Monday, November 21, 2011

Utah Radio: Maxtroller and Maxduino

Utah Radio: Maxtroller and Maxduino: After learning about the Arduino microcontroller and hearing how it had been used to turn an old Motorola Maxtrac radio into a trunk...

Friday, November 4, 2011

This & That on 902 Mhz

From a friendly out in the Interwebs..

Hi Bob,

I just checked your blog to see how you were progressing on your TK-981 receiver testing with the mini-filters in place.  It looks like you are also captured by other events.  I’m still battling my signal generator so I haven’t gotten down to cases with my TK-981 testing either.

Good luck with the repeater efforts,
Skip Clark, WB6TXX

Well Skip I have been testing those filters of yours and they work! :)

Jeremy -KD0EAV has ordered some more of those little critters I believe for some of our winter bench projects.

The initial RX testing was done on a TK-980 modded to RX at 902 Mhz.

The band went from being usable on one or two channels to being usable on many more & our noise floor went from -115 to -110 dbm  to -125 to -130 dbm on average. 
Basically, on the worst channles we dropped the noise about 15 db. 
It made a big difference in the front end performance of the 902 RX side of the repeater. 
And of course we have a +15dbm Chip Angle Preamp & Band-pass filter helps with some of the insertion loss we get from all the filtering we have added with no increase in the noise floor.

More a bit later....

All For Now 
Comments invited 


Sunday, October 30, 2011

Saturday Booth Site Work

Reworked the receiver pre-amp into a more rack friendly mounting.

Replaced the power supplies and HSO/ controller cards for the nucII
back into rack.

Moved the modified receiver to the 902.0125 freq. from the test channel

Reset network equipment after it was off for 3 days.
(bad cable in rick not sure which one) hopefully it will stay on now.

Installed the 444.975 machine back in rack since it got the boot
over at Lee's Summit still need to retune it back to 444.975
As I had it on a different freq over there. No 444.975 just yet but it
is mounted in the rack :)....

Still trying to find out why I still have sq tail on the 902 rx here,
have added dc blocking cap . I may need to check usb DSP filter / gain settings.

Making plans to get over to the KcKs downtown site to retrive the receiver for rx modding and filter upgrades.

All for now


Friday, September 23, 2011

More 902 Mhz Fun

This picture pretty much says it all.
I installed the filter modules this morning just before work and snapped pics of them at lunch.

Here is some more pictures of the unit I am working on and a couple from the TK-981 rig I use at work showing the orignal 938 centered filters installed. the unit that is under test is a TK-980 rig we modded to use a 902 receiver.

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

Wednesday, September 21, 2011


Well moved the blog to a new location today.

Will move some of the older stuff over later.

All for now, comments always invited!


Me at the helm of KØRU's Ham Station in Gardner, Ks.