Anytone AT-6666 High SWR

[llilillill]

When it rains, it pours. Now I'm having a strange problem with my Anytone AT-6666... high SWR and poor receive, but only on channel 19. All other frequencies and USB/LSB work just fine. Sometimes the SWR protect comes on. Any ideas what could cause this? Software glitch?

 

[M0GVZ]

You have to use software to program the channel names and their frequencies into memories in this radio to get it to work "like a CB". I'm betting my bottom dollar that the entry for Ch19 has got corrupted so instead of being on say 27.185MHz it may be on 30.000MHz or some random figure so even though the display says Ch19 it isn't on that channel or anywhere near your antenna is tuned for. That would explain why it is only that one channel.

Change to VFO mode, tune to 27.185MHz and see if it runs OK. If it does then it points to the memory entry corruption being the issue.

To be honest that wouldn't come as a surprise because if you've a lot of common mode RFI due to a poor RF ground, given that Ch19 is the one most used that is likely to be the one memory location likely to get corrupted due to the common mode RFI.

Get the programming software and lead and check.

 

[sp5it]

Does it happen on dummy load?

 

[llilillill]

You have to use software to program the channel names and their frequencies into memories in this radio to get it to work "like a CB". I'm betting my bottom dollar that the entry for Ch19 has got corrupted so instead of being on say 27.185MHz it may be on 30.000MHz or some random figure so even though the display says Ch19 it isn't on that channel or anywhere near your antenna is tuned for. That would explain why it is only that one channel.

Change to VFO mode, tune to 27.185MHz and see if it runs OK. If it does then it points to the memory entry corruption being the issue.

To be honest that wouldn't come as a surprise because if you've a lot of common mode RFI due to a poor RF ground, given that Ch19 is the one most used that is likely to be the one memory location likely to get corrupted due to the common mode RFI.

Get the programming software and lead and check.

That is exactly what happened. Channel 19 was set to 28.280.

To reset it, all I had to do was push the 'freq' button, dial it back to 27.185 and then push the 'freq' button again to display 19. When I pushed freq again after flipping through channels, it stayed.

To me, that's kind of a stupid way to program it... too easy to mess up "channels".

At any rate, I won't be using the channel mode anymore. I don't need the FCC kicking down my door for accidentally keying up somewhere I shouldn't be.

 

[llilillill]

Does it happen on dummy load?

No, but M0GVZ nailed it. It was corrupted memory.

On the subject of common mode currents, I have this radio installed in my car with a mag mount Wilson in the center of the roof (Toyota Corolla). Are mag mounts prone to common mode?

 

[sp5it]

In most of the cases with magnet coax is counterpoise, not a roof.
Mike

 

[llilillill]

In most of the cases with magnet coax is counterpoise, not a roof.
Mike

I was always under the impression that mag mounts were capacitively coupled to the metal underneath?

 

[Riverman]

I was always under the impression that mag mounts were capacitively coupled to the metal underneath?

Rest easy, IIiI.
Mike is pulling your leg.

 

[M0GVZ]

I was always under the impression that mag mounts were capacitively coupled to the metal underneath?

Yeah, it is. Not a problem if you're running legal power but is when you start ramping it up. The smaller the magmount the lower the power before it becomes an issue.

I can't recommend drilling holes in the roof enough and doing bonding as per the bonding page at www.k0bg.com. 99% of noise issues will be solved. I can drive out in the countryside and with the engine running I have S0 of noise. Only downside is you end up finding you have to cut a few inches off every antenna you fit due to the higher efficiency of your RF ground.

Magmounts are OK for temporary installs like on a hire car but they're not designed for long term use. Use them long term and you get paint discolouration because the paint under the mount fades at a slower rate than the rest of the car, you get scratches in the paint from the metallic particles from brake pads which stick to the coax and scratch the roof as it flaps about in the wind, you get SWR issues as the coax gets pinched in the door/trunk and there is a high risk of it coming off if your antenna hits an overhead object.

Even a lip mount is better.

 

[llilillill]

Yeah, it is. Not a problem if you're running legal power but is when you start ramping it up. The smaller the magmount the lower the power before it becomes an issue.

I can't recommend drilling holes in the roof enough and doing bonding as per the bonding page at www.k0bg.com. 99% of noise issues will be solved. I can drive out in the countryside and with the engine running I have S0 of noise. Only downside is you end up finding you have to cut a few inches off every antenna you fit due to the higher efficiency of your RF ground.

