Integrating Bluetooth with an Amateur Radio Transceiver

Robert Stampfli / KD8WK — May 2011

These notes describe the steps I went through to interface a Bluetooth adapter to my ham radio transceivers in order to use a wireless Bluetooth headset with the rigs.

I enjoy rag-chewing. Indeed, my preferred way of operating on HF is to use a VOX-controlled headset with boom mike. When I acquired a FT-897 transceiver, one of the first things I did was to purchase a Labtec LVA-8420 headset and adapter from W2ENY. This setup served me well – I consistently got excellent audio reports – but I was still tethered to the rig and so could not move around my hamshack, and the cord, which was rather stiff, kept getting in my way. One day, while surfing the net, I came across this nifty article by Frank Dziurda/K7SFN which piqued my curiosity. I decided it was worth the investment to give Bluetooth a try.

Obtaining the hardware

Unfortunately, it soon became obvious that I might be a bit late to this party: Although the Blue Parrott B-250 headset Frank recommends is still available, I found out the Jabra A-210 Bluetooth adapter is no longer being manufactured. Apparently, most cell phones today now come with Bluetooth built in, and there is no longer a market for Bluetooth adapters. I could not find a store anywhere, bricks-and-mortar or online, that carried the Jabra A-210. No problem, I thought; they are still available from the reseller market on Ebay.

The Jabra A-210 is a neat little widget about the size of a large postage stamp and maybe 1/4" thick. It was intended to plug into the headphone jack of a cell phone and provide Bluetooth capabilities for phones that do not come with it. It comes with it's own internal Li-ion battery which provides up to 8 hours of talk time, or unlimited talk time if left on the charger. It has a 3/32" audio plug (the standard for mating a wired headset with a phone), a socket for plugging in its charger, a push button for turning the device on and off, a 3-way switch for selecting the proper audio level to the cell phone, and a recessed button to initiate headset pairing. Because the prices for the increasingly-rare new A-210s were getting pretty hefty, I ordered one from someone selling theirs used.

The Blue Parrott headset was easier to acquire, if a bit pricey: It is a highly regarded headset most cell phone power users seem to like. Its claim to fame is its exceptional noise-cancelling capabilities. It is touted as providing a whopping 16 hours of talk time on a single charge, and has three buttons that perform a variety of functions. I ordered one of these from Amazon.

Problem 1: The Jabra's unfortunate battery design flaw

Jabra A210 Internals
The Jabra A-210 with its top off

When these two items arrived, I found the Jabra wouldn't charge. The red charge LED would light briefly and then extinguish. I returned it to the seller for a refund and ordered a "new in the box" A-210 from a different Ebay seller. Amazingly, this one exhibited the same problem as the first, so I did a bit of Googling and found this site.

It seems the A-210 has a latent design glitch: Li-ion cells can behave in impressive and undesirable ways if overcharged, so Li-ion batteries all come with some electronics designed to discourage a pyrotechnic display. In the Jabra, this amounts to a very small daughterboard affixed to the top of the battery. However, it seems this circuit does more than just prevent overcharging an already charged battery; it also seems to prevent charging a battery whose voltage is too low. This was not a problem when these adapters were new and flying off the shelves. Unfortunately, any A-210 adapter sold today is at least two years old, and even those "new in the box" units are probably at a point where the battery has self-discharged enough to make the charging circuit balk.

Jumpstarting the Jabra A210 Battery
Jumpstarting the Li-Ion Battery

I decided to bite the bullet and pry open the case to see what could be done. With a small screwdriver, I managed to separate the case and gain access to the interior. This is not to difficult a task, but I broke several of the internal plastic catches/standoffs while doing so. I'm convinced that this is nearly unavoidable, but fortunately it does not affect the operation of the unit. Also, the case material is such that a bit of electrical tape adheres well and does a fine job of holding the unit together again once the time comes to reassemble it. Just be careful not to lose the small light-colored plastic button that fits over the on/off switch, something which is easy to do.

