Topics

EVO Filter construction


John Fell
 

"Evanescent filters are so easy to throw together, and drilling too many tapped holes while just playing around .... ".

This from Mr "I don't do mechanical things "   LOL.

As Andy says WG16 does work well @ 13cm but needs some care as the setting screw to guide wall is very close .I too have made a few - Tip - add wingnuts and locknuts - it makes adjusting a lot easier .You do not need to close the guide ends , but if you do to keep insects etc out of the filter ,use adhesive backed copper tape .

73
John
G0API


Andy G4JNT
 

WG16 at 9cm, not 13
Do like the wind nut idea

Drilling holes and tapping is about the limit of my metalworking skills



On Sat, 30 Jan 2021 at 10:30, John Fell <john.g0api@...> wrote:
"Evanescent filters are so easy to throw together, and drilling too many tapped holes while just playing around .... ".

This from Mr "I don't do mechanical things "   LOL.

As Andy says WG16 does work well @ 13cm but needs some care as the setting screw to guide wall is very close .I too have made a few - Tip - add wingnuts and locknuts - it makes adjusting a lot easier .You do not need to close the guide ends , but if you do to keep insects etc out of the filter ,use adhesive backed copper tape .

73
John
G0API


Mark GM4ISM
 

I haven't looked yet for WG15, I probably have some short bits

I have reasonable amounts of WG14 though, if anyone wants some.

Mark GM4ISM


On 30/01/2021 10:30, John Fell wrote:
"Evanescent filters are so easy to throw together, and drilling too many tapped holes while just playing around .... ".

This from Mr "I don't do mechanical things "   LOL.

As Andy says WG16 does work well @ 13cm but needs some care as the setting screw to guide wall is very close .I too have made a few - Tip - add wingnuts and locknuts - it makes adjusting a lot easier .You do not need to close the guide ends , but if you do to keep insects etc out of the filter ,use adhesive backed copper tape .

73
John
G0API

Virus-free. www.avg.com


Neil Smith G4DBN
 

After Andy mentioned this type of filter some time last year, I had a go at making some. Because of my metalbashing addition and for general bling (and maybe performance), I made the tuning screws from Tellurium Copper, with knurled heads for easy finger-tweaking.  I might still have a few of the tuning screws kicking about if anyone wants some to try.  I cut the threads deliberately oversize to improve the fit, and made slightly thicker than standard brass locknuts, although the pic shows a stainless one.  I also made up some solder-in threaded collars to give a longer thread engagement, but that is more faff than just drilling and tapping the holes.  I used a thread-rolling tap rather than a normal cutting tap for the copper waveguide.  Whether they work any better than brass screws, I didn't have the energy left to investigate, but I had a pile of machine-shop fun, and that's an end in itself. These are M3 x 0.5 with 9mm head and 2.3mm plain shaft.  I also did some M4/M5 and giant ones which were extra-fine M8 x 0.5 threads and some teensy ones with M2 x 0.35 threads.  BA would actually be a better choice because of the thread angle, but I don't own any BA taps/dies.  Using a tapered split collet worked OK at 4mm, but it was getting tricky at smaller diameters.  It was a fun way to idle away some time on a summer afternoon.

Neil G4DBN



On Sat, 30 Jan 2021 at 10:30, John Fell <john.g0api@...> wrote:
"Evanescent filters are so easy to throw together, and drilling too many tapped holes while just playing around .... ".

This from Mr "I don't do mechanical things "   LOL.



Paul G8AQA
 

Very sad you don't have any BA taps and dies. I have 0BA to at least 12BA with nuts and screws to suit.
🙁
Paul G8AQA

On 30/01/2021 16:27, Neil Smith G4DBN wrote:

After Andy mentioned this type of filter some time last year, I had a go at making some. Because of my metalbashing addition and for general bling (and maybe performance), I made the tuning screws from Tellurium Copper, with knurled heads for easy finger-tweaking.  I might still have a few of the tuning screws kicking about if anyone wants some to try.  I cut the threads deliberately oversize to improve the fit, and made slightly thicker than standard brass locknuts, although the pic shows a stainless one.  I also made up some solder-in threaded collars to give a longer thread engagement, but that is more faff than just drilling and tapping the holes.  I used a thread-rolling tap rather than a normal cutting tap for the copper waveguide.  Whether they work any better than brass screws, I didn't have the energy left to investigate, but I had a pile of machine-shop fun, and that's an end in itself. These are M3 x 0.5 with 9mm head and 2.3mm plain shaft.  I also did some M4/M5 and giant ones which were extra-fine M8 x 0.5 threads and some teensy ones with M2 x 0.35 threads.  BA would actually be a better choice because of the thread angle, but I don't own any BA taps/dies.  Using a tapered split collet worked OK at 4mm, but it was getting tricky at smaller diameters.  It was a fun way to idle away some time on a summer afternoon.

