Testing 1000W 88-108MHz 9 Pole Low Pass Filter

[BriansBrain]

I received one of these - From ebay @ 23.10 EUR
0-1000W 88-108MHz 9 pole Pole Low Pass Filter

LPF.jpg

Insertion Loss Test
Siglent tracking generator connected to LPF in - and Siglent RF in connected to LPF out

Siglent - LPF - Insertion Loss.jpg

Return Loss Test ( if I'm doing it correct that is ? )

LPF - Return Loss.jpg

Siglent - LPF - Return Loss.jpg

[BriansBrain]

The two little spikes in the last Spectrum Analyser picture are Brian @ 96.8 MHz
and the local legal station SER @ 99.6 MHz from 100m up the road with 4KW pointing directly at my studio / workshop

[Marcel]

What are the value of the coils and capacitors on the pcb?
I want to recreate this filter and test it on an RF network analyzer.

I publish the data found here on the site in about 2 weeks.

[nrgkits.nz]

The capacitors looks to be ATC capacitors - rated for high voltages in RF allocations, they will all be 27p, with the pairs in center adding to 54p. The wire will be copper enamel probably in the order of 12SWG thickness.

It’s hard to tell from the photo, have they copped away the ground plane under the wire inductors? If not, then the Q will be less resulting in slightly degraded performance. I always chop away the ground plane under the inductors on my LPF’s and raise them off the board a little.

[radium98]

pcb size please .thanks @BriansBrain.It reminds me a copy of elenos LPF.

[BriansBrain]

pcb size please .thanks @BriansBrain.It reminds me a copy of elenos LPF.

Board size: 135mm x 50mm

Board Size 135x50.jpg

What are the value of the coils and capacitors on the pcb?

Here you go - the best I can do
Note all coils are the same.

C1 to C5.jpg

Coils.jpg

It’s hard to tell from the photo, have they copped away the ground plane under the wire inductors?

Under the coils on the top of the board there is no Ground Plane.
The bottom of the board has a 100% Ground Plane.

Ground Plane.jpg

[Marcel]

Mauri sells almost the same emty PCB from the dutch RF shop.

Most of the time what is offered on internet/ebay is not correct when you name it with a network analyzer and you have to make all kinds of adjustments to get it right.

My experience is that with a spectrum analyzer with tracking generator and vswr bridge you have a reasonable picture but not very precise and optimal.

Take a look at my previous posting.
I test a low pass filter with a vna and also give some building advice to get it good.

Regards,
Marcel

DSC_4065.JPG

[Marcel]

Here you see both the pass (yellow, magnitude) and reflection (blue, SWR format) at once.

You can only achieve this AFTER adjustment.

Schedules on the internet and those building kits is nice but you have no idea if it actually good because of the construction tolerances.

I don't want to discourage anyone but this is my experience.

[rigmo]

[Marcel]

I looked on the site of the best man but I am nor really impressed with the constuction of the whole.
Not the right capacitors and wires that are too long.
Between the coils no shield and too low in the housing (lower Q factor).

I have added a picture of the harmonics suppression of the simpler filter described by me (jusy search between my posts here on the forum)
As you can see, -80dB is achievable (BLF 278 300 Watt homebrew FM transmitter) if you follow my simple tips.

[rigmo]