that guide is for those people who have tried to get "Transmission Received" but ended up having 1-2 radios left. with the instructions below you can find which radios you have missed

• download that file - https://drive.google.com/file/d/1DnpWbB13Rxc5A3xkzh2Sq9bmVYJ9nnwC
  
• open that file in a browser (it is a HTML file)
  
• follow the instructions to find which radio(s) you have missed
  
• return back to that guide for details and screenshots of the missed radio(s)

• follow that link - https://jsfiddle.net/xrudpnzg/
  
• follow the instructions on the bottom-right window to find which radio(s) you have missed
  
• return back to that guide for details and screenshots of the missed radio(s)

• game save your current achievements progress (including which radios from "Transmission Received" you have received a signal at) in the following file
  
  "...STEAM\steamapps\common\Portal\portal\gamestate.txt"
• each achievement (and its progress) is saved as a separate "id"; "Transmission Received" is under "id" : "149"
  
• the "data" value stores what radios you have successfully activated. that information stored as HEX (base-16) value and can be anything from "0x0000000000000000" (activated 0 radios) to "0x0000000003FFFFFF" (all 26 radios are activated)
  
• each digit of "data" (0 to F) stores information about four radios in BIN (base-2) format. for example "F" ("1111") means that you have found 4 radios, while "9" ("1001") means that you have missed second and third radio in that segment
  
• what I have done is to decipher which digit of "data" stores which radios, and wrote a script that can take any given "data", parse it, and report back which radio have been missed
  
• for example, if you paste the following data "0x0000000003B8A293", then script shall return that you have missed the following radios:
  
  #03 (chamber 02), #04 (chamber 03), #07 (chamber 06), #08 (chamber 07), #10 (chamber 09), #12 (chamber 11), #13 (chamber 12), #14 (chamber 13), #16 (chamber 15A), #18 (chamber 16), #19 (chamber 17), #20 (chamber 18A), #21 (chamber 18B)
• the map for "data" is (from left-to-right):
  
  1 digit: "#26 (escape 02)", "#24 (escape 00)" 2 digit: "#22 (chamber 18C)", "#21 (chamber 18B)", "#06 (chamber 05)", "#25 (escape 01)" 3 digit: "#23 (chamber 19)", "#20 (chamber 18A)", "#19 (chamber 17)", "#18 (chamber 16)" 4 digit: "#17 (chamber 15B)", "#16 (chamber 15A)", "#15 (chamber 14)", "#14 (chamber 13)" 5 digit: "#12 (chamber 11)", "#13 (chamber 12)", "#11 (chamber 10)", "#10 (chamber 09)" 6 digit: "#09 (chamber 08)", "#08 (chamber 07)", "#07 (chamber 06)", "#05 (chamber 04)" 7 digit: "#04 (chamber 03)", "#03 (chamber 02)", "#02 (chamber 01)", "#01 (chamber 00)"
• after you have learned which radios you have missed, use the table below for extra help

• if you need more screenshots and help, then check the guide by @lonerunner
  https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=213131869
  
• if you are absolutely sure that you have collected all radios but still didn't get the achievement, then you have a bugged progress; in that case follow the guide by @Calmly_Frenetic
  https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=419856706
  
• if you get tired of radio's music (upbeat salsa) and want to mute them off, then follow the guide by @Calmly_Frenetic
  https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=432359161

if you want to thank me...

...then check my guide about fixing various game issues: launching, crashing, optimization, stuttering, gamepads, etc. the guide is huge, but the topic is broad to begin with
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=1935376439