Band pass filter for 50mhz

[Jesset1996.5]

I am working on a band pass filter for my 6m repeater of which does not use duplexes due to there large size and cost, It uses antenna spacing instead.
The antennas are just far enough for it to work but i need to reduce the db of the adjacent channel on the receiver a little. I have found a filter design that should work but i am a little stumped on the values of the capacitors. It says that they are polarized but i know for a fact that polarized caps do not go into the pf or nf range. Couldn't i just use a variable cap and a fixed cap together to make it somewhat adjustable?
I am new to RF circuits so any help is appreciated.   
the specs are as follows
Part Values
Part      Bessel
L1      0.0017 uH
C1      5370 pF
L2      38.61 uH
C2      0.2417 pF
L3      0.0003 uH
C3      35068 pF
 

[rhb]

Download Elsie from:

www.tonnesoftware.com/elsie.html

[ThomasDK]

Those component values look weird.
Normally the inductors would be 1000 times higher in value, and the capacitors 1000 times smaller.

0.0003uH = 0.3nH. A typical capacitor has more inductance than that... 

[Jesset1996.5]

Those component values look weird.
Normally the inductors would be 1000 times higher in value, and the capacitors 1000 times smaller.

0.0003uH = 0.3nH. A typical capacitor has more inductance than that... 

Exactly my thoughts, i can get the parts but im curious if there is another design that will work similar and have common value parts.

[KJDS]

If it's 50 ohms in and out then the filter should be symmetrical.

As it isn't, then either Elsie is unreliable or else you've set some impedances incorrectly

[matseng]

It says that they are polarized but i know for a fact that polarized caps do not go into the pf or nf range.

From what I learned the cap with one half as an arc (instead of just two straight lines) are just the US version of a regular non-polarized capacitor. Normally the polarized caps either have a + sign marking the positive side, or a hollow rectangle as the positive side line.

[rhb]

Attached are plots from Elsie.  I'll leave further work to the OP.

[dmills]

The OP may well do better to do something with a shorted 1/4 wave stub made of something seriously low loss, say a bit of LDF450 or something.

This generally makes a better notch then an LC network at those sorts of frequencies without having quite the beer barrel sized inconvenience of a cavity.

73 Dan.

[denverpilot]

... without having quite the beer barrel sized inconvenience of a cavity.

Typical 6m cavities aren’t anywhere near “beer barrel” sized. You don’t need that high a Q with the transmitter and receiver as far apart as most 6m repeaters are.

Ours are about 6’ TALL but they’re not that big around.

There’s a number of DIY 6m cavity designs out there, but I’m with you or whoever said it, just add a T and cut a quarter wave shorted coax line and use it as a notch.

The only downside is if you’re located at a very RF “hot” site, then you usually don’t want a coax notch filter acting as a receiving antenna and helping mix products in your transmitter. That will not make you any friends on a tower site.