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Spektrum DX7

Old radio?

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David Price 1128/07/2019 18:53:45
1 forum posts

Hi there,

I have been flying for many years, I passed my A cert on my 9th birthday and am now 35 haha. I have a Spektrum DX7 and just curious as things have developed so much in recent years if I'm best to buy a new transmitter?

I was flying regularly until about 3.5 years ago.

If recommend to replace it is the any recommendations from anyone?

Thanks

David

Chris Walby28/07/2019 20:14:42
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1004 forum posts
236 photos

Hi,

I have a DX8 gen 1 and it works okay + Al's Models can service it and make sure its okay and will probably include a firmware update as part of the service (did for me).

I bought a DX8 gen 2 as my gen one did not like lemon 6 channel RX's and it seems better, but I only trust it with very small foam models. Now the price of RX is back down to normal its not an issue.

DX8 gen one can do DSM2 and DSMX RX's, but all new TX will only do DSMX RX's

Just have to be careful with the second hand market as there are very poor copies out there (if the deal seems to good to be true, then it probably is!).

Main thing with the new TX's and RX's is that telemetry is built in..if you need it.

Denis Watkins28/07/2019 20:20:05
3914 forum posts
61 photos

Check this thread David about Tx change

**LINK**

Peter Miller28/07/2019 21:01:56
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10271 forum posts
1226 photos
10 articles

I bought one of the first Spektrum DX7s in the country, must be at least 10 years ago.

It is still my number one transmitter so why change?

In fact Ibought another when Horizon was moving so I ha a spare and I still keep that ready.

Trevor Crook29/07/2019 06:34:48
868 forum posts
65 photos

My DX7 is still going strong, original battery is even still good. I don't use it much now as I find my Gen 1 DX8 easier to program, and it will still work my DSM2 Rx's - I think later Gen 1 DX8's had DSM2 disabled.

As Peter says, if it still works fine keep using the DX7, it will work with any new DSMX Rx's you buy. If you fancy a new Tx with voice annunciations etc. and don't need 7 channels, the DX6 looks good, but it won't work your old receivers.

Colin Leighfield29/07/2019 07:11:57
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5962 forum posts
2492 photos

I still use my DX7, had it about 10 years? A long time anyway. No problems so far that I can blame the tx for!

GrumpyGnome30/07/2019 10:31:43
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507 forum posts
145 photos

Another vote to keep it. Mine's about 8 years old and still does all I need.

GG

Peter North 416/10/2019 17:45:13
1 forum posts

I have used my DX7 for nearly 8 years with only one occasion (6 years ago) returning the TX to Horizon (UK) due to an occasional unexplained and temporary glitch.

At that time the RF board was reprogrammed, tested and returned free of charge.

Using the Tx with all my (many) DSM 2 Rxs have been fine until last weekend when on checking the battery state the TX would not switch on. A new battery was obtained but did not correct the problem. Removing the rear TX casing it was clear that the fuse had blown. This appears to be a 3Amp 250v glass item. Temp replacement with a 2.5 Amp item brought the Tx back to life.

Whilst I will obtain and fit the correct size fuse I will initially limit my field testing to one of my converted 'chuck gliders'.

I have examined the charger leads and connections and they all appear to be in good order. The original battery and fitting appears to be sound.

Any comment on the above would be welcome.

Trevor Crook17/10/2019 07:47:51
868 forum posts
65 photos

My son had a similar issue with his DX7 several years ago, but that was triggered by him accidentally using a charge lead with incorrect polarity.

Cuban817/10/2019 09:32:42
2769 forum posts
13 photos

Still use my DX7 that I bought in 2012 - no problems, original battery (checked regularly)  does most things you'd need for the majority of sport aircraft. DSM2 only, but again, it works with all my new DSMX receivers. Have never found the programming difficult - a doddle compared to my old and defunct 35 Meg Futaba FF7 and FF8 that could be a puzzle at times. The Futaba manual TBH just made things worse, it was written so badly. There was even after market books published to help with those radios, so clearly it wasn't just me. BTW, converting the DX7 charging polarity is dead easy, a straightforward wire swap if you can solder. I just bought the TX and RX so no charger or servos - use my Futaba chargers now rather than bin them. I don't know what Spektrum were thinking of by not sticking to a common wiring standard for their charger. Mark the tranny to say the polarity has been swapped if you return it for servicing.

