I am 902 Mhz Playing Again

It has been a bit since I last posted, I am baby sitting some Painters and Sheet Rockers as they continue to remodel the office areas of my work place.

Yes that is Paint Fog , the flash caught it in the air.

Sheet rockers have been here! - This will be our product display area.

So I thought I would do a bit of 902 Mhz playing as well.

Today I am testing the rx VCO lock range of a stock Kenwood TK-981 that has had the front end filters changed out to a set centered in the 902-928 Mhz ISM band where we as HAMs have a allocation to transmit & receive at for our scientific, educational & hobby use.

These filters are used to keep unwanted out-of-band RF junk out of our radios and to make them more sensitve to the desired part of the band ie 902-928 Mhz, originally they were center on the 936 mhz part of the commercial part of the LMR band, 929-960 Mhz areas.

As you can see removing and replacing these filters is no EZ task.
It is all surface mount components, all which take time and patience to do and of course the right tools.

This particular radio's VCO got flakey about 924.2625 Mhz , so I need to adjust the VCO voltages and see if I can bring it down in frequency some more. The goal is to get full band coverage 902-928 Mhz on the receiver.

  

All for Now

Comments Are Always Invited

Sm0ke

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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 

SmØke

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

Sm0ke