[amsat-bb] Shoppinglist (Making a T notch filter)

Fri Mar 15 16:46:23 UTC 2019

How about rolling your own?

https://qrznow.com/145-mhz-low-loss-bandpass-helical-filter/

https://www.arrl.org/files/file/Technology/Intermod/No_Tune_Filter.pdf

Or DCI?
http://dci.ca/
⁣___
⁣Sent from my two way wrist watch
⁣⁣73 de W3AB/GEOOn Mar 15, 2019, at 07:39, Hans BX2ABT <⁣⁣⁣hans.bx2abt at msa.hinet.net⁣> wrote:

⁣Hello all,

⁣Unfortunately it's not one transmitter, but four of them (I thought 5, 
⁣but I just checked. Powers range from 1 - 10 kW), producing a lot of 
⁣spurious signals and raising the noise floor by about 10 dB when 
⁣pointing the beam into that direction. I don't think stubs will be broad 
⁣enough to cover 89 to 106 MHz, but I never worked with them, so I'm 
⁣guessing here. I don't have any problems with FM stations leaking onto 
⁣70 cm, just the air band, NOAA frequencies and 2 meters. My Airspy mini 
⁣also picks up lots of spurious signals  below 50 MHz, often hard enough 
⁣to ID.

⁣I found this filter from Par Electronics 
⁣(⁣http://www.parelectronics.com/fm-broadcast.php⁣), but it doesn't 
⁣indicate if you can tx through it. Otherwise I will have to use it in 
⁣the shack and remove it when I want to tx on 2m, with the risk of 
⁣forgetting it and blowing it up. Will a sequencer be a solution then?

⁣73 de Hans

⁣BX2ABT

⁣On 03/15/2019 09:42 PM, Robert Bruninga wrote:

⁣And you can make it without all the connectors at the T if you want.
⁣Though it takes some close and inventive soldering of the "T". Since the
⁣FM band is 88 to 108 that (I think) is far enough from 145 to add minimum
⁣loss. But at UHF, one needs to carefully check to make sure that the FM
⁣frequency is not also a multiple of the FM frequency.

⁣Tell us the FM broadcast frequency and we can take a quick look.

⁣Bob

⁣-----Original Message-----
⁣From: AMSAT-BB <amsat-bb-bounces at amsat.org> On Behalf Of Wendy and Terry
⁣Osborne
⁣Sent: Thursday, March 14, 2019 11:50 PM
⁣To: amsat-bb at amsat.org; Hans BX2ABT <hans.bx2abt at msa.hinet.net>
⁣Subject: Re: [amsat-bb] Shoppinglist

⁣Hi Hans,

⁣If you have a plenty of RG213 and suitable connectors, you could try
⁣making a Coax stub filter.
⁣You need a cable length that is an odd multiple of a quarter wave length
⁣long at the FM Tx frequency and an even multiple of a quarter wave at the
⁣frequency that you want (2M /70CMs).
⁣A single RG213 stub would have about 25dB of rejection and would pass 100
⁣Watts OK.
⁣You just need a coax T connector and some matching connectors.
⁣To trim the stub, use a set of garden secateurs.
⁣If you have a Bao feng or similar radio you could use that on the FM band
⁣attached to your T and trim the stub for minimum signal on the unwanted Tx

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