Following the advice from the site, I attached a small cheater cord (with component clips on each end) from the negative terminal of the battery directly to a ground point on the A-210's motherboard, permitting the battery to charge. I found I did not have to cut the orange tape to do this; With some work, I could attach one end of the clip to the negative battery terminal, and the other to a spot on the ground backplane on the bottom side of the board just below the Bluetooth antenna. After about 15 minutes I could remove this strap and the unit continued to charge with the daughterboard in-line.

Depending on the level of discharge, the Li-ion cell may exhibit unsafe behaviors and I would suggest watching the cell closely during the remainder of its first charge cycle. While I have never witnessed this personally, if the cell becomes hot, cease charging it immediately. What I have observed is that the airtight Mylar sac enclosing the battery can become bloated from what appears to be outgassing components that are a byproduct of the charging process. If the internal pressure becomes excessive, stop charging and let the cell sit overnight. Usually this allows the pressure to fall and the charging can be recommenced the next day. The charge light should automatically extinguish after two or three hours, once the cell achieves a full charge.

Wiring the Jabra to the FT-897

Connecting Adapter to the FT-897
Connected & Ready to Go!

Next, I fabricated the wiring harness for the Jabra. Since I didn't have a spare RJ45 stub, but did have the RJ45-to-stereo-jack adapter that came with my wired headset, I decided to interface my Jabra to this. However, I see no reason why you can't build a harness directly around an RJ45 plug, and I would simply have cut the end off an Ethernet cable and used that if I had chosen this route.

The Mic Connector Pinouts
The Mic Connector Pinouts
(as seen from front of rig)

The Jabra has a 3/32" "stereo" plug designed to connect to a cell phone. Thus, you'll need a 3/32" "stereo" jack to mate with it. However, we aren't dealing with a stereo signal here. The Tip on the Jabra plug is the Bluetooth Audio Out, and must eventually find its way to the Mic connection (pin 5) of the RJ45 jack on the FT-897. The Ring (middle) connection should be connected to the Tip of a 1/4" headphone plug that will go to the headphone jack on the rig. The Sleeve on the Jabra's plug is ground, and should connect to both the sleeve of the 1/4" headphone plug and the Mic Gnd pin (pin 4) of the RJ45 connector. It doesn't matter whether you use a stereo or monaural 1/4" plug. The FT-897 is forgiving in this respect. I used a stereo plug and left its ring unconnected. For this project, I found everything I needed in the junk pile, although I'm sure Radio Shack could provide all the necessary connectors. For RFI immunity I used RG174 spaghetti coax from the 3/32" jack to the 1/4" plug, and to the Mic input, and found that 4-5" was about the right length in each case.

Works fine with other Ham Transceivers, too

Although I originally devised the above interface to work with my FT-897, it works just as well with my old Kenwood TS-430S. Of course, the Kenwood's microphone connector is different, but any adapter that allows the rig to work with a corded headphone-with-microphone headset should be capable of interfacing with the Jabra.

Pairing the Bluetooth devices

Once the Jabra hardware is properly interfaced to the rig, the next step is to pair the headset with the adapter. The instructions are pretty straightforward. Basically, the procedure involves turning on the Jabra by holding the white button in until the blue light starts flashing, then putting the headset in pairing mode by holding its MFB button down for 15 seconds, then pushing the recessed "pairing" button on the Jabra until the blue light comes on solid, and waiting. Sometimes it takes a couple tries. If you have a different headset, follow the procedure that comes with it.

Once paired, verify that the receive side of the headset is functional: Set the audio gain on the transceiver to about the 8 or 9 o'clock position. Plug the 1/4" plug in the headset jack. Verify the Jabra and headset are both turned on, and click the MFB button on the headset. In essence, you are telling the headset you want to make a phone call. In a few seconds you should hear the transceiver's audio in the earpiece. If not, try adjusting the AF Gain. However, I find my setup provides plenty of audio. In fact, I prefer keeping my headset adjusted to its minimum audio setting and then adjusting the AF Gain control on the transceiver to what's comfortable.

