Homebrew 850 MHz filter.

Status
Not open for further replies.

Andy3

Member
Joined
Jul 17, 2010
Messages
78
Location
Cheshire, England
A new phone mast was erected just down the road recently, and now they've turned the darned thing on. One of my interests is eavesdropping on what people are doing with their wireless mics, headphones and other low-power links in the UK allocation around 860 MHz, but my AR-DV1 receiver is not pleased by the new BIG signals on ~950 MHz!
So I decided to build a band-pass filter. With the aid of my Signal Hound spectrum analyser and tracking generator I but this. It's a coupled bandpass pair, and the degree of coupling was adjusted by altering the central screen between the sections.
It works great, putting plenty of attenuation in above and below the wanted band and only a 6 dB in-band loss, which could probably be reduced further with a bit of effort.
The two L's are just about 1 inch of thick copper wire. The ground ends are pushed through holes in the double-sided pcb and soldered both sides. The ground legs of the trimmers (10pF) are also soldered both sides, as are the F-conectors. There are copper foil straps to the tinplate box. Tap points for the in/out connections are about 1/3 of the way up from ground.
 

Attachments

jonwienke

More Info Coming Soon!
Premium Subscriber
Joined
Jul 18, 2014
Messages
13,023
Location
VA
So the minimum insertion loss is over 6dB?
 

RFI-EMI-GUY

Member
Joined
Dec 22, 2013
Messages
4,318
Increase coupling = decreased insertion loss = wider bandwidth.

Sent from my SM-T350 using Tapatalk
 

Andy3

Member
Joined
Jul 17, 2010
Messages
78
Location
Cheshire, England
Yes, the analyser was normalised to take account of the connectors etc before sweeping the filter. The 6dB was a compromise really, it's not much to lose in this application as the signals are not weak. The main aim was to get a narrow-ish response and steep shoulders. It does the trick.
 
Status
Not open for further replies.
Top