A question to AndyK or radio gurus

[Flying Scotsman]

Andy, you are a bit of a genius on FE matters. I am still mulling over the pros and cons of 2.4ghz over a synthetised FM system. I use a Hitec CRX with Spectra and have had no issues. Most of my boats (9) run on a different rx crystal. If I went with 2.4ghz would I obtain a stronger and less glitch prone signal as I am presently using almost the full bandwith of 75mhz?

Douggie

[AndyKunz]

I went with Spektrum on my planes because I didn't feel like waiting for frequency pins when I go to places. Last year (2007) we got 3 flights in because the flight line and frequency board was so busy. I was at a meet this year and only 1 guy was on 72MHz. It was a lot nicer for everybody. (I had a Hitec Spectra module - but I wasn't about to open planes to swap xtals. We have one more Spectra for sale with a bunch of Rx's if anybody is interested).

For surface I went with Spektrum because "I can." I didn't have a tecnical need. I really like not having to put a huge antenna tube out in the wind. I've seen firsthand how that kills speed. My old N2 rigger now has a 6" tube instead of an 18" one - much more convenient and less wind resistance.

The other BIG feature I like about Spektrum, and Futaba DOESN'T have it (Spektrum patented it) is Model Match. If you're running 9 boats, you really ought to consider Spektrum just to keep from running the wrong setup. While it's not as important in a boat as it is in a plane, it has saved me a couple times (I set up the boats with asymmetrical steering and trims).

Are you having problems now with glitching? If so, are you using a DCX rx? They really are the cat's meow for FM systems. Going to Spektrum would likely solve your problem if it's an RF issue. For a lot of guys, the BEC has been the problem. Spektrum is better in that regard too, because they are designed to allow operation at lower voltages.

FWIW, I have seen complaints about range problems on the water but have not experienced them myself. I didn't have problems with my boats on FM either, though. Just the other day I had my N2 boat about 600' away and I was standing on the opposite shore w/o a problem (other than shivering). I am running a DX3R with a variety of rx's both DSM and DSM2.

Hope this helps. If not, keep the questions coming.

BTW, you don't need to upgrade to a DX3R to go 2.4g. I think Spektrum has a module that will plug into your radio. I had a SPMFUT7 in my Hitec Eclipse 7 transmitter. There should be a drop-in for you.

Andy

[AntronX]

Why not run all of your boars on one frequency? Choose one channel in your area and make it your own. If your FM setup is working fine, then why change it? If someone got stock AM 27Mhz, then 75 FM or 2.4 DSM will be much better. I went from 27 AM to Futaba 2.4 Ghz and no more servo glitching.

[AndyKunz]

I think this is the module for your tx.

http://www.horizonhobby.com/Products/Default.aspx?ProdID=SPM1114

Note that you lose Model Match with a module system, but like I said, it might not be really important in your boats like it is for a plane.

Andy

[Flying Scotsman]

Yes Andy, I am using DCX rx. It was more of an issue on perceived problems on using the full bandwith of 75mhz with a synthetised signal.

Douggie

[Flying Scotsman]

Why not run all of your boars on one frequency? Choose one channel in your area and make it your own. If your FM setup is working fine, then why change it? If someone got stock AM 27Mhz, then 75 FM or 2.4 DSM will be much better. I went from 27 AM to Futaba 2.4 Ghz and no more servo glitching.

Anton, the reason I went with the Hitec Spectra system as you can change a frequency that will not clash with other users. I use a device that will let me know who is on a certain frequency

Douggie

[AndyKunz]

Yes Andy, I am using DCX rx. It was more of an issue on perceived problems on using the full bandwith of 75mhz with a synthetised signal.

I think there's a little misunderstanding.

Your Spectra module doesn't use any more or any less bandwidth with the same number of channels (2 or 3) than any other AM or FM system on 27, 37, 39, 49, 50, 53, 72, or 75 MHz with that number of channels.

It only gives you the ability to use different 20kHz channels more easily. It's no different than swapping xtals - you're just doing it electronically. (The 20kHz varies a little depending on carrier and country).

That said, the 2.4 spectrum is broken down into 80 bands of 1 MHz each, and each one of them can pump a huge amount of data down the 1M channel. With a 2.4 system, the transmitter is (at one instant) only transmitting a short burst in the 1 MHz frequency (it is also NOT transmitting a whole lot larger part of the time - this is called the "duty cycle"). How they do that, and what the data looks like, varies from manufacturer to manufacturer.

The end result, though, is that the same amount of functional data (a frame) gets from point A to point B.

The DX3R has several possible frame rates, selectable by the user. You can vary it depending on the kind of driving you do, but for a boat the standard 22ms (same as PCM) data rate is sufficient.

If you're counting on a bigger bandwidth to help you, you're not understanding. There are some great explanations out there on the web, and there are some very BAD ones out there too.

I guess it still comes back to the question, Are you experiencing glitching? If so, what is the source? 2.4 is immensely more immune to the sorts of RF issues that we had with AM and FM systems on 27/75.

Andy

[Flying Scotsman]

Andy, dumb Douggie. I was using the expression of bandwidth in regards to the available frequences in the 75mhz. If, I use a Spectra system am I limiting the tx and rx in regards to sensitivty on a given frequency. In other words would a dedicated tx and rx perform better

Douggie

[AndyKunz]

No, they are going to perform the same whether you use a Spectra or a crystal FM module or a 2.4g radio. You can safely operate simultanteously 80+ systems on 2.4g, and 30 on 75. It doesn't make a difference.

The big feature that makes 2.4 the technology of the future is that they don't interfere with one another. In standard ("antique" in my opinion) equipment, there was no protection if somebody was on the same frequency as you. With 2.4 they automatically seek an unused frequency, but even if they end up sharing a frequency you still have a code word (called the GUID) which is used to link a particular transmitter and receiver together.

Andy

[supafastsupra2]

you can also use the FASST system for the Futaba 3PK on your radio. It is a more reliable signal than the DSSS style systems.