Experience with first turn-on of PS

K8EZB
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Experience with first turn-on of PS

Postby K8EZB » Thu Mar 24, 2022 7:29 pm

Over the last 90 days I have been setting up a new station around an ANAN-7000DLE transceiver and Acom 1200S amp and companion Acom 04AT tuner. This station was up and running without significant glitches other than some minor pilot error early in this period, with the exception that PS was not fully implemented due to unavailability of a coupler with a suitable attenuator output. After reading many of the posts here re couplers, I decided to use a TelePost LPC501 coupler with an optional -50dB attenuator port, in part, because I will also use this coupler with a TelePost LP-700 Digital Station Monitor, and also reports here that others have found this coupler satisfactory for use with PS. The TP coupler arrived today and I have been doing a step by step bring-up of the station with PS and the amp turned on. I started with the amp in standby and advanced the 7000DLE Drive through several steps to confirm that what I was seeing for S-ATT values was reasonable . The amp was then put into operate mode and 7000DLE Drive set initially to a level that corresponds to about 100 watts out; Drive level was then advanced through several steps to 500 watts out while checking S-ATT levels at each step. Everything seemed reasonable and the S-ATT value at 500 watts was at 25. Based on using Scott’s advice and calculations from a previous post, this seems to suggest a near optimum level but higher than I expected with a 50dB attenuator. It would appear that the actual attenuation of the TP coupler is more like -43dB. This amp will be limited to 500 watts due to not having 240VAC power in the shack, so, from what I have seen so far, it appears that everything is pretty much as it should be, including Amp-View, Feedback, and Correcting indications, and RF waveform and trapezoid patterns on the LP-700. Any insights/suggestions much appreciated.

Rick
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Re: Experience with first turn-on of PS

Postby w-u-2-o » Thu Mar 24, 2022 7:49 pm

It sounds like you did a careful and meticulous job, Rick! Nothing more to add :)

If and when you get 240VAC in the shack, you can simply add a 6dB attenuator to the output of the TelePost coupler and be good to go.

Are you enjoying your super clean, razor sharp signal?
K8EZB
Posts: 78
Joined: Sat Oct 23, 2021 3:45 pm

Re: Experience with first turn-on of PS

Postby K8EZB » Thu Mar 24, 2022 8:00 pm

Are you enjoying your super clean, razor sharp signal?


It feels so good! 8-)

Thanks for the speedy response.

Rick
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K8EZB
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Re: Experience with first turn-on of PS

Postby K8EZB » Sat Mar 26, 2022 8:32 pm

Well .... I thought I was there with PS setup. Maybe, maybe not. I became curious as to why my initial calculations for the value of an external attenuator predicted an S-ATT level of 18, but I was actually seeing an S-ATT value of 25 at 500 watts. The most likely explanation I can invent is that my TelePost LPC501 -50 dB attenuation port is actually providing -43dBm of attenuation. If so, then using Scott's calculation method, S-ATT should be 25, which it is at 500 watts. So far, so good. Here is where I go off into the weeds. The power out of the attenuator port would be 57-43 = 14 dBm. This is in excess od the maximum of 13 dBm level allowed to avoid damaging the radio. So, until I have a better understanding of what is happening, I have added an external 5dBm attenuator which brings the S-ATT level down to 20 as expected, and presumably, the power at the AL7K port to 14-5=9 dBm. The operation of the S-ATT is still something of a mystery to me; If I am getting an S-ATT value of 25 with no external attenuator, can I still be exceeding the maximum power allowed at the AL7K port? Perhaps a simple answer but not yet seeing it. Next step is to measure the actual power out at the sampler port.

Rick
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Re: Experience with first turn-on of PS

Postby w-u-2-o » Sat Mar 26, 2022 10:09 pm

Rick,

Your math is exactly correct, just like everything else in this topic so far. Well done!

One tiny mistake: it's a 5dB attenuator, not a 5dBm attenuator ;)

And the answer is, yes you can exceed the maximum safe input level.

If you don't have the schematics of the 7000, you can just look at the schematics for the older radios (in the schematic section of the forum), they are practically identical. The first component that matters is the step attenuator itself. It is rated for a maximum input power level of +30dBm (an entire Watt!). After that is a low pass filter rated for +27dBm (half a Watt). But after that is the ADC preamp, and it's a bit more delicate. So while things will be OK if the step attenuator has a bunch of attenuation cranked in, it is conceivable that the step attenuator might be set to 0dB and then the ADC preamp will bear the full brunt of whatever is coming into the PureSignal feedback path, less a dB or two of other losses.

IMHO it's not worth taking that chance when PS works fine at +13dBm max. feedback level or a lot less, and adding an attenuator is cheap insurance.

73,

Scott
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Re: Experience with first turn-on of PS

Postby K8EZB » Sat Mar 26, 2022 10:14 pm

IMHO it's not worth taking that chance when PS works fine at +13dBm max. feedback level or a lot less, and adding an attenuator is cheap insurance.


So noted. Thanks for your response.

Rick
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