Coax Stub Filters

[@mikesradiorepair]

I use coax stub filters for amateur radio events like Field Day where there are several radio operators set up in close proximity to each other. A couple of tricks if you use stub filters for events like this. First, add a toggle switch to the end of the coax cable so you can change your stub filter from a open to a short. In use if you make a 1/4 wave 40 meter stub filter having the end of the stub shorted or open changes the bands that are filtered. In the case of the 40 meter stub either 20M and 10M or 40M and 15M. Another trick is to use a impedance trombone. This allows you to fine tune the overall cable length to precisely null out a frequency where you might be interfering with another operator. Mike KC3OSD

[@R2AUK]

👍 Another reason why such filters differ from the models are cable losses. RG58 has quite noticeable losses above 100 Mhz. (1+ dB per 5 meters).

[@Jaunis100]

RG213 better

[@justme-n-gracie]

excellent presentation!

[@layt01]

Very good as always. I think Smith charts would be a nice topic for many videos.

[@andrewmcfarland57]

Yes, i'm embarrased to admit that i have a mental block to understanding the Smith Chart. I too would love to finally slay my old nemesis. 🙂

[@anonymous.youtuber]

Nice ! One might use a coax trombone to play around with the length parameter.

[@Stefanev]

Thank you for new very useful lesson.

[@DiegoColl44]

Nice video !! Saludos desde Argentina

[@electronics.unmessed]

interesting lesson! 👍

[@ricardokers]

I discovered your channel a few days ago and I am enjoying your explanations; they are very comprehensive and very educational. Do you have any material on thyristors and their activation?

[@FesZElectronics]

Unfortunately not... I did not cover thyristors, diacs or triacs in the past. Maybe this is a good subject for the future.

[@ricardokers]

@@FesZElectronics Thank you, I would like to. I'm really liking the way you explain and the reasoning you use.

[@andrewmcfarland57]

RG58 ? I might use RG8 to latch the chicken coop,🙂 but considering how much modern radios cost, save up your money for some flavor of LMR-400 at the minium, especially for VHF. Thanks for laying out the theory for us.

[@mr1enrollment]

note: to those of us that are color blind - the green is almost invisible.

[@m1geo]

I made a coax stub filter for 144.3 MHz to stop 2m band inference on my TV. The 5rd harmonic took out the main BBC DVB transmission on 721.5 MHz in my area, so the plan failed! 😂

[@FesZElectronics]

This is quite a difficult problem with transmission line filters - you have multiple pass and stop bands... the most annoying thing is when you want these, and they are not exactly where they should be... I tried building a cavity filter for 145MHz, hoping it will also pass the 70cm band (145x3=435). However, the ratio was not exactly 3 but rather 2.9 or something, so that plan failed...

[@m1geo]

@@FesZElectronics That's a cool idea though! But it also explains why handheld antennas on 144 MHz aren't great on 432 MHz, as they usually rely on the same (tenuous) harmonic relationship.

[@m1geo]

@@FesZElectronics PS, thanks for the excellent content! Love the videos!

[@KratosGhostofSparta-pp1cr]

Sir could you please make a video on how tl431 works in feedback of isolated smps and how is compensate the system. thank you

[@mauricedemel6142]

Hello.Do you have good quality valve(Tube) Amplifiers.?