This is now my third 2.4 GHz radio after first having used a special module on the Futaba 3VCS, and then a Spektrum DX6 with the Noux (now sold). It's the cheapest model, a DX5E, which will be used with my newest boat (soon to be featured on this site...).

It seems the Spektrum engineers are not reading this blog too keenly, I suggested an internal antenna back in 2007. Even if the antenna is short I don't like it sticking out of the transmitter, so the first thing to do with the brand-new radio is to open it!

Here's how the transmitter looks opened. Note the small battery compartment which only takes 4 AA-cells (down from 8 in the early days and 6 on the older DX6). There's plenty of room for the antenna at the top of the transmitter, but just outside the top edge there's a metal carrying handle which I thought wasn't the best thing to have close to the antenna. So off it goes:

The handle detaches by opening two nuts on the inside of the case, after cutting a way some hot-glue which was used to secure the nuts.

Then the antenna needs to be made a bit smaller. What sticks out of the transmitter is actually first an empty plastic tube which just extends the antenna itself a little further from the case. By cutting away the small plastic bits that prevents the antenna from rotating 360-degrees it all disassambles nicely, and I'm left with the narrow coax-cable and the antenna:

The antenna can now be hot-glued to the top of the back casing:

I've also applied some hot-glue to the holes where the handle was attached. Now all that remains is to close the case again, making sure that no wires are caught between the casing or screws:

And we have ourselves a Tx with an internal antenna! The way it should have been designed in the first place - if you ask me. What remains is to tape or plug the old antenna opening. Previously I've had no range or other problems whatsoever with this kind of arrangement, but naturally I take no responsibility if you try this and void your warranty and damage your transmitter.

By popular demand, some notes on how I've placed the antenna of my Spektrum DX6 transmitter inside the case. I've been using the radio like this ever since I got it and provided that you hold up the radio more or less vertically and not hide behind large metal constructions or things like that the range is fine. The benefit of the internal antenna is that I don't have to worry about breaking it while sailing it or storing the protruding thing in the toolbox. When it rains it's nice to fit the whole transmitter into the rain-cover which doesn't have any (potentially leaking) holes (other than the two holes for my hands!). A plug for the antenna hole to prevent dirt etc. entering the Tx would probably be a good idea.

If someone has a feeling for what theoretically a 2-3 mm wall of plastic does to an RF signal at 2.4 GHz, let me know.

Here is the back cover and six screws that hold it removed along with the battery (I've put Deans connectors on the Tx battery to simplify charging). With a stock DX6 the antenna would be sticking out at the top and there would be a few extra pieces of black plastic supporting it. I remember I broke some of those black plastic parts when I disassembled the antenna - so proceed carefully if you think you want to go back to the stock configuration sometime. I didn't touch the electrical connection of the antenna at all, the thin grey coax that comes out of the antenna attaches to the RF PCB just like it does on the stock Tx.

Here's a close-up of the antenna. You can see a part of the old antenna-hinge around the grey coax to the left (a bit dangerous to cut it away with a knife or pliers since you risk damage to the delicate coax). I've taped the antenna upside down to the RF board. There are probably other places inside the case the antenna could fit as well, but this seems to work OK.

If anyone has done something similar do let me know! I'd be happy to post pictures here if you send them to me.

Spektrum: I hope you are taking notes, I expect your next radio to have an internal antenna!

Talking about DX6 modifications, I did order the voltage regulator for the improved runtime modification, but the runtime with 2700 mAh NiMH's is just fine so I haven't installed the improved regulator yet.

Update 2007Nov17:

Olle Martonen sent me this pic of his modified Spektrum DX7. He mounted the antenna horizontally behind the regulator/switch PCB. Also note the wooden plug in the antenna hole. Not much sailing done with this system yet, but range-checking on the ground indicates there should be no problems.

I also got some observations be email on RF issues from a mobile-phone perspective: A few mm of plastic will not attenuate the signal measurably. Conducting materials are worse, like some mobile phone shells that are covered with carbon-containing paint, or your fingers on the back side of the transmitter. My placement of the antenna close to the RF-box (the metal square), and the PCB (also metal-coated), is not optimal, and could lead to an attenuation of 3-5 dB. A distance of 2-3 cm to the conductive parts would be better, so I'll maybe look for other places inside the Tx where the antenna could fit (Olle's example above is a bit better since the antenna is farther away from the RF-box).

Update 2007Nov22:

Winston Mathews sent me this picture along with a description: "Here are our modified DX6 radios. 2200 mAh batteries, new voltage regulator, jib-trim potentiometer and now "internal" antennae (mounted horizontally). Range is unaffected. Thanks for the idea and your help. I would advise to install the voltage regulator. We can sail for two days without recharging. " Photo by Jack Wubble, owner of the open radio in the pic. Discussion on this is over at the EC12 discussion forum.

Update 2007 Nov 23:

Some text and images on modifying a Futaba 2.4 GHz radio on the EC12 website.

Spektrum recently introduced an updated version of the DX6: the DX6i. Horizon Hobby also has an article on the new radio.

This one uses 'DSM2' technology which is described as giving 'full range'. Not sure what that means, but range should be better than with the first generation of 2.4 GHz radios, which at times was problematic (if you did something specific that cut down on the range).

