Monday, November 29, 2021

Doing "data stuff" over VHF/UHF FM?

First, let me set up a user scenario so this makes sense as to what problem is being solved.  

Imagine you are somewhere where you have a fully charged smartphone, but no network access of any kind along with a dual band handheld amateur radio.  

Aside from the above, you happen to have some type of HF radio with you, but you forgot a few important things at home like a Morse code keyer and some important thing that prevents you from powering your HF radio, like a power cord, fuse, etc. 

Your only method of outside field communications is with your handheld radio now! 

Luckily, you have a few extra things  with you such as an Easy Digi Interface and a USB-C to 3.5mm adapter with you. How can you communicate using non-voice modes?

Sending certain data signals over FM provides some benefit. Lets explore a few of these where you will be connecting your smartphone to your handheld radio.

Smartphone Headset Adapter

If you have a smartphone with a headphone jack, that is great but is feature becoming less common.

The latest Android or Apple devices have done away with the standard 3.5mm headphone jack and is why you need an adapter that goes from USB-C (Or Lightning) to a 3.5mm jack.

For $9.99, this USB to 3.55mm TRRS headphone adapter gadget can be yours and will find many other uses you can think about.  Support fellow Hudson Valley club OMARC by using Amazon Smile.

Easy Digi Interface

This simple box allows you to connect your smartphone to your handheld radio.  You may or may not need the smartphone headset adapter, but lets pretend you do.  

It is now simple for you to connect your radio and smartphone together thanks to KF5INZ and the appropriate version of his adapter for your radio. Below is pictured the version appropriate for the Alinco DJ-MD5XTG DMR radio along with the USB-C to 3.5mm TRRS adapter.

An alternative option, but still using a different form of the Easy Digi Interface was even written up by HVDN's Joe NE2Z back in 2019.

Do Not Leave Home Without Software

Since you do not have network access to download applications on your smartphone in this described scenario, install a few before you get stuck somewhere.  

The first application to focus on is one that you can send pictures with.  SSTV and its different modes offer different benefits and this ability might come in handy to increase situational capabilities.

The second application to focus on is something that can send text data in a conversational format.  Modes like RTTY and PSK31 are great for this as they work just fine being sent over FM.  Small or large amounts of text can be shared with these modes. VARA FM is not a focal point in this article since we are focusing on basic implementation for basic users.

A third application is something where you can share your location and short embedded messages.  APRS.  APRSdroid is a great way to start related to APRS without a dedicated APRS radio. 

Here is the list of essential communications applications you should have on an Android device relative only to the use case described in this article.

Please note that similar versions exist for Apple devices, but HVDN can not provide comment/support on those, but we welcome your Apple favorites. 

Robot36 - Highly Recommended as SSTV reception application because of modes supported like PD50.

SSTV Encoder - Recommended for SSTV transmission via supported modes like PD50

APRSdroid - Highly recommended for sound card based APRS with appropriate interface cable.

droidRTTY - Recommended for RTTY over FM or other modes.

droidPSK - Highly recommended for send/receive of PSK using appropriate interface cable.

droidSSTV - Another SSTV option, but better options exist. 

AndFlmsg - Many supported modes but experience may vary based on your smartphone/tablet.

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