If I hook up a HF ultra-wideband (UWB) amplifier with a transmitting UWB antenna (out) and a receiving UWB antenna (in)

Thread Starter

genekuli

Joined Oct 21, 2018
103
If I hook up a HF ultra-wideband (UWB) amplifier with a transmitting UWB antenna (out) and a receiving UWB antenna (in) and have the antennas very close (few inches) to each other inside a metal box (~40cm) so as to produce a feedback loop, then due to the noise and harmonics of the over-driven amplifier clipped-waveform, it would then add more frequencies with each loop, resulting in an exponential growth in the amount of frequencies (to the limit of the amplifier and antennas), is that correct?
 

Papabravo

Joined Feb 24, 2006
16,118
If I hook up a HF ultra-wideband (UWB) amplifier with a transmitting UWB antenna (out) and a receiving UWB antenna (in) and have the antennas very close (few inches) to each other inside a metal box (~40cm) so as to produce a feedback loop, then due to the noise and harmonics of the over-driven amplifier clipped-waveform, it would then add more frequencies with each loop, resulting in an exponential growth in the amount of frequencies (to the limit of the amplifier and antennas), is that correct?
I don't think that is correct. Each of the systems you mentioned has finite limits. The amplitude will cannot grow exponentially because the power supply will limit the maximum amplitude. The number of frequencies cannot grow without limit since electronic amplifiers cannot generate, transmit, or receive light in the visible spectrum. At some point on the spectrum analyzer display the remaining signals will descend into the noise floor where they become indistinguishable from signals from all other sources.
 

Thread Starter

genekuli

Joined Oct 21, 2018
103
yes, it is limited in the ways you mentioned, but i am just trying to work out if this setup would even do anything at all? would it overdrive the amp and clip the signal and generate lots of frequencies?
i just do not have any experience in the use of the equipment to even know if it is possible to set up such a feedback?
 
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Papabravo

Joined Feb 24, 2006
16,118
yes, it is limited in the ways you mentioned, but i am just trying to work out if this setup would even do anything at all? would it overdrive the amp and clip the signal and generate lots of frequencies?
i just do not have any experience in the use of the equipment to even know if it is possible to set up such a feedback?
I can't see any potential for it doing anything interesting at all.
 

Audioguru again

Joined Oct 21, 2019
3,177
Positive feedback oscillation usually occurs at the frequency where the gain is the highest. Your antennas are small so the high gain will occur at a very high frequency then the clipping harmonics with odd frequencies will reach as high as the gain allows. There might not be many frequencies.
 

Thread Starter

genekuli

Joined Oct 21, 2018
103
Positive feedback oscillation usually occurs at the frequency where the gain is the highest. Your antennas are small so the high gain will occur at a very high frequency then the clipping harmonics with odd frequencies will reach as high as the gain allows. There might not be many frequencies.
but with each loop of amplification and clipping, that surely will keep adding new frequencies and keep the present ones right? resulting in more and more frequencies
 

nsaspook

Joined Aug 27, 2009
8,382
but with each loop of amplification and clipping, that surely will keep adding new frequencies and keep the present ones right? resulting in more and more frequencies
The nature of UWB signal is it's very fast edges and very short duration like a spark-gap signal. It's not something you get from feedback phase-shifting systems normally. The narrower the pulse, the wider the bandwidth. The low energy density signal means it's very non-continuous non-sinusoidal (a Gaussian monocycle) and is more like random noise.
http://wcsp.eng.usf.edu/UWB_Testbed_Docs/RedRinging.pdf
On-the-left-The-fourth-order-Gaussian-monocycle-pulse-0175-ns-used-for-the.png
http://www.comlab.hut.fi/opetus/333/reports/Yang_Principles_of_Ultra_Wideband_communications.pdf
 
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Audioguru again

Joined Oct 21, 2019
3,177
He did not say "pulse generator". Instead he said "amplifier". The amplifier or receiver probably produces symmetrical clipping at the most sensitive frequency of the antennas, amplifier and receiver with only a few odd-numbered harmonics.
 

Thread Starter

genekuli

Joined Oct 21, 2018
103
The moment it begins to oscillate then it produces a sqauarish waveform with a few harmonics. More frequencies will not be added.
but is it not that the square waveform is only made through lots of frequencies and they will stay right or does it just become one square frequency?
 

Thread Starter

genekuli

Joined Oct 21, 2018
103
He did not say "pulse generator". Instead he said "amplifier". The amplifier or receiver probably produces symmetrical clipping at the most sensitive frequency of the antennas, amplifier and receiver with only a few odd-numbered harmonics.
so what do you think then would happen
if I hook up a HF ultra-wideband (UWB) amplifier with a transmitting UWB antenna (out) and a receiving UWB antenna (in) ?
 
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Thread Starter

genekuli

Joined Oct 21, 2018
103
The nature of UWB signal is it's very fast edges and very short duration like a spark-gap signal. It's not something you get from feedback phase-shifting systems normally. The narrower the pulse, the wider the bandwidth. The low energy density signal means it's very non-continuous non-sinusoidal (a Gaussian monocycle) and is more like random noise.
http://wcsp.eng.usf.edu/UWB_Testbed_Docs/RedRinging.pdf
View attachment 228360
http://www.comlab.hut.fi/opetus/333/reports/Yang_Principles_of_Ultra_Wideband_communications.pdf
so what do you think then would happen if I hook up a HF ultra-wideband (UWB) amplifier with a transmitting UWB antenna (out) and a receiving UWB antenna (in) ?
 

nsaspook

Joined Aug 27, 2009
8,382
He did not say "pulse generator". Instead he said "amplifier". The amplifier or receiver probably produces symmetrical clipping at the most sensitive frequency of the antennas, amplifier and receiver with only a few odd-numbered harmonics.
I agree with you. Nothing special will happen because the UWB amplifier specification is needed to pass the generated UWB pulse signal. The amplifier, in some strange input to output feedback mode will most likely have a Parasitic oscillation at some pole frequency(s) where there is the phase-shift to generate a clipped set of waveforms.
https://www.matec-conferences.org/articles/matecconf/pdf/2018/32/matecconf_smima2018_02032.pdf
 

Audioguru again

Joined Oct 21, 2019
3,177
I think that a UWB transmitter and receiver will have a flat frequency response then will have a peak at a high frequency, then higher frequencies will drop off. They will oscillate at the peak and cause symmetrical clipping which is full of odd numbered harmonics. But the drop in the frequency response at the very high frequencies will limit the odd harmonics to only a few.
 

nsaspook

Joined Aug 27, 2009
8,382
I think that a UWB transmitter and receiver will have a flat frequency response then will have a peak at a high frequency, then higher frequencies will drop off. They will oscillate at the peak and cause symmetrical clipping which is full of odd numbered harmonics. But the drop in the frequency response at the very high frequencies will limit the odd harmonics to only a few.
That's generally what will happen if the gain device has a high cutoff frequency. For a HF tube amplifier the Parasitic oscillation might be in the UHF range where there is adequate gain at the Parasitic fundamental to oscillate but much less at harmonics. The gain device inability to switch at X rate limits (low pass filter) the harmonics to only a few.
 
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