[MRCA] MX-7777

Tue Jan 14 14:08:17 EST 2020

If you get a MX-7777 I think the thing is to remove the two power output connectors on each side and the rear power input connector and use three heavy cables to provide the DC input to the breaker, DC output from the top of the MOV and a equally heavy ground cable or strap from the frame ground to the battery ground. I have the DC input run directly to the battery with an inline 60A fuse that I salvaged from an old 2200 watt UPS, a ground from the MX frame to the negative terminal of the battery along with the strap that came with the MX to the frame and the last cable that comes out to an isolated stud in the battery compartment that provides the protected DC output to the radios.
The MX has a 50 or 60A breaker that's in line with its input and if overvoltage is beyond its ability to control it will throw the breaker and remove the distribution from the potential overvoltage. The battel override bypasses the circuit breaker and MOV so if it was in theory an excessive over voltage you still have the ability to damage the radios by defeating the MOV function and using battel override.
There are also some weird components that are on top and sensing the current thru the MOV that look like they have a capability to trip the big breaker somehow. Not certain of their function.
The MX-7777 is a newer component then was ever installed on the older vehicles but I don't think I would do an install without one because of the additional protection it provides.  My experience only applies to the more modern VRC/GRC stuff with solid state power supplies and don't know what would happen if you used an older radio that has a dynamotor and with high current inrush and would think the circuit breaker they use may not like it.
Attached is the DC distribution that is on the mutt. All cables to and from the MX are #6, the big cables to the GRC-106 are the stock DC (coaxial) power cables and the VRC-12 power cable is the stock power cable and they all terminate in the battery box as per the recommended installation instructions. For reasons that are beyond my own understanding there are also the huge 0 gauge cables that run to the slave connector that connect directly to the battery and a 0 gauge cable that runs to the starter switch on the floor of the mutt that has a # 8 or 6 that goes to the alternator on the engine. The starter switch on the floor of the mutt appears to be the DC distribution point for the mutt so you can take advantage of the pulse generated by the starter.
An interesting footnote, somehow there are always dead UPS systems laying around work. For a long time it was cheaper to replace some of our 2200 watt rack mount UPS system then spend the money on replacing the batteries. Old high power UPS systems provide a lot of useful parts including high current interconnects, heavy gauge red and black wire an on the older large units things like fairly high current transformers. The APC UPS has a big transformer with a three tap 120 volt secondary and a 12 volt primary that's great for 12.5 power supplies or a car battery charger.

Ray F/KA3EKH

From: mrca-bounces at mailman.qth.net <mrca-bounces at mailman.qth.net> On Behalf Of KA1LHZ
Sent: Tuesday, January 14, 2020 9:15 AM
To: mrca at mailman.qth.net
Subject: Re: [MRCA] [MMRCG] Todays M&S Net

I had an issue with my GRC-106 where I apparently fried the input filter capacitor. I followed the troubleshooting  in the -35 TM and it was the first fix in the troubleshooting chart. It was a real treat to replace it (AAAGH!!) as it's located behind the front panel of the RT-834. Now I'm always careful to make sure everything is shut off when starting the M-37. I've looked at the MX-7777 surge suppressors but not sure where I'd mount it in the truck or the MSC-37 shelter. It was a valuable lesson, albeit frustrating that I broke my radio.

73

DE KA1LHZ
On 1/12/20 5:24 PM, W2HX wrote:
Very interesting about the MX-7777. I never really knew much about it other than general purpose surge suppressing. Found a funny cartoon talking about it. (google books, this link should take you there)

https://books.google.com/books?id=GMs8AAAAYAAJ&pg=PA52&lpg=PA52&dq=MX-7777+surge+suppressor&source=bl&ots=Y_EJi2wVXl&sig=ACfU3U2aSfYFI9LVIJTv-gIkMJuOXiKZlw&hl=en&ppis=_e&sa=X&ved=2ahUKEwisy4jOjP_mAhXSg-AKHbJxAtcQ6AEwAnoECAoQAQ#v=onepage&q=MX-7777%20surge%20suppressor&f=false

From: MMRCG at groups.io<mailto:MMRCG at groups.io> <MMRCG at groups.io><mailto:MMRCG at groups.io> On Behalf Of Ray Fantini
Sent: Sunday, January 12, 2020 12:42 PM
To: Mkdorney <mkdorney at aol.com><mailto:mkdorney at aol.com>; J Mcvey <ac2eu at yahoo.com><mailto:ac2eu at yahoo.com>
Cc: mrca at mailman.qth.net<mailto:mrca at mailman.qth.net>; MMRCG at groups.io<mailto:MMRCG at groups.io>; MICHAEL ST ANGELO <mstangelo at comcast.net><mailto:mstangelo at comcast.net>
Subject: Re: [MMRCG] [MRCA] Todays M&S Net

