Spectrum analyzer picture of the 14mz changing the rx freq.

[tkilwein]

Can you guess what this is a picture of?
This was taken off the 14mz.

This is the 14mz tx sending the channel info to the RX to change.
channel assigned prior to power off - on was 38.
new channel is 41 being programmed in.

The power of the 14mz TX during this freq change is very low compared to when it is transmitting--- you are flying.

Looks like they use channel 11 to do the freq change.
when doing a test of a 9zhps on 11 doing a servo test and the 14mz doing a freq change caused no problems with the 9z doing a servo test in ppm
and pcm modes. the radios where ~20ft apart.

test setup

127 and 149 futaba receivers ~30ft to 9zh on channel 11 ~20ft to 14mz doing a repeat freq change ~1ft to 5014RX doing a freq change.
The 9z was doing a servo test and the 14mz was doing a freq change.

This caused no problems on the 9z and rx set and the 14mz was also able to change the 5014 RX with the rx and tx 1 foot apart. repeated this 3 times. The 5014 RX has the short antenna.

I will do a full freq scan to see if this is true and I was not fooled by some means. I will repeat using different freq selections. This will take some time.

I will check sideband freqs also. The above was a quick look.



Tony

[R-4-L]

im lost, what does it mean?

[kgfly]

Well it looks like a spectrum analysis of the 72MHz carrier from your Tx.

The traces indicate that the carrier is centred at 72.010019 MHz which is channel 11 (nominally 72.010MHz). I believe this is the first (lowest frequency) RC channel in the 72MHz band (see here: http://www.fatlion.com/sailplanes/freqs.html).

The adjacent channel is #12 at 72.030MHz where it looks like there is a small peak about 25dB down.

I am not sure what the adjacent channel interference specification is for RC so I cannot tell if this is showing a problem with the Tx or how good it is :dontknow

[tkilwein]

this is a picture of the 14mz sending the info to the rx to change freq to channel 41 when on channel 38 previously.

[kgfly]

So I was completely wrong :oops:

Oh well, at least I tried, can't resist a challenge :)

[tkilwein]

The 14mx TX power output is very low so as not to interfere with someone on channel 11 flying. This is why it needs to be very close to the rx to communicate.
The sniffer probe is uncalibrated so dB readings are off.
I plan on having my 9zhps on 11 about 30 feet away and do a freq change on the 14mz and see what happens as a test only. I have had very good luck with my 14mz and happy with it. this is all just curosity on my part.
Next is find out the BFV voltage trip level.

[rkeith2]

80 db down, no wonder fluorescents kiil the signal.

[JetCopter]

It is interesting to learn that channel 11 is what is used to perform the freq. change. I had a 5014 Receiver that would ONLY change to channel 11, and I always thought that was weird. In retrospect, I think it was probobly tuning to 11 in response to a ping from the TX, and never capturing the data to assign it to a new channel. Threfore, when I was selecting 11, it didnt matter because it got left on the channel I was transmitting on! I wish I knew this back then, I would have done some more testing.

[RCfan]

Ch 11 is the lowest channel on the US band. Rx was probably chosing a default when it couldn't get the ch.

[tkilwein]

From what I can tell the RX looks at chan 11 first on power up, if not getting the change info-transmission on chan 11, it then switches to the last good channel assigned in it's flash memory. This is why the RX is turned on last.

Tony