Yaesu: VX-7R CTCSS Hum

My newly-acquired vx-7r has the issue of making the sub-audible ctcss tone... audible. In the lower tones around 67.0 Hz, it is not noticeable, but up near 254.1 Hz, the tone almost drowns out my voice.

I read about this issue, so apparently it's not just me. Does anyone know of a mod, or fix that can get rid of this issue? I bought my radio online on eBay (yea, yea, I know), but other than the ctcss tones, the radio is in great condition and functions normally.

Any input is appreciated (especially a remedy).

I don't have a ready answer for you, but if you download the service manual, you may find a menu item that will allow you to reduce the CTCSS amplitude. I have three VX-7rs and have not noticed a problem with any of them.

Is the hum in your receiver or are other people hearing it on you when you transmit? If other people are hearing the tone when you transmit then it could be your radio is defective or somebody screwed with the alignment mode menu. If it's just a menu setting then like NZ4ZN said if you have the service manual you might be able to fix it if you also had access to a service monitor and set it to the correct level.

If it's only on your receiver it's probably because Yaesu, Icom, Kenwood and Alinco don't high pass filter the receive audio on their amateur products (I don't know if they do on their commercial products) and the like the cheap Chinese radios do.

Hum on transmit may be due to an antenna the radio is NOT happy with. Not un common these days with all those supposed to be antennas!

avascan522 said:

My newly-acquired vx-7r has the issue of making the sub-audible ctcss tone... audible. In the lower tones around 67.0 Hz, it is not noticeable, but up near 254.1 Hz, the tone almost drowns out my voice.

I read about this issue, so apparently it's not just me. Does anyone know of a mod, or fix that can get rid of this issue? I bought my radio online on eBay (yea, yea, I know), but other than the ctcss tones, the radio is in great condition and functions normally.

Any input is appreciated (especially a remedy).

Click to expand...

254.1Hz is high enough to be heard on many radios that don't have audio pass filters in them. I used to have access to a GMRS repeater that required a 254.1Hz PL tone. The UHF mobiles I was using at the time had a low cut feature on them that could be turned on in software to block that. When I originally set up the radios I'd never turned it on. When I added the GMRS repeater to the channels I had to specifically turn the low cut option on to block it.

So, the question would be, where are you hearing this, is it on a scanner, another amateur radio, or somewhere else?
Some lower end radios don't have the low cut feature in the audio path.

Doesn't necessarily sound like an issue with your radio. Sounds normal for those higher PL tones heard on lower end radios.

Do you need to have those high tones turned on ??

Thanks for the input.

1. nd5y: It is not on the receiving end. I am decoding tones just fine. The problem lies in transmitting the tones. Other radio operators hear a hum in my signal.

2. cmdrwill: I used several antennas and the hum was still there. Not an antenna problem.

3. mmckenna: I have tested this with an FT-60, a Motorola XPR 6550, and a digital trunking scanner. On all 3 devices, I heard the hum coming from my vx-7. This only happens when I am using T or TSQ. When I am using DCS or no tones, there is no hum.

3. NDRADIONUT: I don't "need" those high tones, but the hum is noticeable even on tones as low as 107.2. Several repeaters around me use 179.9 and 203.5, so I do need those tones.

avascan522 said:

3. mmckenna: I have tested this with an FT-60, a Motorola XPR 6550, and a digital trunking scanner. On all 3 devices, I heard the hum coming from my vx-7. This only happens when I am using T or TSQ. When I am using DCS or no tones, there is no hum.

3. NDRADIONUT: I don't "need" those high tones, but the hum is noticeable even on tones as low as 107.2. Several repeaters around me use 179.9 and 203.5, so I do need those tones.

Click to expand...

CTCSS tone deviation might be too high. You'd need to research how to test and adjust that for the specific radio. Not something you can do by ear, you need appropriate test equipment.

avascan522 said:

3. mmckenna: I have tested this with an FT-60, a Motorola XPR 6550, and a digital trunking scanner. On all 3 devices, I heard the hum coming from my vx-7. This only happens when I am using T or TSQ. When I am using DCS or no tones, there is no hum.

Click to expand...

The FT-60 and the scanner likely do not have the audio pass filtering to block this. Not uncommon for consumer/amateur grade equipment. Not surprising that they can hear it, even with a properly adjusted radio.

the fact that the XPR hears it would indicate it is an actual issue with the CTCSS tone deviation with your radio, however I've never set up any of the XPR radios, so not sure if it's even got the option for turning audio cut filters on and off. The other Motorola gear I've worked with usually has this by default.

So, the idea that you are hearing these high frequency CTCSS tones on the consumer grade gear isn't surprising on it's own.
The XPR passing it is what makes me think there really is an issue.

You'll need a service manual for your VX-7R and the appropriate tools to adjust it. Likely a oscilliscope would work, but an actual service monitor would be a better choice. Any chance it's still under warranty?

NZ4ZN said:

I don't have a ready answer for you, but if you download the service manual, you may find a menu item that will allow you to reduce the CTCSS amplitude...

Click to expand...

mmckenna said:

....You'll need a service manual for your VX-7R and the appropriate tools to adjust it. Likely a oscilliscope would work, but an actual service monitor would be a better choice...

Click to expand...

Click to expand...

Exactly. Easy download.

I didn't have time to elaborate when I first posted on this above, but here is some additional information:

Page 9 of the service manual discusses CTCSS and that it is mixed with the audio output. There are several intermediate amplifier stages, through which one can control gain of the tone, but would not isolate the voice modulation and thus would control voice deviation as well.

Page 13 describes how to adjust frequency deviation (rendering amplitude) of several reference tones for CTCSS operation. 254.1 is adjusted for .5 kHz deviation. There is a possibility that yours is greater than that.

If your radio was not bought new, it is possible someone mistakenly adjusted tone deviation upward in an effort to increase audio output. I had adjusted several of my VX-7Rs for slightly higher audio deviation to reduce the attenuation effects of the waterproofing membrane over the microphone port.

While mmckenna is 100% correct about using proper test equipment for any alignment/adjustments, this adjustment may be an exception. One could reduce tone deviation a little at a time while watching for minimum audibility with enough deviation to wake up the repeater. Make note of the original setting before changing anything.

And.. you tested the audio and tone deviation with a calibrated load and a service monitor?

By chance is the hum occuring on transmit while using a battery, or on a power supply? Just thought to ask, since no one asked yet? 73, n9zas

Sub audible tone

A lot of radios have 300 hz high pass filters to block low frequency tones in the audio. 270 hz is much closer to 300 hz than 67hz.