HF Transmitter #09 - Directional Coupler, LPF & Antenna Relay

[@R2AUK]

Great video, many thanks! Personally I ended up using Stockton bridge (aka Tandem Match) based on a BN61-202 binocular with germanium diodes (1N34 or a local equivalent D311) in my projects. A good instruction of building this circuit can be found in W1FB’s Design Notebook, although the author uses two ferrite cores instead of a binocular. The advantage of using a binocular is that both cores have exactly the same permeability which reduces the error. The voltage can be sampled directly without any opamps and the precision is excellent regardless of the power level and SWR.

[@waltbohlman1825]

Hi Darin
Great sselection of topics. Refurbishing old boat anchors is always quite interesting. I have many more than I will get to. Your technical levelis just perfict. I have not used Spice in a long time , I seem to be able to do most things with Microwave Office. Currently working on 222 grear in hopes of doing EME. Keep up the good work.
Best Regards
Walt K3BPP

[@ohmschool]

Very Nice! TX/RX relay in your schematic has an operate time of 15ms which is probably a bit too slow for QSK CW. Replacing the G2RL relay with a PIN Diode Switch, or replacing G2RL with a relay that has a much faster operating time could be future options to enable full duplex CW.

[@levelupeelab]

Thanks for the tip!

[@t1d100]

Excellent.

[@fluffycookie519]

Did you consider using a factory matched diode pair? Is possible that your error is due to different IV curves on two separate diodes

[@levelupeelab]

It is possible but not highly likely. The diodes I used were in sequential order on the reel, so part to part variation should have been very small.

[@amirb715]

I think instead of going through all of that investigation of the peak detector circuit, you could have simply used a zero drop peak detector which basically integrates the detector diode and the capacitor in the opamp feedback. This is a good video about that th-cam.com/video/Fn5kHhNRsz0/w-d-xo.html

[@4youian]

You would then need your opamp to be responsive at RF frequencies, increasing the cost.

[@amirb715]

@@4youian LMC6482 (dual, GBW=1.5MHz)=C$2.75 , LMH6658MAX (dual, GBP=140MHz, 3dB BW=290MHZ)=C$2.95 works with 12V single supply too. I am 100% sure there are more examples in the same price range

[@4youian]

@@amirb715 worth a try in ltspice

[@levelupeelab]

Thanks for the tip! I was familiar with Alan's video already, but I didn't do any further product searching for an op amp with GBP high enough for Amateur HF application. It does look like the 6658 would fit the bill. If I revisit this topic in the future, I'll take a further look at building it this way.