My DX8 G2 is a good radio, I don't think the sticks are quite as nice as my original JR manufactured DX7 and the battery has an in built charger with external power supply plugged in through a horrible little rubber flap which is weird. No lights to indicate charge activity, which is not great but equally not been a problem. I guess the combined battery/charger would be an arm and a leg to replace, a standard battery will be OK though - I see Overlander do a suitable one for twenty quid or so.

David, if the DX7 does what you need for the models that you have at the moment, I'd stick with it unless you simply fancy spending a few quid to treat yourself. The DX8 is full of stuff that I never use, but the extra channel is very useful. Depends if you really need it.

 

Edited By Cuban8 on 17/10/2019 09:35:55

Nigel R17/10/2019 10:20:12
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3109 forum posts
479 photos

OP hasn't been here for a while, but, my take is -

* the G2 / black TXs have two transmit paths, a definite plus

* DSM2 is not a very good protocol, at all. DSMX is a proper frequency hopping spread spectrum effort. I don't know if the original DX7 does DSMX?

As to the channel count, all 8 channels can be quickly used up by a warbird type -

1 left aileron 2 right aileron 3 throttle 4 rudder 5 elevator 6 flaps 7 gear 8 the other elevator, or the other flaps, or gear doors, or ignition cut

" BTW, converting the DX7 charging polarity is dead easy, a straightforward wire swap if you can solder. "

I must admit I'd knock up a converter cable, rather than modifying the TX or charger.

Edited By Nigel R on 17/10/2019 10:21:35

Steve J17/10/2019 10:47:45
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1577 forum posts
47 photos
Posted by Nigel R on 17/10/2019 10:20:12:

DSM2 is not a very good protocol, at all.

DSM2 is fine in a normal club environment. My biggest models are still on DSM2 and will remain so for the foreseeable future.

Steve

Peter Christy17/10/2019 11:10:08
1586 forum posts

Nothing at all wrong with DSM-2. I've still got several models using it, including a large, scale, gasser helicopter. The only real issue with it is that you are limited to 40 DSM-2 transmitters in use at once (!), not really an issue here in the UK!

My personal experience has been that Spektrum quality control seems to have gone downhill in the last few years, and their support for older gear is not good, but there is nothing fundamentally wrong with the system.

I bought one of the original DX-7s when they came out, sold it on when I got a JR DSX-9 (also DSM-2) to replace it, and as far as I am aware, it is still in use today. Certainly my DSX-9 has proven to be just as reliable as any other radio I've owned, and most of my DSM-2 receivers are Spektrum.

All my new builds use FrSky, mainly due to the very good value-for-money receivers, plus excellent reliability, but I'm not planning on replacing any of my DSM-2 stuff anytime soon.

"If it ain't broke, don't fix it!"

--

Pete

Chris Walby17/10/2019 11:20:01
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1004 forum posts
236 photos

What's wrong with DSM2?

Dave flies my Vulcan (flying manhole cover) way further than I ever would and its on DSM2 Rx with satellite, so no problem with range.

I though the only difference was DSM2 didn't dynamically channel hop compared to DSMX.

Please enlighten me, thanks

Cuban817/10/2019 11:24:20
2769 forum posts
13 photos
Posted by Nigel R on 17/10/2019 10:20:12:

OP hasn't been here for a while, but, my take is -

* the G2 / black TXs have two transmit paths, a definite plus

* DSM2 is not a very good protocol, at all. DSMX is a proper frequency hopping spread spectrum effort. I don't know if the original DX7 does DSMX?

As to the channel count, all 8 channels can be quickly used up by a warbird type -

1 left aileron 2 right aileron 3 throttle 4 rudder 5 elevator 6 flaps 7 gear 8 the other elevator, or the other flaps, or gear doors, or ignition cut

" BTW, converting the DX7 charging polarity is dead easy, a straightforward wire swap if you can solder. "

I must admit I'd knock up a converter cable, rather than modifying the TX or charger.

