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Voltage Drop On Transmit - Resolved


marcspaz

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If you are new to radio, hopefully this will be helpful information for getting the most out of your radio.

 

Normally, when I install a radio in one of my vehicles, I cut off all the connectors and run my own lines from the battery to the radio.  Occasionally, my GMRS radio gets moves between 2 vehicles, so I left the factory T connector on it.  Turns out, that was a big mistake for performance.

 

I had a few people tell me that my signal would be very good for a second and then rapidly drop to a weak signal.  I ran a field strength test and the voltage would peak at 77.5 V/m on initial key, and almost instantly drop to 65.7 V/m.  That is a huge drop.

 

Knowing what to look for, I measured the power from the battery on the cold side of the T connector and it was 14.0v while on stand-by.  However, when I key up, the voltage dropped to 12.4v. A couple of times, it dropped to 12.1v.  On the hot side of the connector, there was only 0.25v drop on key-up.

 

I cut the T connector off and soldered in some Power Pole connectors, which have more surface area and much higher spring tension.  Now, I only have 0.25v drop on the input of the radio and my field strength is holding steady at 77.5 V/m while transmitting.

 

To give you an idea of how much drop that is in usable power, it is the equivalent of changing your antenna feed from about 37 watts to 50 watts (assuming an antenna with no gain and 100% antenna efficiency). So, if you want to get the most out of your radio, ditch your glass fuses (weak squeeze connector) for a blade fuse and replace your factory T connector with either a fully soldered connection or a high quality Power Pole style connector.

 

Note:  I could resolve the 0.25v drop if I run a larger diameter power and ground cables... but it's not worth the effort for my application.

 

Hope this helps.

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Some good info.

 

I was going to run a 4 gauge wire to 12 gauge inside of my truck to power a Ftm 400. Running through a relay to a blade fuse to have key on power. But switched to a straight 12 gauge wire run and just going to run the apo. Using the inline glass fuse.

 

Guess I will be hunting for a 12 gauge inline ato fuse setup noq.

 

Sent from my SAMSUNG-SM-G891A using Tapatalk

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I ran a 4 gauge line from the battery, through a 100 am circuit breaker.  Then connected it to a 100 amp circuit block, with each fuse bus being rated for 30 amps.  From the fuse bus block, I ran 14 gauge.  All bolt down except for the fuse itself. 

 

I think I should have run 12 gauge, and then I wouldn't see any drop.  Its all run through the interior and don't feel like pulling it all apart.  Too much work.  LOL

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I don't blame you for that. If it's cool enough tomorrow, I hope to install my shiny-new FT-857D and ATAS 120 in my little Toyota Camry, so while at it I'll straighten up the other three radio's wiring! :lol:

 

I'm so jealous.  I was just looking at the FT-857D... but good grief, that is expensive for a mobile.  Please let me know how you like it.  Especially if you do the MARS/CAP mod.  I may pick one up in a couple of months.

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I'm so jealous.  I was just looking at the FT-857D... but good grief, that is expensive for a mobile.  Please let me know how you like it.  Especially if you do the MARS/CAP mod.  I may pick one up in a couple of months.

Marc, I got really lucky. I spotted an eBay listing for the FT-857D complete with a Portable Zero 857 sprint/escort (side rail frames, battery box and carrying shoulder strap) for truly portable operations...

 

...at a real bargain price of $650. The original owner had bought it and never even took it out of the box! He sold it to the second owner who only tried it twice before changing his mind and buying a KX-3 and Panadapter instead.

 

So I've wound up as the third owner of a nearly virgin transceiver! Even with the ~$50 shipping costs, it was still cheaper that buying all of the stuff "new in unopened boxes." Oh yes, I also got the optional DTMF microphone in addition to the stock mic. wink.png

 

Excuse the crappy photo, but my camera phone isn't the best on the planet for pictures, nor is it worth a darn as a phone for that matter! Anyway, the only thing I've bought is the ATAS 120A* (auto-tuning mobile antenna) and the battery/charger as shown in the forefront of the radio. I just got it charged up but haven't installed it in the box on top of the radio yet. I'll likely do that after I eat this evening.

 

I'll start a new thread once I've gotten it installed in my car and share some pictures.

 

* ATAS 120A: https://www.gigaparts.com/yaesu-atas-120a.html?gclid=EAIaIQobChMI4szC0_jn4wIVBJ6fCh1RLgB0EAQYASABEgLMevD_BwE $389 at Gigaparts.

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Marc how did you figure you had a powerloss? Swr?

 

Also, an ATAS 120 on a Camry... that should be a sight to see rolling down the road.

 

Now I am thinking I should pull the 12 gauge out put the 4 gauge to the secondary battery power and ground. Run that to the dual 4 gauge distribution blocks. To run everything. What are the chances of getting RFI that way? Especially, if i run multiple batteries and usb hubs off of that as power and ground?

 

Sent from my SAMSUNG-SM-G891A using Tapatalk

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Also, an ATAS 120 on a Camry... that should be a sight to see rolling down the road.

Fortunately, I a Diamond fold-over mount I'm going to repurpose for the ATAS 120A. I just need to open the trunk and it will fold over neatly into the trunk and be totally hidden.

 

I installed it temporarily yesterday and took a quick drive down the Indiana Toll Road as it has a 70 mph speed limit. No problems were noted

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Curious what your long term opinion is. Everything I have read has not much nice to say about. Could just be everyone comparing it to its predecessor which a lot seemed to like.

Are you asking about the ATAS 120 (prior model) or something else?

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Marc....

 

Wow!  That looks great and is one heck of a deal!  Congrats!  Looking forward to seeing the new thread.

 

 

Marc how did you figure you had a powerloss? Swr?

 

It was based on signal reports from other stations.  As soon as I got the reports, since the radio was nice and cool, I automatically assumed line voltage drop would be the most likely problem.  The next thing I would have looked for was SWR (bad antenna ground, etc.).  Going back a bit more than 20 years ago, I worked in radiotelegraph.

 

 

Now I am thinking I should pull the 12 gauge out put the 4 gauge to the secondary battery power and ground. Run that to the dual 4 gauge distribution blocks. To run everything. What are the chances of getting RFI that way? Especially, if i run multiple batteries and usb hubs off of that as power and ground?

 

RFI is most frequently caused by either proximity to the antenna being too close, bad RF shielding on the transmission line or improper output grounding.  That is not exclusive, but frequent.

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