PURE SIGNAL FEEDBACK

[Probir]

I will be shortly deploy Pure signal with HL2.

 

I was just thinking how we can provide the feedback signal at RF3 in different POWER output from 10 watt to 500 watt.

 

What is the min. RF power we need to feed to THE HL2 receiver port at RF3. Will be a great help if one explains

 

 

73

PROBIR VU2BQF

[Steve Haynal]

Hi Probir,

PureSignal can work with just stray RF pickup to the RX, so power requirements are low. There have been some experiments with a small feedback board with attenuator. You must still have an external coupler to extract some power from your TX signal. Search this group for PureSignal for more details.

73,

Steve

kf7o

[Joe LB1HI]

Hi Probir,

The maximum allowable level of absolute voltage ratings (at 400 Ohm impedance) connected to the RX ADC AD9866 input is specified in the datasheet. You can calculate how the power value brought to HL2 will generate this voltage. Of course, it is necessary to take into account the increase in voltage beyond T2 as a result of impedance transforming to a higher one. But in practice, we don't need it.

Because the MAX value is a parameter of little use because much earlier before reaching this level comes to ADC overload and clipping.

A practical way is to determine the value of an additional attenuator experimentally. By plugging the step attenuator in series with the sampler signal and starting from a high attenuation value, gradually reduce it until Pure Signal works properly.

The pure signal function signals the correct level of the received signal by changing color. Green indicates the correct optimal level.

Theoretically, you can also measure/calculate the signal level from the sampler in dBm but remember that there is still internal crosstalk in HL that mixes with the signal from the sampler

You can buy a sampler or build it yourself.

After finding the required attenuation value (sum of sampler plus additional step attenuator) for the pure signal to work properly at 10 Watt and at the same time we know that when increasing the power to 50 Watt, the gain will be PR 5 - 7dB.

With an increase to 200 Watt PR20 = 13 dB

 and at 500 Watt PR50 = 17 dB

So as you can see by increasing from 10 to 500 Watt there will be an increase in the signal level from the sampler by max 17 dB. And this is in the area of ​​automatic S-ATT correction.

Even if you build a not very linear sampler in terms of att/frequency, it is still a reserve and it will be OK if it falls within the range of S-ATT automatic.

In OpenHPSDR-PowerSDR mRX PS it is from 0 to 31 (which corresponds to the LNA level of 20dB at S-ATT = 0 to -12dB at S-ATT = 31) (LNA in ADC has a range of −12 dB to +48 dB)

When constructing a sampler, its constructions should be adapted to power ratings. (In your case, 500 Watt)

It is also worth paying attention to the voltage rating if someone uses a sampler directly after the tube amplifier. In tube amplifiers, high impedance (read voltage) may appear during tuning.

The information on these pages will definitely help you choose the sampler design.
1. http://www.collinsradio.org/wp-content/uploads/2015/05/Build-a-Quality-RF-Power-Sampler-Jackson.pdf 

2. https://sites.google.com/view/vk1hw/homebrew/taps/rf-sampler 

73, Joe
LB1HI