Operating with a Bluetooth headset

The Jabra adapter has a three position recessed switch which basically provides a coarse control of the audio level to the Mic input. I've found position 3, which has the most audio, works best with my rigs, but perhaps position 2 might be more appropriate for some transceivers. On my FT-897, I get the best audio reports when I set the SSB Mic Gain (Menu 81) to around 15-20 and I leave the VOX Gain (Menu 88) set to max (100). (The noise cancelling feature of the Blue Parrott B-250 really does seem to work – there are few legitimate false triggers, even at maximum VOX gain, but see below.) Set VOX Delay (Menu 87) to suit your taste. You also may want to fiddle with the Beep Vol (Menu 14) and CW Side Tone (Menu 29).

The audio reports I have received using the Blue Parrott B-250 and Jabra A-210 have been uniformly good; not quite as good as the wired Labtec, but better than the hand-held mic. I have yet to encounter a mode or band where the Bluetooth adapter or headset have exhibited any symptoms of RF interference or feedback, even when operating at near the legal limit. On the other hand, the wired Labtec headset proved to be susceptible to RFI on certain bands, particularly 2 meters.

One regret is that the usable Bluetooth range is less than I would prefer. Although the Jabra adapter and Blue Parrott headset claim a usable distance of "up to" 30 and 60 feet respectively, I find these numbers optimistic. Maybe they are attainable in free space. I can more-or-less move around the hamshack with impunity, and even this is clearly superior to being tethered to the rig via a 6-foot cord. However, once I am no longer within line-of-sight of the Jabra, things gets noisy fast. I can walk from my shack down the hall, down the stairs, and into the kitchen without losing the connection, but at times it becomes quite noisy to the point of occasionally being uncopyable. If I transmit while out of the shack, I'm likely to elicit some comment about my audio breaking up. Apparently, Bluetooth digitizes the audio and sends it out as a stream of packets. The audible effect is as one might expect if an increasing number of these packets are received with errors and replaced by small quanta of silence.

If I continue to roam even farther from the ham shack, such as out into the yard, the Bluetooth connection eventually drops, and once broken, it requires a return to the shack, i.e., to line-of-sight connectivity, to re-establish the link.

Problem 2: The Jabra's Battery Saver Circuit

Defeating the Jabra auto-timeout
Defeating the Jabra's Auto-Timeout
(click image to enlarge)

After using the Jabra in a ham environment for a while, another insidious problem becomes apparent, especially in long-winded roundtable QSOs. The Jabra has a built-in battery saver "feature" that allows it to conserve power by placing itself in a power-save mode when it judges that nothing is going on. It does this by detecting a minute of silence from the transceiver (which it believes to be a cell phone). But, since (unlike a cell phone) ham radio communications are half-duplex, the mechanism the Jabra uses to detect lack of use – silence from the transceiver – occurs every time there is a prolonged transmission. The net result is that after sixty seconds of transmitting, the Jabra puts itself to sleep and silently drops me off the air until I unkey, realize I have no audio, and manually re-enable the headset by hitting its multi-function button. If I have the transmitter manually keyed (manual PTT) at the time, this condition is difficult to discern in real time – its behavior is analogous to timing out a repeater. If I am on VOX, the transceiver drops back into receive at this point (but the audio remains muted while in power-save mode). This gives some small indications of a problem, if you are attentive, but still results in an embarrassing and not easily resolved over-the-air glitch. Perhaps if my rigs had a TX Monitor function, this could be employed as a workaround, but alas, they don't.

Fortunately, VE3LC and VE2ZAZ have figured out a fix for this problem. It involves adding a 47K resistor between pin 1 of the timer chip, located on the underside of the Jabra's circuit-board, and ground. This fix has the desired effect, but is quite challenging to install on the Jabra's surface-mount circuit-board populated with super-small components. Here, a picture is really worth a thousand words. VE2ZAZ has captured two ways of performing this mod, here and here. I elected to try yet another approach: I used a 1/8 watt conventional carbon film resistor, which is a perfect size for connecting between the component and one of the test points located on the circuit-board's ground plane just to the right of the mounting-bracket hole. Be very careful: It is quite easy to create a solder bridge where it doesn't belong or dislodge a microscopic component!

