433MHz Polyclass RF Amplifier for phased-array | HP 8505A VNA

[@AllElectronicsChannel]

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[@rjordans]

Nice to see the vna in action, those old machines really do need a bit of understanding to properly use. Something that the newer ones also need for accurate operation but there it is usually less obvious to the user when there's all kind of fancy menus to help you around

[@AllElectronicsChannel]

Yep!

[@Nissar.A]

Very interesting topic.

[@SerialNumber-jm1sg]

Hi! Absolute happy looking you channel! Special thanks because of naming antenna both surnames of inventors, lats years most people call it just Yagi, however I was tough that it's is Uda-Yagi. Best regards, many thanks

[@gammaleader96]

very nice. As nice and well working these old VNAs are, I'm quite happy about the comfort that the newer models provide. But as has been already said, the amount of knowledge you get from needing to understand how the VNA works to be able to properly use it is very important and interesting. The input impedance looks really good, one nice "cheat" is to place a small resistive attenuator on the input to "force" it all the way where you want it. Not efficient but cheap and it works. The impedance of active devices really is an even blacker art than RF itself.

[@AllElectronicsChannel]

Hey man!! I have some videos in the queue before going to all the neat stuff you sent me.. Sorry for not posting yet!

[@gammaleader96]

@@AllElectronicsChannel Hey Gregory, no worries, take your time and do what you want to do. I like all of your videos since all of them have some interesting aspect to them so no worries there. ;)

[@omarakdh-xp4eo]

Welcome Don't forget it

[@WalidIssa]

Great videos. I have just gone through a lot of your videos and found them interesting. I am not a communication guy but really interested in finding a working simple circuit (made at home) for RF control transmittier and receiver for one bit or 4 bits over a few km and how to design an amplifier and choose an antenna to make it tens of km. I hope you can share some designs or resources and better if you could go through some videos designing and testing them

[@AllElectronicsChannel]

Welcome aboard!

[@WalidIssa]

So should I wait for them comming here and soon ?@@AllElectronicsChannel

[@JeffersonBuenoLab]

Excellent video...lots of information

[@AllElectronicsChannel]

Thanks!

[@ralvarezb78]

Love your videos, you have the level!!

[@AllElectronicsChannel]

Glad you like!

[@mpavlin969]

Hi, Great video about fundamental things. Thank you. You have new subscriber.

[@AllElectronicsChannel]

Welcome aboard!

[@proweb7271]

VERY VERY NICE VIDEO, THANK YOU !!!!!!!

[@AllElectronicsChannel]

Thanks man!

[@gabrielvigiano]

Nice video Gregory... u r awesome... keep going... =)

[@AllElectronicsChannel]

🤘🤘🤘 thanks man!

[@manuelminutello3027]

Very nice video! BTW, if you ever need replacements for that vna i have a unit for spare on the shelf

[@AllElectronicsChannel]

WOW!!! Amazing. Probably it have amazing parts to be used in projects also

[@Jorge-or3fr]

Great Gregory! Tell me if I feed it with lets say 20 mw input of a 433 mhz frecuency, how much RF can I obtain at the OUTPUT if I build it like you teach us? 😊 Cheers

[@AllElectronicsChannel]

Hi Jorge, thanks! I don't remember exactly the final specs. Maybe looking in the video you can see the overall gain of the amp

[@omsingharjit]

hey can you explain rf door bell circuit and its working it seems interesting because of its excellent range , stability and simplicity .

[@AllElectronicsChannel]

Nice idea!

[@petzhang3019]

Great video. 13:30 when change the bias, the impedance (I assumed that's the output impedance) change. You mentioned changed the common emitter preamp to common base preamp and then you get a almost constant output impedance with the various bias. Do you have the schematic how you change the preamp stage to common gate? Also when you mean poor isolation, what's the theory behind? Thank you for your knowledge

[@AllElectronicsChannel]

I don't have the schematics. The common base presents higher isolation because it doesn't suffer from the Miller Effect. I have a video about Miller effect here on the channel, take a look

[@angelodemichele]

Could you explain in future in details the RF amplifier circuit? How calculate inductor collector and what is it for? Thanks

[@AllElectronicsChannel]

Yep!! Basically it is a impedance matching network... I have videos about it.

