Field Day/Em-com coax stub filters
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- Опубліковано 25 чер 2015
- Coax Stubs. How to build and tune dual band coax stubs. based on the November 2004 "hands on Radio" QST article. Using just the MFJ Antenna Analyzer.
Link to Article
p1k.arrl.org/pubs_archive/105771 - Навчання та стиль
Thanks for posting the video. That was the best demo on how much they suppress and how to cut them. Thanks!
+cpg0000 Thank you. I had planned follow up field day vid with multi transmitters on site. I will this year. I am also going to build some 80 meter stubs
I have a Bird Low Pass filter that clips anything above ~430Mhz @ 60dB that is based on this same theory, It's just a bunch of Coax Stubs. This is the kind of neat stuff that it's good to see videos or write ups on.
Thanks, I know its an old vid, But I will soon have a mini VNA I want to learn. Then I can revisit this and actually measure the attenuation and width.
Nice video and great demo. It really shows how well stubs work. I liked the idea of the switch on the end for using the stub on numerous bands and not having to remove it when you change bands. Well done.
Barry, KU3X
Very, very good first video.
Shows you have latent talent to produce technical vids. Please post more of your HAM expertise.
BTW: Rather useful info for multi txfr opps. Thanks....
Very cool! Build one of these ASAP!
great job on your first Vid
Nice job. Very helpful.
Thanks
Nice Video. Good info DE 4S7AB
Very good job
Thanks
Good Job. You mention low power applications, does 100 watts fall in this category? recommended switch rating?
Thanks! 73
Sorry for the late reply. Yes 100 watts is what I have used. I have not tried more power
Hi. Where do you place the Tee for the stub? At any 1/2 wavelength along the feedline? Does this also help to filter other unwanted noise? Or only unwanted noise that also appears from the harmonic frequencies?
I placed it just a couple feet from the rig with good results, I have not tried any other placements. It will help on other noise, if the noise originates out of band. Harmonic suppression is in the mid to high 20s DB depending on the coax used. The next step is band pass filters that have three times more attenuation. I use both. After this vid was made I got a 20m and 40m filters. These are much better and much more expensive. Using the stubs with the filters makes it even better.
I'm just now starting to learn about stubbs and wondering if you could answer question is it a true statement that anytime you connect a stub to a T connector it is considered to be in parallel?
Yes, In this application. There are stubs used as matching sections for antenna tuning that are used in series.
so how would this work as a filter to stop UHF ??
as in a repeater i want to RX 433.000 but want to stop 439,000
would this be possible ??
measure coax and trim back until x is zero on 439.000 ??
It might work but I don’t know how wide the notch would be. 433 and 439 are not harmonics of each other.. Most repeater builders would use a crystal filter for that.
You would need to use a low loss coax at UHF. LMR 400 or 600. It would be a good experiment that would not cost much. a quarter wave at 433 is not much coax
@@amrwhiskey3456 could you add two stubs tuned either side of the desired frequency to filter it better? Perhaps also variable capacitors so the stubs are easily tunable?
@@izzzzzz6 the stubs are not sharp enough for that, they cover most of the band. But you can add more stubs for better attenuation.
How wide is the curve?
It covers most of the band, It is too wide for use as in band notch filters. Like operating CW and SSB on the same band. I don't have a vna or spectrum analyzer to measure one. But others online have done it, I may have a vna soon.
How do you tune coax
Since the impedance repeats every half wave ,you can measure the electrical length with an antenna analyzer. so you trim (tune) the length by the impedance or reactance measurements.
here is a link to the article if your an ARRL member
p1k.arrl.org/pubs_archive/105771
235
Thanks for the sub