botched antenna mod, need new RF9x-v2

[Tizzy]

Hi people,
Finally the wind dropped enough today to get some flying in and try out my new 5db antenna. I had removed the original antenna a couple of weeks ago and added a few SMA connectors in between the original location and the RF9x-v2 module so I could easily swap out modules if needed. I haven't got any other modules yet but I was hoping I'd get some extra range off the new 5db antenna and large was my dismay when failsafe set in at about 5meters. On checking I found there was no resistance to be measured on the PCB between grnd and the coax positive, even after I'd unsoldered my connections. I believe I fried the module when I removed the original coax as the connections weren't easy to unsolder and I had to turn up the heat, I tried to be quick but obviously I wasn't quick enough. If anyone has a good idea on how I could fix it, I'd be mighty interested. Otherwise I'm looking for a new RF9x module or just the innards.
All input is welcome and thanks in advance.
Cheers
Rick

[Rob Thomson]

You using a stock 9x antenna module?

I just happen to have circa 6 of them in a box!

PM Me your address and I can send you one for the cost of the postage!

[Tizzy]

Wow, that would be great. How do I send you my address? I don't see any PM option..

[Tizzy]

Don't know if it's me or something to do with the fact I'm relatively new here, but my posts aren't showing up right away or maybe at all, so forgive me for doubleposting if they do happen appear in a while.

Thanks for offering. I am using the stock module altho it says V2, so not sure if a v1 will work out of the box? I'm definitely willing to try of course and would be much obliged. I'd rather not post my address in public but I also don't see a PM button anywhere. Perhaps I should just wait a bit as my chat's don't seem to be getting through either, I suspect it's an antispam thing?

[Crucial]

It's because you're new. I think you should be all set with your number of posts.

[Tizzy]

I was still hoping to get my antenna mod going but before I got around to taking apart a new stock FlySky module (thanks Rob!) I came across someone who had a spare rf module (thanks Kaos!) that I could hook up to my existing button board. So I decided to keep the new module whole in case things went wrong again. But because the weathers not been good enough to test it out, it's just been lying there while I waited for something to change.

And then I got the rf module yesterday and managed to solder it quite easily to my button board. But to my surprise there was still no resistance to be measured between the coax positive and grnd. So I checked the (unmodified) FlySky module and to my increased surprise it too showed no resistance between grnd and positive. So I then checked the FRSky DJT and it does show resistance between the two poles. I thought that perhaps the stock module needed power but even then there's no resistance between the coaxial center pole and the external grnd.

What's going on? Can someone please verify with their FlySky module whether it's supposed to have resistance or whether they're all like mine?

[jhsa]

I just measured the one I took from my new radio when I installed frsky and it does show resistence.. about 0.1 ohms or so..
I remember that with my old one that now is installed inside an old graupner MC-16 it was the same, I thought the module was broken but it's still working..

[Tizzy]

Yep, that's pretty much what I get on the FlySky but the DJT has infinite resistance so I'm confused, how can the FlySky work like that? And is that the reason my 5db antenna didn't work in the first place?

[Kilrah]

Depending on RF circuit design, an antenna output can look open or "short-circuited", that won't mean anything. A direct current short circuit can be perfectly open at radio frequencies.
By the way one should never measure an antenna port with a continuity tester. In addition to giving no useful information, depending on design that can also damage it.

[jhsa]

oooppss, I just did it... Thaks for letting us know that.. I didn't know it..

[Tizzy]

Depending on RF circuit design, an antenna output can look open or "short-circuited", that won't mean anything. A direct current short circuit can be perfectly open at radio frequencies.
By the way one should never measure an antenna port with a continuity tester. In addition to giving no useful information, depending on design that can also damage it.

Thanks, that gives some comfort. I'll have to do some more testing then to see if the 5db antenna works now with the new mod and if so, I did indeed fry something previously, just not the coax connection..

Indeed Oops. "continuity tester" if that's the same as a (digital) multimeter how would I test if it damaged anything other than finding out in practice that I have no range?

Edit:
While I'm at it, how do I range test the FlySky module?

[Kilrah]

AFAIK to range test you're supposed to hold and maintain the button on the module for all the duration of the test. That doesn't seem very documented though, that's all I found the other day after a rather long search.

[Crucial]

It's been long understood that the bind button on the flysky module does not function as a range test.

[jhsa]

get yourself a friend with a car (better a good car like a porche or something), and use it to drive away with the transmitter while he holds the model.. you should have a ride of about 500 metres or so. could be intermitent depending on obstacles

EDIT: maybe better he drive away with the radio and you hold the model, so you can see when controls stop moving..