Edited By Nigel R on 17/10/2019 10:21:35

The problem with a converter cable is that it'd be so easy to forget to use it and wind up plugging in the wrong charger. A bit like misfuelling your car, no probs for ages and then a distraction and wham!. If it's possible to do it, then you probably will! crying

The polarity change is not really a 'tranny mod' in the best sense of the term - swapping over two wires on the charge jack in the tranny case is very simple and easy to access.  I also wouldn't get too worried about DSM2, I've never had a problem in a busy club environment or when flying at Old Warden. I do agree that  eight channels are quickly used up on a warbird and sometimes requires a bit of a 'work around' to succeed. Quite a lot of extra money for the extra channel - can't really justify it at present.  Whatever works for the individual as always.

 

Edited By Cuban8 on 17/10/2019 11:33:45

gangster17/10/2019 12:56:28
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965 forum posts
17 photos

As far as the lead polarity is concerned I guess it dates back to the JR convention as that is how they do it. My immediate reaction was there will be a protection diode so reverse connection would not matter. Having thought that though have they removed it as peak detection chargers may not work. As regards this polarity being against convention there was one major amateur radio manufacturer who used both in contemporary radios. With regards DSM2 I see no reason why it’s any less good than any other. I believe people are still thinking with an analogue head on. Ie one model one channel. Now think digital. Your phone line that could not even support mono music can now carry Hf video as well as a number of other internet activities at the same time Check out the Spektrum vids on you tube re mass flying with DSM2

Steve J17/10/2019 13:00:30
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1577 forum posts
47 photos
Posted by Chris Walby on 17/10/2019 11:20:01:

I though the only difference was DSM2 didn't dynamically channel hop compared to DSMX.

DSM2 hops between two 1MHz channels, DSMX hops between 23 (or 27?).

Steve

Nigel R17/10/2019 13:39:21
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3109 forum posts
479 photos

2.4Ghz is pretty susceptible to shadowing and attenuation. The clobber we put in models (an engine, a large lipo) is large enough and solid enough to interfere with the reception of a given frequency quite easily.

DSM2 picks two frequencies at power on. Having these two fixed freqs within the band provides exactly two opportunities to get the signal from TX to RX. Could both be blanked? Yes. Would we notice? Maybe not. You might only be at the right angle or position very briefly. Or you might be flying something slow moving and not notice because you aren't actively moving the sticks.

DSMX hops continuously. It is, as the saying goes, the real deal. The fast hopping provides many, many more chances to get a good signal through within a given time period.

If you're happy with DSM2, crack on. But. The only worse 2.4GHz method I can think of would be to pick one fixed frequency.

It is more difficult to make freq hopping work. I don't think Spektrum did it themselves, in the end it was (I think) Texas who did their chips. So some expensive outsourcing. Trickier physical designs, more complicated software. However, getting out in the market first was the crux of Spektrum's commercial success. It's VHS vs Betamax. DSM2 was the quick hack to put "2.4GHz" on the box. DSMX is the proper job.

Lastly, if DSM2 is so good, why has it been replaced?

Peter Christy17/10/2019 13:41:42
1586 forum posts

Steve J: Also DSM-2 only "Listens Before Transmit" at switch on. Once its found two empty channels, it sticks with them regardless. That's why it failed the EU regulations, which require a "listen before every hop" - not really practical when you are only hopping between two channels. (There are other ways around this by reducing something known as the Media Utilisation Factor - MUF - but lets keep it simple!)

But just because it doesn't meet the latest EU regs, doesn't mean its no good! And if your gear predates January 2015, you can carry on using it quite legally.

Nigel: Its not quite as simple as you make out. Frequency hopping is NOT the same as spread spectrum. It is perfectly possible to make a frequency hopping system that is not spread spectrum. Indeed, you could consider the old fashioned method of crystal swapping as very slow frequency hopping!

Frequency hopping adds an extra layer of resilience on top of spread spectrum, but much of the immunity comes simply from the spreading process, regardless of frequency hopping.

--

Pete

 

Edited By Peter Christy on 17/10/2019 13:46:38

Steve J17/10/2019 13:52:43
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1577 forum posts
47 photos
Posted by Nigel R on 17/10/2019 13:39:21:

Lastly, if DSM2 is so good, why has it been replaced?

Because it isn't compliant with EN 300 328 1.8.1 (and is a bit dodgy with regard to 1.7.1).

I don't disagree that DSMX is better, but I have no problems with DSM2 and I have a lot of telemetry data to back that up.

Steve

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