Magmounts are OK for temporary installs like on a hire car but they're not designed for long term use. Use them long term and you get paint discolouration because the paint under the mount fades at a slower rate than the rest of the car, you get scratches in the paint from the metallic particles from brake pads which stick to the coax and scratch the roof as it flaps about in the wind, you get SWR issues as the coax gets pinched in the door/trunk and there is a high risk of it coming off if your antenna hits an overhead object.

Even a lip mount is better.

I may put a lip mount on it but a hole through the roof is a definite no. I did that on a Ford Escort that had a flimsy roof like this Corolla. Eventually, the antenna flexing the roof in the wind caused the roof to crack all the way across.

I put the radio in my truck and it doesn't perform nearly as good as it does in the car. That Lil Wil is very narrow banded. I actually have to lower the whip a little bit to talk on 38LSB. I hear all kind of stuff when it's in the car that I can't hear in my truck.

 

[M0GVZ]

Usually having to shorten an antenna is a sign of an improved RF ground so generally a good thing. Unfortunately because of the way antennas work a short one is most likely to have narrow bandwidth.

Antennas have three characteristics, size, efficiency and bandwidth. You can have any two of those characteristics you'd like as a positive but you'll lose the third as a positive. So for example you can have a very efficient antenna with a wide bandwidth but it won't be small. You can have a small antenna with high efficiency but it'll have low bandwidth or you can have a small antenna with wide bandwidth but you'll have low efficiency.

 

[llilillill]

Usually having to shorten an antenna is a sign of an improved RF ground so generally a good thing. Unfortunately because of the way antennas work a short one is most likely to have narrow bandwidth.

Antennas have three characteristics, size, efficiency and bandwidth. You can have any two of those characteristics you'd like as a positive but you'll lose the third as a positive. So for example you can have a very efficient antenna with a wide bandwidth but it won't be small. You can have a small antenna with high efficiency but it'll have low bandwidth or you can have a small antenna with wide bandwidth but you'll have low efficiency.

I am still learning about antennas. I got myself a RigExpert AA-54 and have been using it to learn how various antennas perform. It makes it pretty easy to see how changing length, grounds, coax, etc. affect the different parameters.

My next project is to find a puck mount and try my hand at impedance matching.

 

[M0GVZ]

I am still learning about antennas. I got myself a RigExpert AA-54 and have been using it to learn how various antennas perform. It makes it pretty easy to see how changing length, grounds, coax, etc. affect the different parameters.

If changing the length of coax alters the SWR this is a strong indicator you have a poor RF ground and it is in fact the coax that is being used to make up for the missing ground.

Try another experiment. I referred you to k0bg.com and the bonding page I think, if not take a look. You can monitor how bonding improves the RF ground and what effect improving the RF ground has on an antenna system. Firstly before you start take a note of what frequency the lowest SWR is and where the value of X is 0 or closest to 0. Next do some bonding, maybe the trunk to the body or the hood to the body. Without adjusting the antenna measure the frequency of where the lowest SWR is and again where X=0 and you should see it has lowered. This is proof of an improvement of the efficiency of your RF ground. I use a fixed mount in the centre of the roof and have bonded everything. Every CB antenna I put on my car out of the box with the whip adjusted to its shortest length is usually tuned on 25MHz and I have to cut around 3-4" off the whip to get it to 27MHz. Before I did that and when using a magmount they'd all be around 27MHz out of the box as you'd expect.

If you have a whip without any coils etc that you can use with your mount you can also look at the value of R which is the feedpoint impedance. The feedpoint impedance of a quarter wave over a perfect ground is 36.8 Ohms at resonance (where X=0). Anything other than that is indicating ground losses. For experimentation it doesn't matter that the whip isn't a quarter wave for 27MHz, just take the reading of R at whatever frequency X=0. As you improve the grounding you'll see R get closer to 36.8 Ohms and again you'll notice a lowering in frequency where X=0. However be aware that the value is only valid for the resonant frequency of that antenna so if you're using anything other than a 102" whip it won't be valid for 27MHz.

 

[my2995dx]

I have the same trouble but it's on all cb channels.I had a hard time getting it set had to cut over 1/2 off the wip of the sirio mag mount had it set to 1.3 last month it worked fine now nothing a few times going through the drive through at a coffee joint it would scrape and a few low branch's but now I can't get it set back to 1.3

 

[Robert Foster]

When it rains, it pours. Now I'm having a strange problem with my Anytone AT-6666... high SWR and poor receive, but only on channel 19. All other frequencies and USB/LSB work just fine. Sometimes the SWR protect comes on. Any ideas what could cause this? Software glitch?

Just do a reset from program button on radio go to reset push and it will put all channel's back to where they are supose to be. May have to turn hicut Nb automatic squelch asq and so on but will fix channel's and frequency matching.