VOX Problem with Autocom + TK-3101

[FlyingFinn]

I know this should work but it doesn't....

 

I'm in the process of putting together two Autocom setups, both with Super Pro-AVI and Kenwood TK-3101. The Kenwood radios are connected to autocom using Part 102, which provides also the power to the radio via the autocom.

 

With the radios "bike powered" like that, the Autocom VOX (to transmit on the radio) works like crap. VOX is very choppy and in general is pretty darn useless.

 

I have an extension cable to move the radio few feet away from the Autocom. That seems to help a little.

Also, if the radios run from their own battery (only mic and speaker are connected back to the Autocom) then VOX transmit works fine.

 

To me it seems the Autocom gets messed up by the RF transmitted by the radio.

 

But this setup is supposed to darn work! I've seen some of you guys with Autocom and a TK3101 stuffed into a tankbag and it works. What's the trick?

 

I have two of everything here plus some spares. All combinations of TK3101/Autocom/cables do the same so it doesn't appear to be an issue with some faulty component.

 

What does it take to make this work?

 

--

Mikko

[johnlt]

Mikko, that's the setup I use and have used for several years with no problem. I normally like to use a PTT but can also put the PTT in "vox mode" and the vox works fine. Have you tried it with PTT?

john

[FlyingFinn]

Hi John,

 

That's what I thought, I remember you had pretty much exact same setup.

 

With PTT it works. The problem really is the VOX.

There's no noise or anything like that, just that when the Kenwood is within couple feet of the Autocom, and is "bike powered" the VOX pretty much quits working.

 

John, do you use the Part 102 to power the radios, or the other Autocom part for Kenwood that is more like a battery pack with a cable?

The Part 102 is just a wiring loom that connects to the Mic and Speaker jacks and also straight to the battery contacts of the Kenwood.

 

Part 102

 

 

What irritates me a little is that I'm now using 100% Autocom parts. Every cable is from them.

When I cobbled my own cables for the old Pro-M1 + Yaesu radio it worked fine....

[FlyingFinn]

Here's another fellow on AdvRider that describes the same issue I have. Unfortunately no fix was ever provided in that thread.

 

Autocom + Freetalk XL + VOX = Interference?

 

--

Mikko

[johnlt]

I use the autocom part that is like a faux battery pack. Very nice setup and work on vox nicely. I normally keep my radio in the tankbag on the GSA and under and in back of the rear seat on the RT. The range is so poor anyway with the rubber ducky antenna that the orientation of the antenna didn't seem to make any difference.

[Penforhire]

Try something that worked for me and my buddies, though it may have zero effect on your issue. Set the volume control on the Kenwood to half or less. There is something really odd that happens to our VOX control at higher settings.

 

We all keep our radios and Auto-c's (Pro 7's) in the tank bag.

 

None of us uses bike power through the Auto-c to the radios though. One uses the OEM NiCd. One uses an fake battery-to-cig lighter adapter (E-bay, from China). My fake adapter broke so I use an aftermarket high-capacity battery bought on E-bay. Works great for me. The 600 mAH OEM NiCd was too small for me.

[FlyingFinn]

I'm starting to think the Part 102 doesn't really work that well with Pro-AVI + TK3101.

Maybe there's some additional filtering inside that faux battery pack that makes it all work.

 

Tonight I'll experiment with different home-made power cables for the radio.

Using the Part 102, there's no way the VOX would work at all if the radio is mounted right next to the Autocom

 

Thanks for all the suggestions and keep it coming.

 

--

Mikko

[KDeline]

Set the volume control on the Kenwood to half or less. There is something really odd that happens to our VOX control at higher settings.

 

 

He is right on that, I receive chopped transmissions at very high volume, but this also will happen with PTT at high volume. OTOH I have had so many issue's with VOX not working as advertised, we just use PTT now all the time.

[allikanbe]

I have a bike powered Kenwood in my tankbag and an autocom under my seat. My friend has a AA battery powered Kenwood in his tankbag with his autocom in the tankbag. We both use PTT buttons and there is no interference. We have never noticed any interference.

 

by the way, Is there a battery eliminator for the Kenwood XLS radio?

[FlyingFinn]

I'm not aware of a battery eliminator for the XLS.

 

You and your friend both have setups that work on my bench too.

Either,

a) Good distance of physical separation between Autocom and the bike powered radio, or

b) battery powering the radio.

 

That works for me too.

A bike powered TK3101 in close proximity to the Autocom and VOX getes reeeely choppy.

 

--

Mikko

[FlyingFinn]

It's RF feedback into the Autocom that causes the problem.

 

I put an RF attenuator pad right at the Kenwood antenna connector, that cuts down the radiated RF power but current draw will be still the same.

 

- With 30dB pad at the Kenwood antenna the VOX works as intended (duh!)