[Tizzy]

okay, so it sounds like the best option would be to test my drone in the field without an antenna fitted until it failsafes, and then switch between the stock 2db antenna and the new 5db one. I'll post back if it first of all works and secondly, if it does makes a difference... Thanks so far.

Edit:
just missed the post on the porsche, indeed sounds like a way better option.

[ShowMaster]

My 2 cents.
Rf is AC and is measured in impedance(AC resistance),resistance in DC is also measured in ohms but a DVM can't measure impedance.
An rf circuit at resonance can be very high impedance but a short to ground DC wise. Many mountain top antennas take advantage of this in the fact that at the tx frequency the antenna is 50 ohms impedance at the frequency it's tuned for but a direct short to ground to lightning that's a DC static pulse. This saves the equipment from damage usually.
So as good as a DVM is it's pretty useless for troubleshooting rf circuits.
BTW since RF is AC it can pass thru capacitors in series with the antenna and the DVM will show an open "DC" resistance that is not so when the circuit is actually powered and working.
Antennas and RF is really magic stuff and thats why ham radio requires a better knowledge of it to become licensed.
Finally ,
I'm going to take a new FlySky stick TX into the RF shop at the studios today when I go in and see what a Spectrum Analyzer says about the bind button and RF output level to get the real deal answer to what happens if pushed or held in?
Then we'll all know for sure.


ShowMaster
Sent from my iPod touch using Tapatalk

[Tizzy]

My 2 cents.
Rf is AC and is measured in impedance(AC resistance),resistance in DC is also measured in ohms but a DVM can't measure impedance.
An rf circuit at resonance can be very high impedance but a short to ground DC wise. Many mountain top antennas take advantage of this in the fact that at the tx frequency the antenna is 50 ohms impedance at the frequency it's tuned for but a direct short to ground to lightning that's a DC static pulse. This saves the equipment from damage usually.
So as good as a DVM is it's pretty useless for troubleshooting rf circuits.
BTW since RF is AC it can pass thru capacitors in series with the antenna and the DVM will show an open "DC" resistance that is not so when the circuit is actually powered and working.
Antennas and RF is really magic stuff and thats why ham radio requires a better knowledge of it to become licensed.
Finally ,
I'm going to take a new FlySky stick TX into the RF shop at the studios today when I go in and see what a Spectrum Analyzer says about the bind button and RF output level to get the real deal answer to what happens if pushed or held in?
Then we'll all know for sure.


ShowMaster
Sent from my iPod touch using Tapatalk

Great stuff, will keep my eye open for your update!

[kaos]

the most accurate way to do range test:
put your full house FPV OSD with GPS and pan/tilt cam with head tracker and fly that plane straight out and watch the OSD distance, just enjoy the view while flying by panning/tilting the cam. once you see that cam is not moving anymore, you can read the exact range +- 3 meters you have with that Tx/rx.

[Hippo]

I didn't see it mentioned yet, but don't ever run 2.4ghz transmitters without an antenna attached. You're asking to burn something out if you do.

Trust me. Learned the hard way, then got scolded for it later to add insult to repair bill.

Dan

[ktgohdt125]

Hi, Tizzy and fellow 9x owners,

i have the same symptom like yours with the unmod & standard firmware flysky 9x TX, i manage to get in control around 30 meter on ground test only!! if more than 30 meter, servo start to get unresponsive & most of the time no movement.

i have also open up the Tx & Rx to check the antenna cable for cold joint but it all checks out with good solder connection!

Like u, i have also check the Tx & there was no resistance to be measured on the PCB between grnd and the coax positive, even after I'd unsoldered my connections. But on Rx, i have a very high resistance reading.

So, my question is, have u found your solution or repair the Tx module? if yes, can u share / teach me how to repair this 9x tx.
best regards
ktgoh
From Malaysia, KL

[C.João]

relax people! the stock 9x module has a "balun" circuit (transformer) that will filter some out-of-spec frequencies in and out of the module. that balun will "look" to be a short circuit. it actually is not.

frsky does not use this and it uses a software filtering. so it can be actually better (it the FW works out right).

probably you won't get a 9x stock module working right on anything else than de stock 2dB antenna... the balun does not alow that to happen properly. it is a tuned circuit.

[msev]

Joao so it won't work if I for example connect a coax+rp-sma to the pads on the tx module and then connect the frsky 7db patch to it?
How would I have to do it so that it would work optimally?