Using a GPS Repeater Antenna with the Yaesu FTM400DR

My Yaesu FTM-400DR has had a difficult time ascertaining a GPS lock inside of my vehicle. Some others have also complained of this, but when my radio is in my...

My Yaesu FTM-400DR has had a difficult time ascertaining a GPS lock inside of my vehicle. Some others have also complained of this, but when my radio is in my 2nd story shack @ home, or if its out in the open during field day, it picks up a signal relatively fast (<30 seconds usually). I’ve decided to keep the FTM400DR in the truck due to the interactive screen (as opposed to the plain ole TM-V71A’s face). I just found that having a touch screen in a vehicle can be really convenient, especially for quick adjustments when your stopped.


On a trip out a few weeks ago, the FTM400DR took almost 30 minutes before it was able to get a lock. I figured it was the laptop blocking the signal, so I completely rotated it out of the way, but still no dice. Found another YouTube video by KC8MTV showcasing this GPS repeater antenna he found that just might be a good option.

I paid about $25 for quick shipping w/ Amazon, but you can find them cheaper on eBay (or possibly other retailers). If so, and you’d like to share, please comment below! I think this is a relatively easy and cheap enough fix.


A GPS lock is not exactly necessary to do C4FM, but it is necessary for the APRS modem to start sending out your beacon. Plus it also puts some additional ‘neat’ factor in – when you know exactly how far away the other guy is! Even when it would get a lock on a signal, it would occasionally lose signal. So this device is a huge boost because of the external antenna having a clear view of the sky. My truck is essentially a big shield, this is why HT’s never work well with their attached antennas inside a vehicle. To add to the mix, my truck was tinted by an aftermarket guy, and I’m pretty certain it’s a metallic tint of some sort (as opposed to ceramic) which blocks signals even further. Putting the FTM-400DR on the dash, just wasn’t an option for me, that would’ve been the only ‘patch’ that I could apply, but with this, the unit has a clear view of the sky. I’m guessing this device could also provide a better GPS signal to your phone, but phones primarily use cell towers anyways to obtain a gps lock.


The external antenna is magnetic, but I plan on mounting something under the unit to prevent the usual problems associated with mag mounts. We’ll see how long the unit lasts in the brutal Texas heat, i’ll have to keep an eye on it over the coming months. I’m tempted to silicone the coax attachment point better, as I see this as the only possible point of water ingress. The coax was thin enough that I was able to slide it in between the rear window and rubber seal, the coax was extremely long though, I had lots of excess so had to loop it up and stow it away. The wires really are starting to pile up in my truck, I’m determined to keep them neat and tidy though!


As I understand it, the FTM-400XDR has an improved GPS antenna (it has an improved 66 channel GPS receiver) and doesn’t suffer from the same ailments, but even a good GPS antenna inside a shielded car will still suffer from occasional spottiness I imagine. I’m sure this is no new device to most, but I had no clue GPS repeater antennas existed, so I had to share!




APRSMobileToyota TacomaVHF/UHF AntennasVHF/UHF OperatingYaesu FTM400DRYouTube Videos
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