I think the original DX6 was more or less a carbon copy of an existing JR transmitter, but the DX6i seems to be a new ergonomic design. Instead of buttons for navigating the menu it has a roller-device, and there's a new bigger LCD for programming.

The antenna still sticks out at the top even though nobody has had a mobile phone with an external antenna in years. I've mounted the antenna on my own DX6 inside the plastic case and it seems to work fine. I predict and hope that the next version in 1-2 years from spektrum will have the antenna mounted inside the Tx (no fear of breaking it, no problems with leaking rain-covers).

It's going to be in stores in December, for around $180 without servos, which is similar to what the 6-channel 2.4 GHz Futaba sells for.

HiTec has replaced their previous robot servo (HSR-5995, now discontinued) with a new version called HSR-5990. The specifications are roughly the same as for the old model: torque is 24.0 or 30.0 kg.cm depending on if you use a 6 V or 7.4 V battery, but speed is down a bit from 0.15s/60deg to 0.17s/60deg (6 V). The gears are Titanium alloy, and as is visible from the picture the new servo adds a heat-sink to the casing.

Maybe this is the winch for my next boat? At a cost around $110, weight of 68 grams, and 'ludicrous speed', it looks like a strong alternative to a drum-winch. Anyone have good or bad experiences with the 5995 or the new 5990?

Spektrum has come out with a new 7-channel system called the DX7. It's not on their website yet, but Horizon hobby has it for sale. This one is supposed to be a radio for 'real' models, not only meant for park-flyers like the DX6. I wonder if there will be a problem with 'CE' approval with regards to the output power - A rumor I heard was that the 'CE' marked version of the DX6 has a reduced output power compared to the US model ??

There's also a new player on the market, Xtreme Power Systems, which will introduce their new xtremelink module+rx combo shortly. They too promise increased range and reliability. In contrast to Spektrum, who talk about either 40 or 80 simultaneous working modules, Xtremelink claims up to 390 000 simultaneous active modules ! Also, up to 1 mile ground based range. Pricing and deliverytime still open.

The Futaba modules I noticed back in January were on display at Model Expo in the spring but the local agent said it would take some time before they come to market. I've detected no activity in the Futaba camp so far...

For the new boat, I've bought myself a DX6. Naturally I'm going to mod it a bit before use . I've ordered a switched-mode regulator which supposedly will reduce the current drain of the Tx a lot. Also, I've gotten very used to the 'no antenna' look and feel of the Futaba 3VCS with a Spektrum module (especially usefull when it rains, the whole radio goes inside the Tx-cover, no leaking hole for antenna needed). But the stock DX6 has an antenna that sticks out . Cell-phones have had internal antennas for years and nobody buys phones with external antennas anymore - so the DX6 antenna needs to go inside the case too ! I'll report later how that goes...

"The good thing about standards is that there are so many to choose from"
-- Unkown
There a number of connectors that are called SMA, but nevertheless are different and uncompatible. Either the plug or socket can have the pin end of the connector, and some narrowminded device producers have chosen a standard with reverse threads on the connectors. So be sure to check for compatibility when buying SMA connectors...

This is the coax cable that takes the signal from the RC-pot to the aft deck. The deck connector is a wall-mount type. There are a number of grades of coaxial cable. Choose one that is narrow and has a reasonable attenuation at 2.4 GHz. If I remember correctly this cable is called RG-316 with an outer diameter of 2.3 mm. It has slightly less attenuation than the "normal" narrow coax, RG-174, found in most places.

Here is the deck connector mounted far enough back so there is plenty of room for the no1 boom to swing by. This picture shows the 2 dBi omnidirectional antenna that I have used most during the season.
Look long enough at this picture and you will be hypnotized by the deck pattern to think only positive thoughts about Texalium !

Since the 2.4 GHz ISM band is used by lots and lots of other equipment there are plenty of different antennas available. From left to right: 5dBi omni, 2 dBi omni, and 0 dBi omni. The 2 dBi which I have been using (in the middle) is about 95 mm long - to give you a sense of scale. The 5 dBi is a little big and heavy to use on the boat but Rob Guyatt has used one on the Tx module - he says it improves the range a bit but not very much.

First I bought some antennas and cable from Wimo in Germany but then I also found a Finnish company, Elcard (www.elcard.fi), selling this kind of stuff.

During the season I have been fairly happy with this arrangement. If I remember to keep the Tx antenna vertical and not stand behind very many people or large metal objects then the range is good. The precision and jitter etc. properties are as good as PCM. The modification described here is a little hard to do so I think I will go for something simpler next time. Rob Guyatt has used just a piece of coaxial cable to extend the stock antenna well above deck. Everything soldered together but threaded above deck through a tube allowing replacement if neccessary.

The Rx draws a little more current than a PCM receiver does but I have not noticed a difference. The Tx module draws less current than the 27-40MHz modules do and I consistently get around 7 hours of uptime on the Futaba 3VCS using an 8-pack of about three year old 1600 mAh NiMHs.

Interestingly, I note that spektrum has quite recently released a complete 2-stick system, the DX 6,using this technology. It's labeled as a park-flyer system and sells for a reasonable 199 usd. How long before anyone tries this on an IOM ??