- With a 6dB pad it's much better, radio has to be quite close to Autocom to cause problems.

 

I only found one of those split ferrite chokes from my junk drawer but placing that over the radio lead does also help. Not quite as much the 6dB pad but it does help.

 

So with more time I'm going to try:

1. Program the TK3101 to low power setting ( think they are programmable to TX either 2W or 0.5W) ((drop from 2W to 0.5W is incidentally 6dB))

2. Install RF chokes on all cables entering the Autocom

3. Solder some RF bypass caps on the radio end of the Kenwood cable

4. If problems still persist, add more RF bypassing on the headset leads inside the Autocom.

[Tom B]

The Kenwood radio has a low battery cut off system. It is possible that in transmit mode the radio is drawing too much current from the Pro and the 9 volt output from the Pro is being pulled down too much when you transmit. If the radio detects the power supply is too low it will consider this a low battery voltage and stop transmitting to help protect the battery, often with a bleep from the radio to tell you that the power is low.

 

If the system works well with a fully charged battery fitted to the Kenwood, and even works well for receive when bike powered via the Pro, but suffers unreliable transmit when bike powered via the Pro then to test PLEASE TRY THIS; Use one radio as a battery powered hand held radio to transmit; connect the other radio to your Autocom and set the Kenwood volume below half. Use the battery powered portable Kenwood to transmit to the radio that’s connected to your Pro and you should find that it is receiving reliably through the Pro system. Now if you stop transmitting on the portable radio and speak via the Pro microphone and activate the Pro VOX your speech should be received on the portable hand-held Kenwood (check volume is set about half).

 

The US version of the TK radio seems to draw more current when in transmit mode than the UK & EU versions. This is why I redesigned the 2009 Pro AUTOMATIC to have 12 volts output for the transceiver lead and the new version of the Kenwood radio bike powered interface lead has a new digital switched mode power supply built into the back of the dummy battery pack to help overcome such issues. The early Pro systems have 9 volts output rated at 1 amp peak, and normally 750mA. The NEW 2009 Pro Automatic has 12 volts output rated at 2 amps and the new switched mode power supply built into the radio interface lead is rated at 3 amps, so the chances of volt drop when transmitting are considerably reduced.

 

TRY fitting a 1000uF (or higher) 16volt capacitor across the back of the radio power contacts (MAKE SURE YOU GET THE POLARITY CORRECT!) if this does not work let me know.

 

VOX BOUNCE

Obviously when I designed the Pro system I had to allow for various two-way radios to be used and some have very low audio outputs compared to some that have very high outputs in comparison. The Kenwood has very high/loud audio output and so care must be used not to set the Kenwood volume too high. If you consider the overall lengths of the combined headset leads, plus coiled headset extension leads, the are fairly long, and if the volume is set VERY LOUD because you have FOUR speaker wires running alongside the microphone wire, in both headset leads, you can get BLEED from the speaker wires across to the microphone wire/s, and if this bleed is high enough then the VOX can sense enough signal on the microphone wire (leaking across from the speaker wires) that it thinks you are speaking and so activate the VOX. The simple fact is that for this to happen we are talking about VERY HIGH volume levels that are normally far louder than is required and the SOLUTION is to turn the Kenwood volume control to a low to medium setting. The main reason why someone may feel the need to turn a Kenwood radio volume so high as to cause VOX bounce is normally because they are over compensating with excessive radio volume because their speakers are poorly positioned, or they are using excessive attenuation earplugs. Following the INSTRUCTIONS, if you held/positioned the speakers PROPERLY/DIRECTLTY over your ears and tested the system, you would find plenty of volume (enough for 185mph) with the Kenwood radio volume set below or to about half.

 

RF interference

Two way radios can and should transmit a clean radio signal, however it is possible for them to transmit plenty of interference if the antenna is damaged or out of tune, which unfortunately can be a common problem with rubber duck type antennas.

 

As I said above, the US version of the Kenwood TK seems to draw more current when in transmit mode than the UK version which suggests that it is perhaps transmitting a higher output level, and if this higher transmit power also has harmonics/interference caused by an out of tune antenna then this could cause radio interference (RF) issue to other electrical devices such as your Autocom or even perhaps to other electronic devices such as ABS and engine management computers. SOLUTION; if you can set the radio output level to a lower setting and/or move the radio away from other electrical devices, taking into consideration that the radio will have a better transmit range if the antenna is held vertical and as high as possible.

 

So to summarise; if the radio/Pro system works well in transmit mode with the radio close to the Pro system then the radio is not transmitting loads of interference at a high level.

 

If your installation cannot be changed then try screening the Pro with a metal shield that is well earthed to the bike, and if necessary also try shielding the Pro cables in close proximity.

 

Perhaps you can fit a remote antenna away from other electrical devices and mount it vertical and higher up for improved range?

