I recently got myself a new toy...

[BriansBrain]

Brian, the best way to tune a filter is to look at the return loss rather than the insertion loss, which seems backwards.
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If I only had a SA and TG, I'd get it lined up with the return loss then check it for sanity by measuring insertion loss, tweak as necessary and repeat.
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Yes, you could use the reflected port on the directional coupler but at 60 dB coupling factor (as on the one you posted a picture of) you're going to run out of dynamic range using a spectrum analyser and tracking generator.
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A 30 dB directional coupler would probably suit you best.

OK...
So I need a 30dB coupler with both test ports Reflected and Incident (Forward) for this test

From 80 > 400MHz ?

[BriansBrain]

Your sampler looks OK.

Thanks

I still think that SO239s are best used for CB! I stopped using them way back

Trouble is all my stuff now is 239's it would take me hours to replace them all

I wil have to think about it

[BriansBrain]

Try spreading them out with a ceramic screwdriver if you've got one whilst having it connected to the spectrum analyser and tracking generator.
If you do it with your fingers you'll find that the trace moves a certain way when you touch it, potentially more than the adjustment you're making, so when you let go it has gone even worse even thought it looked better when you were touching it and moving it. A potentiometer "twiddler" can also work.

OK... I understand this adjustment and what to look for on the SA

As I said in my previous post, being able to see return loss will help you but only after a lot of practice, it's not very intuitive, especially using the return loss method. It can be frustrating if you're starting out. I doubt many will admit it.

This "return loss" test I don't understand + I don't know what or how to look for it

You want to bring those peaks at markers 3 and 4 down as low as possible, and have as little loss as possible in the pass band (around your carrier frequency). There's no reason why you shouldn't be able to get 0.2 dB in the pass band.

OK... now you are back to talking about the LPF normally connected to the spectrum analyser and tracking generator as in the first test I did in this thread.

On the second one you tested, with the blue loop of coax on the output of the transistor, be aware that the input to that filter might not be 50 Ohms. This is a completely different can of worms. I don't really like integrated filters for that reason - you can't tune them properly.

So how could I do a proper test of this LPF on that board

[BriansBrain]

Another important thing to bare in mind is to normalize the analyzer so you can as close to an accurate reading as possible. If you are measuring return loss you can normalize with an open load on the directional coupler - since no coupler is ever going to be perfect, and there will be differences in your cable, connectors and analyzer also. Normalizing attempts to "zero" out all of this so your DUT (device under test) is the only thing which will influence the end result you're looking for - not adding the losses in your cables, parasitic inductance's etc... and so on.

I am just getting to grips my my new toy

I have read about how and I understand the normalize function and I am playing with it

[BriansBrain]

OK
Speaking of LPF ... anyone tried one of these...
https://www.ebay.co.uk/sch/i.html?_from ... e&_sacat=0

ebay > Seach for > 0-1000W 88-108MHz 9 pole Low pass filter LPF for FM Broadcast transmitter

0-1000W 88-108MHz 9 pole Low pass filter LPF for FM Broadcast transmitter-S.jpg

[Bton-FM]

OK
Speaking of LPF ... anyone tried one of these...
https://www.ebay.co.uk/sch/i.html?_from ... e&_sacat=0

ebay > Seach for > 0-1000W 88-108MHz 9 pole Low pass filter LPF for FM Broadcast transmitter

0-1000W 88-108MHz 9 pole Low pass filter LPF for FM Broadcast transmitter-S.jpg

It is sold by 'unique electronics' the one that can't cut the hole for the fan right .....

[Bton-FM]

I'm looking for a 30db at a reasonable price ... any suggestions

You could build your own but probably won't have a good frequency response at UHF?

I had a go at making one of these RF-Power-Sampler which is the same thing ( or is it ? )
http://www.n4ga.com/50db-hf-rf-sampler/
RF-Power-Sampler Diag.JPG

My Attempt

RF-Power-Sampler - Mine.JPG

On Test =
RF-Power-Sampler - Mine - Siglent.jpg

As you can see it's OK over the FM band

Yes that's exactly the design I was talking about, I might have a go at building one of those since I recently got a new (old) (and really f***ing heavy) toy

If I do I'm going to use a different core material for the torroid.

Speaking of R.F samplers / directional couplers does anyone have any reccomendations?

[Marcel]

This is my Band 2 LPF up to 250 Watt RF.

Tips:

1: Wind all the coils on the same uncut wire.
2: Coils cannot "see" each other its necessary to install separtion walls.
3:<<SPACE>> between coils and walls.

