Thursday, September 22, 2011

902 Mhz Testing

Well today was burger Thursday, the "EAV" brought me a small package, if you could have seen
us in the parking lot of the joint you would have thought we were dealing drugs. hihi!
Anyhow here is the first of some many blogs to come to exploit better repeater receiver selectivity and sensitivity.
Tonight I solderd up the small packages into modules.
The next thing is to install them into the test radio and do some measurements with and without our test preamp that "XM" got for the group and ultimatly install this in the main receiver at commerce after we test and perfect it.
I tried the bandpass filter and preamp set up, it worked better but not as good as I would have liked,
Then EAV and I saw this ad on Ebay:
Recently found a source of small, inexpensive, muRata 2-pole 915 MHZ SMT bandpass filters. They appear to be adaptable for fabrication of 4-pole filters as used in the TK-931, etc. I am not selling these filters myself. If you contact me off list I will provide you with seller info. Basic filter performance is as follows:
Center Frequency: 915MHz
Bandwidth: 26MHz (902MHz to 928MHz)
Insertion Loss: 2.6dB
Ripple in BW: 1.0dB
VSWR in BW: 1:2.0
Rejection: -17dB min.
Number of Pole: 2
Surface Mount
E-Bay Item 160649985396.  At 10 filters to a lot for $3.99/lot + shipping
" EAV " got a 100 of em and shared 10 of em with me for testing and evaluation.
I chatted with Alex from the KW902 site about the filters & he also thinks they have decent potential.
There is also some potential for using these filters to fabricate a 6-pole filter (in a 2-pole by 4-pole configuration) for use in the TK-941 and TK-981 (in place of the existing pair of 3-pole filters).  
They might even work in a Maxtrac.  
Now comes the bench/field testing.
The tech info for the other 4-pole filters still in production indicates insertion loss on the order of 4.6 dB so 5 dB from a pair of these should be acceptable.
I’m thinking that replacing the original 938 MHZ filters with these will effectively be a nearly zero dB change in insertion losses offset by better 902-927 MHZ reception.
Investigating the actual performance of the radio with the new filters is going to be the telling issue.
I just hope it is better than the band-pass filter only arrangement we use now. 
All for now

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