Neil G4DBN



On Sat, 30 Jan 2021 at 10:30, John Fell <john.g0api@...> wrote:
"Evanescent filters are so easy to throw together, and drilling too many tapped holes while just playing around .... ".

This from Mr "I don't do mechanical things "   LOL.




Virus-free. www.avg.com


g4cch_1
 

I have taps for: 0, 2, 4 , 6 and 8BA
Will probably use 2 or 0BA brass screws and nuts on my next filter attempt.

Just waiting for WG14 now.

Will scale dims from Andy G4JNT's 3.4GHz article, based on ratio of waveguide dimensions. 

If this is not the way to do it, then please let me know...

Thanks and 73
Howard,  G4CCH 


Andy G4JNT
 

I looked at the values yesterday, and scaling WG16 for 3.4 to WG14 for 2.3 is pretty close.
You do end up with quite a large clump of metal though.  That original 3.4GHz design had 60Mhz bandwidth, and at 2.3Ghz that scales to 40MHz, so you could afford to shorten the spacing of the tuning screws to widen the BW a bit.

If you come up with a good workable solution and response, write it up.  
I think I've got some WG14 somewhere in the shed, and if it's long enough may try a breadboard filter too.  



On Sun, 31 Jan 2021 at 09:32, g4cch_1 <g4cch_1@...> wrote:
I have taps for: 0, 2, 4 , 6 and 8BA
Will probably use 2 or 0BA brass screws and nuts on my next filter attempt.

Just waiting for WG14 now.

Will scale dims from Andy G4JNT's 3.4GHz article, based on ratio of waveguide dimensions. 

If this is not the way to do it, then please let me know...

Thanks and 73
Howard,  G4CCH 


g4cch_1
 

Thanks Andy, will report what it performs like,  and if OK, I will write it up

Howard, G4CCH 


Andy G4JNT
 

The difficult bit I found was the input / output coupling, in other words the transformers.   They have considerable effect on the ripple, and all you can really do is just play around until it's acceptable (or good :-)

That original 3.4GHz design I spent a lot of time on, having unfettered access to an microwave Netan at work back then, hence the experimentation and determination of that tongue-in-cheek equation.   It's a pity that with all the low cost netans one the market now, all are only any good for UHF and down.   There's still little around to use for matching at microwaves.    A directional coupler, swept or wideband source  and power detector or, better, a tracking generator and SpecAn is the best many can manage at home now.




On Sun, 31 Jan 2021 at 10:00, g4cch_1 <g4cch_1@...> wrote:
Thanks Andy, will report what it performs like,  and if OK, I will write it up

Howard, G4CCH 


John Fell
 

Tracy Tools do the full range of BA Taps at modest cost and rapid delivery .BA are better contact RF wise they say .

If you have a SA and no tracking genny I found that using Andy's design of Sat mixer diode harmonic generator , fed by an old LAR Antenna bridge at around 100MHz , makes for a lovely flat broadband noise source .Bosh on a mod amp and it will provide service to well beyond 10GHz .

I have used 2BA brass studding , cut to length and end drilled to fit SMA socket spills , soldered on , to provide the coupling transformers .

The EVO is very forgiving in construction terms - if thru loss is not important ,such as bandwidth /passband duty .Skirt rolloff is reasonably fast with a 3 pole design .

73
JOhn

G0API

On Sun, 31 Jan 2021 at 10:10, Andy G4JNT <andy.g4jnt@...> wrote:
The difficult bit I found was the input / output coupling, in other words the transformers.   They have considerable effect on the ripple, and all you can really do is just play around until it's acceptable (or good :-)

That original 3.4GHz design I spent a lot of time on, having unfettered access to an microwave Netan at work back then, hence the experimentation and determination of that tongue-in-cheek equation.   It's a pity that with all the low cost netans one the market now, all are only any good for UHF and down.   There's still little around to use for matching at microwaves.    A directional coupler, swept or wideband source  and power detector or, better, a tracking generator and SpecAn is the best many can manage at home now.




On Sun, 31 Jan 2021 at 10:00, g4cch_1 <g4cch_1@...> wrote:
Thanks Andy, will report what it performs like,  and if OK, I will write it up

Howard, G4CCH 


Andy G4JNT
 

Well, a chap in the Filter Group at Matra Marconi Space (as was) once said so. 

On Sun, 31 Jan 2021 at 10:38, John Fell <john.g0api@...> wrote:
... BA are better contact RF wise they say .