L1, L2, L3: 4 turns 8 mm 1,5 mm wire
C1, C2, C3, C4, C5, C6: 27PF capacitors 500 V tube or ATC 100B

I have more than -72 dBC (all) harmonic suppression with a Broadband Band 2 BLF 177 amplifier.

[Marcel]

in band attenuation and vswr

[Marcel]

More than -90dB about 300 MHz with separation walls between the coils.

DSC_4077.JPG

[Marcel]

RF construction details for good results.

[BriansBrain]

This is my Band 2 LPF up to 250 Watt RF.

Cool LPF

I like the design

[Bton-FM]

RF construction details for good results.

what gauge wire do you use on your filters?

[Electronically]

RF construction details for good results.

what gauge wire do you use on your filters?

18swg

Sent from my AMN-LX9 using Tapatalk

[Bton-FM]

RF construction details for good results.

what gauge wire do you use on your filters?

18swg

Sent from my AMN-LX9 using Tapatalk

Thankyou

[rigmo]

0-1000W 88-108MHz 9 pole Low pass filter LPF for FM Broadcast transmitter-S.jpg

Be real wake up..
This LPF filter can handle up to 600W after that you put many thing on cube.... very good LPF

[rigmo]

Now...
I got one of these Chinese 0-1KW 88-108MHz Low pass filter a while ago and have never used it yet
ebay - Chinese - 0-1KW 88-108MHz Low Pass Filter.jpg

So I put it to the test, tracking generator to the board input and the output to the RF input
Both set to 50 Ohm.
Chinese - 0-1KW 88-108MHz Low Pass Filter- Under Test.jpg

This was the result, it does not look correct for a 88-108MHz Low Pass Filter
Chinese - 0-1KW 88-108MHz Low Pass Filter - Siglent.jpg

Am I doing something wrong or is the board not within spec ?

How many seconds 1kw haha this is peace of shit crape! wire max 300W but im not sure can handle even that !

[rigmo]

I don't mind stretched coils - it usually suggests that someone has actually tuned the damn filter! One common cock-up is to put the coil against the board (like in the picture above) destroying the Q of the coil, and causing high induced currents in the ground plane. I saw a (whisper it) Broadcast Warehouse PA that had suffered from a big current being induced into the ground plane, with the copper foil rippled and burnt and one of the filter caps had desoldered itself!

My Band II PAs usually have the output filters on separate boards, and the coils are around 8mm above their board, with the groundplane etched away under the coil. The improvement in Q is huge. All the coils are offset to prevent mutual coupling and the high voltage caps are flat to the PCB, but clear of the coil windings. When I next have one nearby, I'll put up a picture. The design was published in the 1960s in the ARRL handbook - they gave a really easily reproduced PCB layout that could be used on most of the VHF bands without modification.

Albert what sort of configuration are your filters? The ones I have constructed are usually a 9 pole chebyshev with 5x capacitors and 4x inductors. I usually use 16SWG tinned copper wire and pairs of 27p ATC100B capacitors for the inner poles (54p total), and single 27p caps for the 2x outer poles.

I also have another filter here which I bought second hand locally. It was used in a mobile RT installation in the A band below 88MHz for taxi's etc... its in a metal box and configured with 3x high voltage adjustable capacitors and 4x wire wound inductors using 18 SWG tinned copper wire. The rolloff was originally set at around 90MHz of thereabouts, but I widened the coils as much as I could and re-adusted the capacitors, now the roll off is a little above 108MHz, enough for a usable passband upto around 103MHz before there's too much attenuation.

lpf.jpg

Edit: Here's a filter I've spent this evening constructing and aligning, the analyzer trace is the insertion loss. I discovered my directional coupler had issues (Mini-Circuits ZFDC-20-4L) so had to resort to using my Diamond SX-200 SWR/Power Meter and a transmitter on 8 Watts into the filter to adjust for best return loss. In the end I had no measurable SWR/Reflected power on the meter and an insertion loss no worse than -15dB on the analyzer.

analyzer.jpeg

filter.jpeg

For calibrate LPF only with SA its to expensive toy... better use nanovnaF ! can tune antena LPF etc...
every cat-of over 130Mhz its nice... good LPF ! nice tune... ( 300w )

[rigmo]

s-l1600 (10).jpg

This one can handle 1kw above 1.2kw im not sure ...
https://www.ebay.com/itm/0-1500W-88-108 ... 2889911898

[rigmo]

only Bird 4275-020 Variable RF Sampler 20-1000MHz
or Mini Circuits ZFDC-20-400 1GHz 20dB Directional Coupler Type N