Jumper 4in1 Range Check

[Gary Manuel]

Hi.

I'm in the process of transferring all my models across from my JR DSM2 transmitter to my Horus 12s running OpenTX 2.2.4 and fitted with a Jumper 4in1 module - in serial mode. Everything is going to plan, with every module so far binding first time to my existing DSM2 receivers, straight from the Horus "bind" feature in the setup menu.

The question I have is one that I've not been able to find by googling etc, so I'm hoping that someone on here will know. How do you range check the model when using a multiprotocol module?

The Horus has a "range" feature in the setup menu, but I'm not sure whether it actually reduces the power output of the external module. The DSM2 receivers do not have telemetry, so I can not use the RSSI value to check.

[John Wagg]

I presume the receivers have an indicator LED.

Place Tx in an appropriate position and then walk with receivers until receiver LED alters (starts flashing or whatever?) indicating loss of signal.

[Mike Blandford]

As long as you are using serial mode to the MPM then the range feature will reduce the output power.

Mike

[Gary Manuel]

Thanks Mike. That's what I was hoping.

John. I needed confirmation that the transmitter was on reduced power output whilst actually doing the test, otherwise there's no point doing it. I'll walk away from and around the model whilst wiggling the sticks like I normally do, now that I know the power is reduced.

[Peter Christy]

One thing I found with my IRX module (similar, if not identical, to the Jumper) is that when using Orange DSM-X receivers, I was getting RSSI warnings when there was still a very acceptable signal level.

Its something that I need to look in to at some point (not high on my priority list at present!), but the level necessary to trigger the warning is clearly different between DSM-X (at least, the Orange version) and FrSky.

--

Pete

[John Wagg]

Posted by Gary Manuel on 27/02/2020 07:49:40:

Thanks Mike. That's what I was hoping.

John. I needed confirmation that the transmitter was on reduced power output whilst actually doing the test, otherwise there's no point doing it. I'll walk away from and around the model whilst wiggling the sticks like I normally do, now that I know the power is reduced.

The one main reason for walking with the Rx is that if it doesn't have telemetry that you won't get RSSI readings on the Tx. But as the LED changes you will get positive indication of signal.loss.

Yes it's a lot more practical if you reduce the Tx power.

[Gary Manuel]

Posted by Peter Christy on 27/02/2020 08:59:13:

One thing I found with my IRX module (similar, if not identical, to the Jumper) is that when using Orange DSM-X receivers, I was getting RSSI warnings when there was still a very acceptable signal level.

Its something that I need to look in to at some point (not high on my priority list at present!), but the level necessary to trigger the warning is clearly different between DSM-X (at least, the Orange version) and FrSky.

--

Pete

Peter.

I have an Orange R810X receiver that behaves similar to what you are describing. It gives warnings of loss of telemetry etc, so it must be transmitting something back to the Tx.

I've tried to display the RSSI value, but all I can see is the TRSS value. As I understand it, RSSI is the Received Signal Strength Indicator, giving a measure of the signal strength seen by the receiver. The TRSS on the other hand is the Transmitter to Receiver Signal Strength as measured by the Transmitter. As the Receiver transmits at a much lower signal level than the transmitter, the TRSS is bound to be much lower than the RSSI. I have seen somewhere that RSSI is 3x the value of TRSS and if you want to use the warnings, you should divide the warning levels by 3 (i.e. 14/15 rather than 42/45). Don't quote me on that or rely on the warnings, but that may explain the behaviour you are seeing.

[Gary Manuel]

Correction - abbreviation TRSS = Telemetry Received Signal Strength.

Also my receiver is an R820X v2.

Edited By Gary Manuel on 27/02/2020 10:49:11

[Peter Christy]

Thanks for that, Gary! It does sound about right. If the weather ever does finally improve, I'll do a ground range check and work out the indication at which signal is actually lost, add a safety margin, and then use that figure when setting up DSM-X stuff.

The built-in figures for FrSky receivers seem to work OK. I've never had a signal loss with FrSky, but do get the occasional warning when the antenna orientation is less than ideal. This is something I would expect at these frequencies! With the DSM-X, I was getting near constant warnings, despite never actually suffering a loss of signal. It was quite irritating!

As I say, not at the top of my list at the moment, but something I will look at in due course....

--

Pete

[Gary Manuel]

Right, I've done a bit of experimentation in my back garden and have found a few useful facts that I'll share as they may be of some interest.

1. Range check definitely reduces the output power . I can "Force" a loss of signal to the Satellite (light goes out) Receiver (not the main receiver which has 2 diverse aerials) by separating the transmitter from the model by about 25m and pointing the transmitter aerial directly at the model. Model is still under control though because the main receiver never loses the signal. I would need to walk further than the length of my garden to lose control, so I'll do this at the flying field. When I move the transmitter so that the aerial is not pointing directly at the model, the satellite receiver recovers. Similarly when transmitting at full power (not on range test), full signal is recovered.

2. TRSS is definitely the signal level from the receiver as received by the transmitter. It does not change in value when performing range test - the reading is exactly the same, even at the point when the satellite receiver light goes out on range test.

3. The Horus "RF Signal Low" and "RF Signal Critical" alarms occur with the transmitter held at the same position, whether the transmitter is in range test or not. This suggests that it is actually using the TRSS signal as it's source. The TRSS value is around 14/15 when this occurs, even though the alarms are set to 42 and 45. The gauge on the Horus screen is also showing full strength when the TRSS value is around 30 (i.e. well below the set critical value). The Horus is not therefore using the actual value of TRSS value as a direct substitute for RSSI.

4. When in "Range Test", the Horus displays a RSSI value. This is EXACTLY 3 x the value of TRSS. It follows therefore that the Horus (or rather OpenTX) must be clever enough to know the difference and multiply the TRSS value by 3. Note that the suggestion in one of my earlier post of resetting the alarm values to 14/15 looks wrong because of this. I'm not convinced that leaving it as 42/45 will work but I'll have a play round if these values are too sensitive.

5. Because the TRSS is not the same, or as useful as the RSSI it must be used with caution, but may still be useful for indicating when the limits of range are being approached.

6. The value of TRSS is quite meaningless when displayed on the screen, but a value of (3 x TRSS) would be handy as it would correlate nicely with the gauge and alarm activation. Displaying it as RSSI would be confusing and incorrect though. I've set up a widget to display "3xSS" on the top bar as follows:

This was the TRSS sensor - renamed to "3xSS". Units changed to "dB". Ratio changed to 768 (3 x 256 which gives a factor of 3).

Widget created in the top bar, using the newly created 3xSS as a value. It displays the TRSS value multiplied by 3 with "dB" as a suffix. Not displaying properly on simulator for some reason, but it works on the Horus.

Edited By Gary Manuel on 27/02/2020 12:59:56

[john stones 1 - Moderator]

I love to see a man happy in his work, you're enjoying it then Gary.

[Gary Manuel]

Posted by john stones 1 on 27/02/2020 15:21:35:

I love to see a man happy in his work, you're enjoying it then Gary.

Certainly beats the alternative.

Mrs reckons RSSI stands for Rinse Soap Suds Incessantly.