RF module for audio transmission - Page 1
Forum section: electronics / projects

author: msr
author_rank: Regular Contributor
timestamp: June 29, 2015, 09:32:01 am
content: Hi,Can you recommend me a cheap RF module with minimum range (LOS) of 1km and capable of transmitting (low quality) audio (preferably in real-time).The idea is to implement a kind-of walkie talkie.Thanks!

author: retrolefty
author_rank: Super Contributor
timestamp: June 29, 2015, 12:37:59 pm
content: Quote from: msr on June 29, 2015, 09:32:01 amCommercial or one off self use?Licensed or non-licensed in your country?Without knowing your legal options it's hard to recommend a frequency, antenna requirement, and power level required to meet a specific LOS specification.

author: msr
author_rank: Regular Contributor
timestamp: June 29, 2015, 01:23:16 pm
content: Ok, thanks for the questions!Licensed, worldwide preferably. (433MHz?)Not sure about power level but it would be nice no have a PCB/chip antenna in one terminal and a bigger one on the other one.The purpose of the system is to be used during sports classes, so the practitioner can carry a light and non-obtrusive terminal, and the teacher could have the bigger one.

author: tonyarkles
author_rank: Regular Contributor
timestamp: June 30, 2015, 02:32:19 am
content: This may seem too obvious but... would a cellphone work?For other approaches, you're probably going to quickly run into power limitations for unlicensed bands. 1km is a decently long range to meet while also respecting power level limits.

author: BennVenn
author_rank: Regular Contributor
timestamp: June 30, 2015, 02:47:15 am
content: Aliexpress sells 433mhz RF modules with audio + serial data links. From 0.5Watt up to 5Watt modules. Was looking at a pair then found a cheap 40ch UHF walkie talkie pair for $20 which had the same module in them at an opp shop

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 30, 2015, 06:42:00 am
content: Would directional antennas work for your application? If so, that would help greatly reduce power requirements.

author: LDM
author_rank: Contributor
timestamp: June 30, 2015, 11:30:25 am
content: Does the fact that you are looking for an "RF module" mean that this is to be built into a product?

author: Alexei.Polkhanov
author_rank: Frequent Contributor
timestamp: July 01, 2015, 05:59:57 am
content: I you want something working then you can look for Chinese models branded as "Senao" - they work up to 5 km and can be anywhere from $50 to $300. Sometimes these are sold under "EnGenius" brand.

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: July 01, 2015, 11:00:35 am
content: If you can elevate the tx module and have a good quality FM receiver, you can get over 1km with 433 MHz UHF data modules.It was initially a challenge to get good audio but messing around with bias got good results.In some cases your range may be limited by other low power devices on the same frequency.433.92 MHz seems to be fairly popular. However you can vary the frequency slightly, which in conjunction with a NBFM receiver, may reduce interference.Here's a 7 part video series (and suburban range test) done earlier this year.

author: LaserSteve
author_rank: Super Contributor
timestamp: July 01, 2015, 02:27:24 pm
content: Remember 433.950 is not for continuous wave transmission without a amateur radio license.Part 15 / license free devices on 390 and 430 Mhz have a limited duty cycle world wide. Unless you like the idea of jamming key fobs for cars.As my car depends on a rolling code locking strategy, I'd prefer not to be jammed, please.Steve

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: July 01, 2015, 07:48:59 pm
content: Quote from: LaserSteve on July 01, 2015, 02:27:24 pmPart 15 is an FCC rule relevant to the USA but different countries have different rules.In some countries these items are referred to as short range devices.In Australia the relevant document is the Low Interference Potential Devices Class Licence.Amateurs don't like them due to interference with 70cm repeaters, but our LIPD rules appear to have fewer restrictions than the equivalent in some other countries.Read up on the relevant document for your country as they may vary from the FCC rules.

author: Kalvin
author_rank: Super Contributor
timestamp: July 01, 2015, 08:15:37 pm
content: How about some walkie talkie modules? They should be free from continous transmission limits.

author: jeroen79
author_rank: Frequent Contributor
timestamp: July 01, 2015, 10:59:59 pm
content: Quote from: msr on June 29, 2015, 09:32:01 amWhy not get an off the shelf walkie talkie?You can get 466 MHz units with 8 channels.https://en.wikipedia.org/wiki/PMR446You could also look around for radio's used by motorcycle schools.These do what you described:QuoteCan you elaborate?What kind of sport(s)?What is the maximum size and weight for the sporter's receiver?Why would the instructor have a bigger terminal?A 466 MHz walkie talkie can be worn on a belt (or elsewhere on the body) with an earplug in the sporter's ear.Same for the instructor except he may need a push to talk button as well.Do you want to develope this so that you can sell it as a new product?Or do you want something to use in a local sportsclub?

author: msr
author_rank: Regular Contributor
timestamp: July 20, 2015, 03:49:33 pm
content: Quote from: jeroen79 on July 01, 2015, 10:59:59 pmWatersports (bodyboard, surf...).Maximum size and weight: something that can be placed inside an helmet and not too heavy so that it's still comfortable to use.This is something to use in a local sportsclub.Im currently having bodyboarding classes and we need to get out of water, after catching waves, to receive instructions from the teacher. That would be nice to avoid that specially when there are rip currents and it's hard to get in again