Just for fun I tried to do every part of the GRC-106 installation exactly as prescribed. Including locating the correct antenna mounts, feed thru and power cables including the conduit that runs across the mutt's deck. But one place that I deviated was to install a MX-7777 surge suppressor assembly in the tool compartment located next to the battery compartment. That's connected to two studs in the battery compartment, one that connected to a 60A fuse and the two batteries and the second stud feeds the two cables to the GRC-106, the VRC-12 system on the passenger side of the mutt and an accessory feed that runs things like the URC-110 that comes along for VHF work.
The two batteries are also connected to a slave connector on the front of the mutt and most times I can connect a MEP-025 1.5 kW 28 volt generator via a fifty foot cable or like yesterday can also use the slave connector to connect a AC power supply that feeds the mutts electrical system. The mutt has an onboard 60A alternator but try to avoid running the engine whenever possible due to the fact that the engine leaks oil a lot.
The MX-7777 is a great box. First it gives you a concealed place in the tool compartment where you can disconnect all the DC to the radios via the front power switch the second and best thing is that they have some form of huge diode / MOV in it that can limit power below 30 volt regardless of what happens to the input. I played around with one on the bench and saw it conduct massive amounts of current to ground but not damage itself.
And if it did ever fail it has a "Battle Override" switch that can bypass its function.

Ray F/KA3EKH

________________________________
From: Mkdorney <mkdorney at aol.com<mailto:mkdorney at aol.com>>
Sent: Saturday, January 11, 2020 10:40 PM
To: J Mcvey
Cc: mrca at mailman.qth.net<mailto:mrca at mailman.qth.net>; MMRCG at groups.io<mailto:MMRCG at groups.io>; MICHAEL ST ANGELO; Ray Fantini
Subject: Re: [MRCA] Todays M&S Net

We had a GRC-106 on my M151A2 in Greece if the Jeep wasn't running, we were supposed to shut down completely before starting the Jeep,then we could turn it back on. There was no restriction as far as transmitting if the 1/4 ton was running or we shut it down. We only had to shut down the GRC106 when the 1/4 ton was off and we were going to start it.

Mark D.
WW2RDO

"In matters of style, float with the current. In matters of Principle, stand like a rock. ".   -   Thomas Jefferson

On Jan 11, 2020, at 6:04 PM, J Mcvey via MRCA <mrca at mailman.qth.net<mailto:mrca at mailman.qth.net>> wrote:

Can you start  the jeep after transmitting or do you leave it running?
On Saturday, January 11, 2020, 3:38:43 PM EST, Ray Fantini <rafantini at salisbury.edu<mailto:rafantini at salisbury.edu>> wrote:

thought I had a recent picture of the mutt in the yard but just checked the phone and no joy! did not take one this afternoon but do have plenty pictures of the mutt in field operations on my web page at:

http://staff.salisbury.edu/~rafantini/

recent pictures from Gilbert MRCA and York MVPA about half the way down the page.

Ray F/KA3EKH

________________________________
From: MICHAEL ST ANGELO <mstangelo at comcast.net<mailto:mstangelo at comcast.net>>
Sent: Saturday, January 11, 2020 2:28 PM
To: Ray Fantini; mrca at mailman.qth.net<mailto:mrca at mailman.qth.net>; MMRCG at groups.io<mailto:MMRCG at groups.io>
Subject: Re: [MRCA] Todays M&S Net

Ray,

Glad to hear you. I am normally the southernmost station in Leonardo NJ but  your Salisbury signal was coming in loud.

Would you have a picture of your setup? The wife was in the shack at the time and would like to see it.

73 Mike N2MS
On January 11, 2020 at 2:16 PM Ray Fantini <RAFANTINI at salisbury.edu<mailto:RAFANTINI at salisbury.edu>> wrote:

was great to drag out the mutt (M-151) and fire up the GRC-106 and make the net this afternoon. Its seventy degrees and sunny, nothing like you would expect for January!Was on the MMRCG net at ten this morning after getting out of bed ten of ten. Had I known the weather would have been like this would have attempted to get up early  and run the radio in the mutt for that net too.

Field radios are happy in the field! Not on the shelf or basement.

Ray F/KA3EKH

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