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Author Topic: RTS / Telex BTR-800 Wireless com  (Read 1293 times)

Jason Glass

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Re: RTS / Telex BTR-800 Wireless com
« Reply #10 on: July 27, 2017, 06:13:50 pm »

Speaking for Professional Wireless, you cannot put the UV-1G into the GX series. The AGC circuit constantly chases the AM signal trying to compensate for the modulation. This directly impacts audio quality of the system. The GX series was designed for fixed amplitude signals, e.g. FM.

Cameron
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Hey, Cam

Just for giggles, we tested 2 channels of Lectro Duet through a GX-8 today and got interesting results. At all three Duet power levels, the combiner added 6 sidebands to the carrier, distorting the 200kHz channel bandwidth to 1.4MHz. Yeow! Strangely, switching from normal to high power on the GX had no measurable effect whatsoever on the amplitude or spectral shape. Even more strangely, the system still functioned fine and walk testing showed the range to be commensurate with 10mW output routed directly from the Duet to the same test antenna.

Of course I know that these were severe experimental conditions well outside of design tolerances and intended use, but I didn't expect the system to work as well as it did with AGC trying to squash AM.

Giggles we wanted, and giggles we got!

EDIT, CORRECTIONS:

The number of distortion sidebands that we measured was actually 4, not 6, and their bandwidth was around 125kHz, not 200 kHz, making the total distorted channel bandwidth near 700kHz, not 1.4MHz.  Uugh.

10mW input actually generated less distortion and its output power within a 200kHz channel mask was around 3dB lower than 25mW and 50mW input levels, as one might expect.  However, 50mW input pushed power to the outer sidebands and the channel power was slightly lower than 25mW, as one might expect from a saturated amp.

Since the Devil's in the details, my post above was quite incorrect and I apologize for causing confusion.

« Last Edit: July 28, 2017, 12:34:56 pm by Jason Glass »
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Cameron Stuckey

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Re: RTS / Telex BTR-800 Wireless com
« Reply #11 on: July 27, 2017, 08:47:39 pm »

...    At all three Duet power levels, the combiner added 6 sidebands to the carrier, distorting the 200kHz channel bandwidth to 1.4MHz.    ...   Even more strangely, the system still functioned fine and walk testing showed the range to be commensurate with 10mW output routed directly from the Duet to the same test antenna.

To confirm, you experienced that distortion and distances with 10mW direct and 10mW into the GX? Spec for the input power of a GX is 20mW-100mW. If the Duet was at 10mW into the GX I'm not surprised things got a little funky.
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Jason Glass

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Re: RTS / Telex BTR-800 Wireless com
« Reply #12 on: July 27, 2017, 09:07:41 pm »

To confirm, you experienced that distortion and distances with 10mW direct and 10mW into the GX? Spec for the input power of a GX is 20mW-100mW. If the Duet was at 10mW into the GX I'm not surprised things got a little funky.
The spectral signature and amplitude from the GX-8 output were identical with input signal strengths of 10mW, 25mW, and 50mW.

EDIT, CORRECTIONS:

The number of distortion sidebands that we measured was actually 4, not 6, and their bandwidth was around 125kHz, not 200 kHz, making the total distorted channel bandwidth near 700kHz, not 1.4MHz.  Uugh.

10mW input actually generated less distortion and its output power within a 200kHz channel mask was around 3dB lower than 25mW and 50mW input levels, as one might expect.  However, 50mW input pushed power to the outer sidebands and the channel power was slightly lower than 25mW, as one might expect from a saturated amp.

Since the Devil's in the details, my post above was quite incorrect and I apologize for causing confusion.
« Last Edit: July 28, 2017, 12:35:53 pm by Jason Glass »
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Henry Cohen

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Re: RTS / Telex BTR-800 Wireless com
« Reply #13 on: July 28, 2017, 11:31:57 am »

The spectral signature and amplitude from the GX-8 output were identical with input signal strengths of 10mW, 25mW, and 50mW.

I'm not surprised either. I would presume the composite energy from the 8PSK carrier, even at the 10mW setting, is close enough to that of a 100mW FM CW carrier such that not only is there no defined [relatively] narrow band carrier for the AGC to lock on to, but the amplifier stage is in saturation from the start.
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Henry Cohen

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Jason Glass

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Re: RTS / Telex BTR-800 Wireless com
« Reply #14 on: July 28, 2017, 12:32:34 pm »

I'm not surprised either. I would presume the composite energy from the 8PSK carrier, even at the 10mW setting, is close enough to that of a 100mW FM CW carrier such that not only is there no defined [relatively] narrow band carrier for the AGC to lock on to, but the amplifier stage is in saturation from the start.

Understood.  BTW, I must make some corrections below about the details, as my memory fuzzed badly when I posted. I went back and compared SA screen shots of the different test conditions, which I have attached to this post.

The number of distortion sidebands that we measured was actually 4, not 6, and their bandwidth was around 125kHz, not 200 kHz, making the total distorted channel bandwidth near 700kHz, not 1.4MHz.  Uugh.

10mW input actually generated less distortion and its output power within a 200kHz channel mask was around 3dB lower than 25mW and 50mW input levels, as one might expect.  However, 50mW input pushed power to the outer sidebands and the channel power was slightly lower than 25mW, as one might expect from a saturated amp.

Since the Devil's in the details, my post above was quite incorrect and I apologize for causing confusion.  I'll go back and add these corrections as an addendum to the post.

I'm still stunned that the system sounded fine under these conditions.  In fact we pushed the limits and tuned two channels at 200kHz spacing (Lectro recommends no less than 400kHz), through a PA821A, and the audio didn't even slightly glitch.  I'd very much like to test 24 mixes of these working together!
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