / Matching-Components,
but while this will usually result in a happier Transmitter,
it will also significantly sacrifice Radiated-Power,
and, the extra Components must be properly "Tuned" for each "Frequency-Range".

That's why I said that You may get "satisfactory" performance with everything "as-is".
It will never be "perfect".

There really is no "fix" for the "wrong" Antenna.
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Agreed with the statement that we care about effective radiated power in case of an antenna. However, the current fluctuation is an observation made during the process of testing the system. This current consumption value i think is directly proportional to the range i'm achieving between Rx and Tx. I'm using a fixed air speed and a set frequency of 915MHz throughout the testing process but still the ranges i'm getting on different day are different and the current consumption by the system on these days are also different.
Is there a way around to deal with the problem other than measuring return loss? If there are no other way then I have to work on setting up things to measure return loss.

In that frequency band I would expect propagation of RF energy to be affected by things that have minimal effect on HF signals in the 3-30 MHz. range. Humidity is a prime example. People who try to set distance records at various frequencies do it on cool dry days in the early morning for a reason. The use of rifle scopes to align directional antennas is also a common practice. I think the best you can hope for is high probability of successful communication at a given range. It might help you to research what the people trying for distance records are able to accomplish. This will aid you in setting your expectations.

 

Exactly, i'm observing current consumption of the system before transmission and during transmission. Fyi system consists of Rpi CM4, Rpi Pico and LoRa module.

I not surprised at the power changes due to changes in the RF link. LoRa IMO has very optimistic range specifications for low power. We had spread-spectrum radios in the late 70's they were pretty efficient on tx power but most transponder nodes were set to max power, I think LoRa is a basically a Pulsed FM (Chirp) spread-spectrum system.
https://wirelesspi.com/understanding-lora-phy-long-range-physical-layer/

I've not done a deep dive into the specifics of LoRa power management and control but in a low power link budget, the tx/rx antenna coupling while important, is a smaller factor in the total link loss than distance.



https://lora.readthedocs.io/en/latest/#range-vs-power

 

Some antenna constructions are drastically sensitive about gap length (as J-pole) or resonator length even in sub-millimeter scale (Yagi), or is heavily dependant on cable soldering point position and even tin amount in that, the same about cable sort, insulation thickness or balun wound count , diameter etc etc. I have rather much suffered at 868 MHz to know those antennas are much capricious and thats not so easy to produce it ideally identical at kitchen worktable obstacles. Thus, the good VNA is must to be. I would reccomend the PS102 or cheaper SA1201, but at sharp problem of money inflow may happen be enough even with NanoVNA.

 

I'm working in 868 and 915MHz frequency bands for LoRa modulation. The problem i'm facing is variable current consumption by different antennas (having same design parameters) at same frequency and air rate. This is happening only at transmitter side. Due to this i'm getting variable communication signal range. I'm unable to come to conclusion because of this. If anyone who are working with RF or LoRa can suggest some solutions it would be beneficial

You say you are using COTS antennas. To get an idea of what you might be running I took a look at the SX1262 LoRAWAN Node Module with CB antenna.

I have some questions the answers to which may help me to provide a solution.

1) Are you testing the different modules with the exact same antenna?

2) If not, can you provide the antenna model number(s) and how the antenna(s) is mounted?

3) How variable is the communications range (min and max distances achieved)?

4) What distance must be achieved for a successful product?

SX1262
https://www.pishop.us/product/sx126...-for-raspberry-pi-868-915mhz-gnss-cb-antenna/