[@nesmaster14]

RF electronics realtor :) 5:21

[@AllElectronicsChannel]

😂😂😂😂

[@estebanbriceno3190]

What is the serie of transistor that you used ?

[@AllElectronicsChannel]

BFR106 and 2SC3357.

[@like_cabezon3810]

The BW botons near the CRT are for resolution Bandwith or for Video Bandwith? what philosophy is used in the phase measurement of Those instruments I Q signals or the PFD widely used in the PLL? And it is able to measure group delay because to do that i supose that you have to get rid of the discontinuities of the phase vs freq Signal and then derivate the Signal?

[@AllElectronicsChannel]

The buttons are for resolution bandwidth, if I'm not mistaken. I think they use phase comparators like in PLLs. It also have a VERY complex PCB only for group delay, with derivators, phase compensators, using the linear signal from the sweep. Take a look at the service manual.. this device is a beast.

[@sli6635]

How can we measure output impedance

[@AllElectronicsChannel]

VNA!

[@sersheva]

Excellent video Gregory! I have a question how could you measure the possibility of oscillations with the vna? Like factor K that is usually predicted in simulators. Thanks a lot. Excellent work!

[@AllElectronicsChannel]

Good question! It is possible converting the polar readings to scalar S parameters and using conventional stability equations.

[@sersheva]

@@AllElectronicsChannel correct!, just is a little tedious because for each new bias point the S parameters are different, so we would have to recalculate each time to ensure stability, would be great if a equipment could be cheking the stability in real time or at least draw in the smith chart the stability circles before the flash hahaha. I think is better be sure making it unconditionally stable and then test. I sent a message to your ig!

[@AllElectronicsChannel]

Amazing!!

[@kmikeru]

Delay line? That's an obscure way to transmit BPSK!

[@AllElectronicsChannel]

wow!

[@kmikeru]

@@AllElectronicsChannel I didn't check the details but I suspect that's how electronically scanned radars function as the communication channel too.

[@kot_kot_kot5172]

Very nice amp! Did You measure the P1db of this amplifier?

[@AllElectronicsChannel]

Not yet, I will measure it. One thing I measured was very low efficiency, like 12% =[

[@kot_kot_kot5172]

@@AllElectronicsChannel Efficiency is a myth. Amplifier must amplify :D.

[@AllElectronicsChannel]

Hahahahahahha

[@tiborherman5471]

Why don't you place a series capacitor with 33 Ohm impedance instead of a 33 Ohm resistor? If it's a narrow band amplifier, wouldn't it be better to not sacrifice noise figure over broadband input impedance?

[@AllElectronicsChannel]

The resistor absorbs the power! A capacitor would reflect power back to the delay line.

[@tiborherman5471]

@@AllElectronicsChannel but only if it is not matched. If the impedance the delay line sees is matched to the line`s impedance, then the reflection is lower.

[@AllElectronicsChannel]

33 ohm if different than 33j! The capacitor adds series reactance, not resistance!

[@weinihao3632]

@@AllElectronicsChannel Then, to rephrase Tibors question: why didn't you place an LC matching network with 33 Ohm impedance instead of the 33 Ohm resistor?

[@tiborherman5471]

@@weinihao3632 that's actually the real question I should have asked.

[@mr.fantomas7726]

I saw a better amplifier, with constsnt current base (teperature compensated) for low noise.

[@AllElectronicsChannel]

Interesting!

[@mr.fantomas7726]

@@AllElectronicsChannel with 2x BFR91A and 2x BC177 , 70cm band and LC Filter .

[@AllElectronicsChannel]

If you have the schematic, share with us 😁🙏🏼

[@mr.fantomas7726]

@@AllElectronicsChannel BFR91A Ic=5mA Nf=1.5dB, used in RF wideband antenna for analog TV . Look for datasheet BFR91A ,Smith Diagram ,very interesting ,Fmax above 2GHz for sure.