The One-Week Report

Bluetooth is addictive. Maintaining the adapter and headset – keeping them charged and ready for use – takes a certain amount of time and diligence, but it's amazing how free it feels to not be physically tethered to your rig, even while sitting in front of it. As I am typing this, I'm also engaged in a roundtable with some friends on 160m. A few minutes ago, I took the opportunity to walk down to the laundry room, unload the dryer, take the clothes up to my bedroom, and put them away. The Bluetooth channel got noisy once I left the shack, but for the most part the QSO remained copyable throughout the task. While I would prefer that this Bluetooth setup allow me a greater range of solid copy, I nevertheless believe it is destined to become an indispensable part of my ham-related bag of tools, if it hasn't already.

The Six-Month Report

To be frank, after six months of use, Bluetooth has not integrated as seamlessly into my ham radio operations as I had originally hoped it would. For the most part it works acceptably well, but there are several little glitchy problems, aside from the lack-of-range issues, which continue to plague me in everyday use:

Even when situated adjacent to the Jabra Bluetooth adapter, it seems the headset occasionally gets corrrupted packets. This manifests itself as a "thump" in the earpiece. While an occasional thump is not terribly disconcerting, their numbers do rise occasionally to a level where they can be annoying.

In the same vein, I have observed instances where the VOX occasionally and semi-randomly false-triggers for no apparent reason, when neither significant local or receiver audio are present. I suspect this may be the opposite side of the above problem – Bluetooth data packets becoming lost or decoded incorrectly, this time in the Jabra adapter, and showing up as a pop or thump at the rig's mic input. I don't have a second Bluetooth headset that I can test with, so I can't say whether this is a flaw in my particular Blue Parrott headset or a design flaw in either it or the Jabra. I do have several Jabra adapters and it has been observed with each of them to varying degrees. Again, it is tolerable for casual use, but occasionally becomes annoying.

Finally, it appears that somewhere either within the Jabra unit or the headset, a portion of the receiver audio signal is being fed back to the microphone input, and if the audio level on the rig is set high enough, it will occasionally false-trigger the VOX in response to the received voice peaks. Fortunately, it takes a fair amount of audio to provoke this, and the rig's anti-VOX can also be used to compensate for the effect.

I suspect some of these issues are not Bluetooth issues, but rather problems that arise from using a device designed for use with a cell phone in a ham radio environment. The upshot is that I've had to be a bit selective as to when I use my Bluetooth headset. In the right set of circumstances it works surprisingly well, but in some environments it has proven itself not up to the task.

Some Final Musings

After publishing this white paper, a couple people have pointed out to me that other Bluetooth adapters exist. In particular, Cardo makes several models, including the BTA II, which appears to be quite similar to the Jabra A-210. Unfortunately, this unit also appears to be out of production, and like the Jabra, in short supply. Additionally, Motorola also produced a model DC600 Bluetooth adapter for their cell phone line. This one is unique in that it has no internal battery, but is powered from the cell phone. However, while it might be possible to adapt it for ham radio purposes, I suspect the DC600's Moto-specific design would pose significant retrofit problems. In addition, the Jabra instructions indicate that the Motorola Mic input requires a relatively low audio signal level, which this unit would logicially provide. It may be possible to adjust the Mic Gain on the FT-897 to accomodate the lower signal level, but I have not tried it.

In an email exchange, Frank Dziurda/K7SFN, mentions that several of his ham buddies have graduated to using the Plantronics CS-351N and CS-361N headsets, which are based on the DECT wireless standard instead of Bluetooth, and which consequently have a much greater range.

I have no experience with any of these units, and so cannot comment on or recommend them. If you use one, especially if you have integrated it with your ham rig, I'd be interested in hearing from you.

Web Resources

I hope this white paper has proved helpful to you, especially if you decide to implement your own Bluetooth interface. If you have any questions, please feel free to drop me a line. I'm good in QRZ, and I'll be glad to try to help you out.

73 & happy Bluetoothing, de kd8wk