 

If the radio is mounted under the seat then it is very important to keep the antenna well away from the bike frame/earth otherwise most of the transmit signal will be sunk to earth and you will considerably reduce transmit range. Also try to stop the antenna wiping/bouncing as this can cause flutter/distortion. On my bike I have the Kenwood laying horizontal away from the bike frame and the antenna is exiting the back of the bike (via a small hole) so that it is clear from the bike frame and does not bounce/flutter.

 

Hope this helps

 

By the way, although I was the original designer/owner of Autocom, I am retired from that position now so cannot continue to provide the level of support that I used to; the new owners should oblige that for you! However when I see something of personal interest or that may otherwise be technically challenging then I may offer my experience/help.

 

Tom

 

[Tom B]

Additional note;

 

If you use an independent power supply (11 to 18 volts input reduced to 9 volts clean DC, rated at say 1.5amps or more) then this could be used to power the Kenwood.

 

You could use a part 2342 but would need to open up your Pro system and disconnect the 9 volt lead from the white 9 pin connector on the transceiver lead and connect this to 12 volts within the Pro, being an easy mod if you know what you are doing

 

[Ken H.]

Tom, how nice to ‘see’ you here again! I suspect you can’t tell us THE story, but never-the-less your input and guidance is always recognized and appreciated!

 

[/hijack]

 

[SteveW]

 

+1 on Ken's comment. I'm very pleased to "see" you again...

 

You've helped me out on many occasions - sometimes directly and more often via replies to other inquiries.

 

My old Autocom / Kenwwod setup continues to work flawlessly except to the occasional user error

 

GOOD LUCK with whatever your new ventures become.

 

 

[FlyingFinn]

Tom, I really appreciate your response, big thank you for still providing your invaluable support for the Autocom user community.

 

Going back to my specific issue.

My VOX problem is not the VOX bounce as you describe it. I'm doing all my testing on my work bench in a quiet room and all volume levels are very low. Also my headset is properly installed in the helmet (works fine for rider - passenger coms at >80MPH).

 

My issue is not either the low battery warning on the Kenwood. I've seen that and know how that "looks like". Additionally, I can re-create my issue even with a battery powered Kenwood radio if I place it very close to the "Pro".

 

I'm quite sure I'm suffering from RFI problem. Radiated RF energy from the Kenwood gets coupled to the circuitry of the "Pro".

The symptom of that is a huge change in VOX sensitivity. The RFI makes is appear as if the BGNS would be picking up a tremendous noise level. Sitting at my desk with helmet on, I have YELL into the microphone to activate the VOX when this RFI problem is present. With radio either placed far away, or attenuated with an RF pad, the VOX works normally.

 

Here's my biggest clue.

If I put a 30dB attenuator right at the antenna connector of the Kenwood radio the issue is completely eliminated. The radio can be laying right over all the cables and still the VOX works properly.

With the attenuator in place the Kenwood still draws the same current, but only 1/1000 of the original RF power is radiated by the antenna.

With 6dB attenuator the issue is MUCH reduced compared to full TX power but not completely eliminated.

 

Also, the further from "Pro" I place the Kenwood, the less severe the issue gets. Unfortunately, for this specific installation placing the radio far away from the Pro is not an option.

 

Tom, this might not be something you can share with us but I;m still going to ask.

Can you tell us what is the FUNCTIONAL difference between parts 102 and 1402? Is there any RF filtering or by-pass capacitors or any such circuitry inside the faux batter pack of the 1402?

 

Also, there are 0402 bypass capacitors on all the in/out signals right at the I/O pins of the Autocom board. What's the value of those capacitors?

Since I know my issue is the ~450MHz signal from the radio, maybe I can replace the original caps with value that's more appropriate for this specific frequency.

 

Very good suggestions regarding the antenna placement.

 

I'm an electrical engineer by trade and have been designing and debugging RF equipment like cell phones and WiFi devices for the past 15 years.

I can make this work, I know it. It's just that I already do this stuff for work for close to 12 hours a day, the less I HAVE TO do it at home the better

 

Thanks again Tom!

 

 

[edit]

The US TK-3101 radios' transmit power is set to 2.0W and at that power level the input current is very close to 1A.

I wonder if European Kenwoods are set to lower TX Pout.

 

Last night I hooked up a programming cable to the radios and browsed through the menus in the Kenwood programming software.

There doesn't seem to be a way to select a lower TX power.

 

--

Mikko

[Tom B]

Mikko

 

I have to agree with your great reply, I know that RFI at high output levels close to the control unit can cause the auto-VOX to ramp up. The single BGNS controls both the auto-VOX level and also the auto-volume level circuits

 

The 0402 caps are 10pF, however if you test again but also with music playing you may find that the automatic volume also ramps up when the VOX ramps up, and if so then I would suspect that the RF is interfering with the BGNS or its yellow wire in the riders lead and/or infecting the auto level control filter circuit, and/or the AC to DC converter circuit which provides the DC variation (variable threshold point) to the comparator for the VOX.

