# Comparator block? **URL:** \ **Category:** GNU Radio\ **Created:** [October 24, 2014, 10:16am UTC](https://www.ruby-forum.com/t/comparator-block/232728 "2014-10-24T10:16:28Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\ **Post date:** [October 24, 2014, 10:16am UTC](https://www.ruby-forum.com/t/comparator-block/232728/1 "2014-10-24T10:16:28Z")
Hi, I would like to have a comparator in my GRC block design to compair something like SNR or RMS or both on RX channels in my design. Logic would be something like… if channel A\>B then switch to channel B else use channel A. I have found the ‘slector’ block which looks useful in switching the channel sources based on routing value… I found threshold block which includes a comparator? but no comparator block. Is there a reason there is no comparator block? I read the IF statement should be avoided in FPGA design although a comparator is quite standard in electronic design ? Maybe there is a better way to achieve deversity and i’m missing something obvious? I want to have diversity switching in each differnt channel frequency / bandwidth and not just at the IQ source… any ideas much welcome… or even a pointer to a comparator block ! I’m new at GNUradio and have’nt made a custom block yet… but maybe its time to try !!! ?? ---
**Author:** ![brblakley](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/f14d63/32.png) [@brblakley](https://www.ruby-forum.com/u/brblakley)\ **Post date:** [October 26, 2014, 6:25am UTC](https://www.ruby-forum.com/t/comparator-block/232728/2 "2014-10-26T06:25:31Z")
Looking into this more it seams I will just have to add ‘IF else statement’ to generated python code.. It would be nice if GNUradio had this built in so I could experiment without hacking code!! Ah well, anyone know any reason why a comparator or an IF block was never included? Ben B. wrote in post #1160904: > Hi, > > I would like to have a comparator in my GRC block design to compair > something like SNR or RMS or both on RX channels in my design. > > Logic would be something like.. > > if channel A\>B then switch to channel B else use channel A. > > I have found the ‘slector’ block which looks useful in switching the > channel sources based on routing value.. > > I found threshold block which includes a comparator? but no comparator > block. > > Is there a reason there is no comparator block? I read the IF statement > should be avoided in FPGA design although a comparator is quite standard > in electronic design ? > > Maybe there is a better way to achieve deversity and i’m missing > something obvious? I want to have diversity switching in each differnt > channel frequency / bandwidth and not just at the IQ source.. > > any ideas much welcome.. or even a pointer to a comparator block ! > > I’m new at GNUradio and have’nt made a custom block yet.. but maybe its > time to try !!! ?? ---
**Author:** ![brblakley](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/f14d63/32.png) [@brblakley](https://www.ruby-forum.com/u/brblakley)\ **Post date:** [October 28, 2014, 5:56pm UTC](https://www.ruby-forum.com/t/comparator-block/232728/3 "2014-10-28T17:56:26Z")
Just in case anyone is interested ! I managed to get diversity switching between 2 channels with 2 RMS blocks with Probe of ‘VALUE’ in the RMS blocks. then used 2 Threshold blocks. Threshold block 1 with RMS\_Value2\>RMS\_Value1 as the the low and high threshold value. this passes a 0 or 1 to a variable that is used in the SELECTOR block to route the 2 SOURCE SINC BLOCKS on to demod etc… Anyway, Its a very long way around just using a comparator ( if RMS1\>RMS2 router= XXX !!! ) well, maybe that will make sense to somebody one day ! So far I have’nt managed to add the line directly into .PY code to make this work. I’ll post it here if I get it to work in a more graceful way. Or if I eventually get around to making a comparator block. Sidenote: the strem switches but theres an audiable crunch on the channel change after a few ms delay… tried switching audio and complex source ( same crunch noise ! ) Maybe I need a fast auto - pan on the audio channels to make a smoother switch!! Tried same SDR source block as input in case they were running out of phase / sync… same crunch noise… Perhaps the selector block is a bit clunky ! ?? will look into other ways of dynamic stream routing… perhaps I can code this in python in the stream routing section. will update here if I get anywhere with that