Description of the problem

After having unusual difficulty using the VX-7 for CTCSS repeater operation, I decided to investigate the CTCSS capabilities of the VX-7. Listening to the radios transmitting a CTCSS tone alone, it was clearly distorting audio within the normal voice frequencies. I decided to do a more thorough analysis of the frequencies present when transmitting CTCSS tones.

Test setup

Using the external mic connector, the mic pin was shorted on the transmitting radio, thus bypassing the internal condenser mic. The receiving radio was a Yaesu FT-530 going directly from speaker out into a Toshiba laptop line in. The squelch of the FT-530 was open to prevent changes in the DC bias. The transmitting radio cycled from highest to lowest tones. The VX-7 cannot change tones while transmitting, so non-transmitting portions were later removed from the wave file. Cool Edit was used for recording and frequency analysis. The recording is a 8 KHz 16 bit mono wave file, compressed to mp3 for listening below. Frequency analysis is done with a Blackmann-Harris window and 1024 bands. Jpegs of the spectrums are available below as well.

Spectrum Analysis

Two VX-7R samples with serial numbers beginning with 3I190427XX. The third image is from a VX-5 for comparison. Click on the small image for a full spectral graph.

VX-7 A	VX-7 B	VX-5
Note the large number of overtones and extraneous frequencies		Note the lack of overtones
Listen to this mp3	Listen to this mp3	Listen to this mp3

Results

As you can easily see and hear, both these VX-7's produced a very dirty CTCSS tone. Tones were present all across the spectrum, interfering with the audible region of the spectrum. The VX-5, on the other hand, produced very clean tones with few harmonics or extraneous tones. Very little was present above 500 Hz. I can only guess that a very dirty tone generator was used in these two VX-7's, and perhaps a filter removing frequencies above the standard CTCSS frequencies is missing or defective. This filtering appears evident in the VX-5. In any case, the dirty CTCSS tones of these 2 VX-7's make these radios difficult to listen to, and difficult to operate repeaters requiring CTCSS. I can only hope that this is a flaw specific to a few VX-7's, and that most VX-7's don't exhibit this poor behavior.

Additional Testing

After pondering this problem, I realized some better methods for performing these tests, and I became curious of other circumstances. The following spectral graphs and mp3's were taken in the same manner as before, but all original tests were re-done for consistency of levels in each of these tests. In addition, I measured silence and DTMF tones. The silence is part of the same sample as DTMF and is taken from immediately prior to the DTMF. From the silence, I generated an FFT filter and applied it to all files, so that the tones generated could be viewed with less inherent noise. The filtered samples are provided separate from the original samples. The original VX-7 CTCSS sample inclides the original noise between samples in order to provide it in its most original format. VX-7 tests were only done with VX-7 B, assuming that results would be comparable.

Several VX-7 owners with this problem have called Yaesu regarding the problem and been faxed the portion of the service manual relavent to the alignment menu. I did some adjustment of the PL deviation adjustment in the alignment menu, but a brief look at spectral analysis made it obvious that this did not reduce extraneous tones any more than it reduced the fundamental tone, thus this is not a viable solution, and samples are not provided.

Additional Results

These further tests re-emphasized the original results. From this analysis, it becomes clear that the VX-5 produces something similar to a square wave and passes it through a low pass filter at about 400 Hz. The VX-7, on the other hand, produces a very dirty signal including not only harmonics, but several other non-harmonic tones. in addition the VX-7 appears not to pass the tones through any filter. The DTMF tests were simply to look at another example of tone generation by the radio. The DTMF tones in the VX-5 are slightly cleaner than the VX-7, but the DTMF tones don't appear to be a problem with the VX-7.

Additional information can be found at http://home.comcast.net/~sllewd/vx7rupdates.htm. Apparantly, this is only a recent problem, as older VX-7s have not shows this problem.

After "Repairs"

We decided to ship the second VX-7 back for "repairs". Unfortunately, the results were suboptimal. While I am pleased to announce the problem was not worse, it certainly doesn't appear to be any better either. The equivilent test was performed on the returned radio to compare results. The results are as follows.

VX-7 B

Listen to this mp3

Second Repairs

We sent the radio back once more for repairs. This time, the radio was returned in much better condition. See the details below.

VX-7 B

Listen to this mp3