 

It seems you know your stuff, and when it comes to RFI you probably know more than I do, so well done for that. Unfortunately I am not at liberty anymore to provide you with circuit details of a product I designed that someone else has now inherited from me, otherwise I would send a copy of that section of circuit for you to understand how I designed it to work, and with that you could perhaps play with it to see if you could tune it to better reject RFI, which could help others as well as you.

 

I will PM you some additional notes of what you may check to help pin-point where to try adding filters.

 

Tom

 

edit; You could switch the Pro into manual VOX mode, which may help?

[FlyingFinn]

This is very, very good information. Tom thanks for helping out.

 

...and/or the AC to DC converter circuit which provides the DC variation (variable threshold point) to the comparator for the VOX.

 

As soon as I read that part I couldn't help but to think that's probably where the RFI does its dirty job. RFI gets rectified into DC at the same circuit that rectifies the audio from BGNS into a DC for the VOX comparator. Detector is a detector....

 

What I need to accomplish now is to

1) Choke the RFI off the cables entering the Pro

2) bypass the residual RFI level to GND before it reaches the detector circuit.

 

Oh, that manual VOX level setting is a good idea.

 

--

Mikko

[FlyingFinn]

[Penforhire]

Tom, thanks for explaining VOX bounce! I never knew exactly why that happens with the TK.

 

I do not doubt your comments about the Auto-c speakers being loud enough when correctly positioned but it is not a piece of cake to reposition them in every helmet design.

[KDeline]

Without getting into a long story, I tried that exact settup when I burned out a PRO-7 a few years ago and had the same problems you are having. At the time I stumped Top Gear, so I found a used PRO-7 on ebay and have used it since. Never could get the Pro-AVI to work with the TK-3101, but the PRO-7 works well, in fact I have them strapped together in the tankbag. Now I wonder if I was having the same problem you were.

[FlyingFinn]

At the time I stumped Top Gear, so I found a used PRO-7 on ebay and have used it since. Never could get the Pro-AVI to work with the TK-3101, but the PRO-7 works well, in fact I have them strapped together in the tankbag. Now I wonder if I was having the same problem you were.

 

Since the Pro-AVI was the first model with auto VOX (uses the BGNS to detect noise level) it does make sense that PRO-7 would not have this problem.

 

From the testing I've done so far (and I have more HW ordered to debug this further) it does really appear as is RFI gets to the BGNS detector circuit and that jacks up the VOX level to too high. Without auto VOX level and auto volume level this issue is not there.

 

I have some ferrite beads ordered and I'll also take one of the Pro units to my work over the weekend to work on it in a real lab.

I'll try to come up with a fix that would be easy to replicate by others who have same issue with tightly packed radio installations. Ideally I could put together "a kit" that would be easy to install by anyone.

 

--

Mikko

[FlyingFinn]

Spent most of the afternoon today in the RF lab testing and trying to find a solution to the RFI issue. It seems there are multiple ingress points for the RF energy from the radio to enter the Autocom.

That means the an "absolute fix" to the issue is nor simple to implement nor easy to find.

I tried all sorts of RF bypassing, shielding, RF chokes on the cables, RF absorbing material I got from Camille, copper lining the Autocom box.... nothing really fixed it.

 

I did find a workable solution though. Most RFI seems to enter the Pro-AVI via the external PTT button and power cabling (Part 1456). Correct type of ferrite beads on those wires helps a lot.

Some RFI enters also via the headset cables. Ferrite beads over those wires helps too. Amidon ferrite materials #43 and #61 work well the GMRS frequency. I ended up using a mixture of both materials.

 

And simply running the riders headset and power cables away from the antenna makes a big difference.

 

Another point worth mentioning here is the TX power of Kenwood TK3101.

It is supposed to set to 2W ( at leas the US models) but I measured almost 3.5W. The difference comes from the TK3101 battery voltage.

 

The Kenwood battery has a nominal voltage of 7.2V, at that voltage the TX power is very close to 2W. As it's usually done, also in these radios the TX Power Amplifier runs directly from the batter voltage without any further regulation.

Pro-AVI puts out 9V to the bike-to-bike radios and at that voltage level the Kenwood's transmit power is 3.5W. That is almost double what these radios are supposed to transmit. I think the switching voltage regulator that Tom designed into the radio power adapters of the new Logic series is an excellent idea.

 

I just made a "battery eliminator" for myself that drops the 9V down to 7.5V with a linear regulator. It's a bit of waste of power but keeps the Kenwood transmitting at intended power level.

 

I did not find a way to re-program the power setting in the Kenwood.

 

--

Mikko