Pages: [1]   Go Down

Author Topic: Icom 746/756 on MARS Frequencies  (Read 19164 times)

N3SKO

  • Member
  • Posts: 69
    • homeURL
Icom 746/756 on MARS Frequencies
« on: November 20, 2003, 02:03:26 PM »

One of the Delaware Army MARS members received this email from Icom Technical Support after having some issues with power output on a MARS 5 MHz (AKA 60 Meters) frequency.

QUOTE:
Good Morning....

Thanks for your e-mail.

The 746 final PA band pass filters were never designed to support operation outside of the amateur radio bands.  They will "stretch" to accept normal operation in the MARS and CAP frequencies just above and just below the amateur radio spectrum, but they will not support operation down in the 5 MHz area.  They will heat up and you will damage the radio.  About the only two radios will have reasonable operation on the 5 MHz area are the 706MkIIG and the 718.  

END QUOTE

MARS members might want to research their choice of radios closely as a large number of our spectrum is not adjacent to the amateur bands.

73,
john
AAT3BF/AAM3O/AAA3DE/AAA9AC
Logged

KC5FM

  • Member
  • Posts: 39
    • homeURL
Icom 746/756 on MARS Frequencies
« Reply #1 on: November 21, 2003, 12:15:52 PM »

http://www.mods.dk/ is a collection of MODS for all radios.

I hope you find it useful.

The disclaimer is something along the line "If you do the MOD you void the warranty.  Mods do not necessarily work all the time."  That protects the author.     :)

Let me know how more I can help.


Lloyd Colston      Mayes County CEM
Pryor, OK USA      http://www.geocities.com/mccem
   When Danger comes, it is too late to plan.
Logged

NC3Z

  • Member
  • Posts: 10
    • HomeURL
Icom 746/756 on MARS Frequencies
« Reply #2 on: November 23, 2003, 12:17:59 PM »

The Icom 756Pro reflector had some info on this a while ago. As many users have noticed the power out on 5Mhz was only about 50W even though the input power was the same as for a 100W out.

As the Icom message indicates it was being wasted by the output filters. About 4.7 Mhz seems to be the upper limit and then it picks up again in the low 6Mhz.

Since the regional SHARES freq is in that area too I just use my Harris, Sunair or Raytheon radios that are designed to cover all freqs. Some of these rigs can be purchased for very reasonable costs, or via the MARS equipment program.

For example the Raytheon Ray-152 was being sold in quantity from a local surplus dealer for about $200. It was in very good cosmetic condition but needed new PA transistors and a new keypad. The transistors were $35 for the pair and a new keypad (from JRC as they are who really makes the radio) was less than $20. After that I had a nice 150W all mode, 1.6-30Mhz rig with a standard .3PPM TCXO.

I figured it's cheaper than abusing my 756Pro and 746Pro.
Logged

KC5FM

  • Member
  • Posts: 39
    • homeURL
Icom 746/756 on MARS Frequencies
« Reply #3 on: December 07, 2003, 11:20:09 AM »

Here's a reply I received from ICOM:

"Thank you for contacting ICOM Technical Support.
 
Currently we do not have any approved mods for the 60 meter band. We
will post them on our website just as soon as our engineers have
completed their evaluations.

Steve Burling
Technical Support Representative
 
ICOM America, Inc.
2380 116th Ave NE
Bellevue, WA 98004
Ph.  (425) 454-7619
Fax (425) 637-8417
www.icomamerica.com"

Lloyd Colston                    Mayes County CEM
Pryor, OK USA      http://www.geocities.com/mccem  
      When Danger comes, it is too late to plan.
Logged

K8JDC

  • Member
  • Posts: 0
Icom 746/756 on MARS Frequencies
« Reply #4 on: December 13, 2003, 01:47:46 PM »

I'm curious about this topic.  I have been using my 746 (non-Pro) to participate in a MARS net between the 80m and 40m bands.  I certainly don't want to damage the radio.  I would be interested in hearing from 746/756 owners who use their radios in this range (including the 60m amateur band).  Has anybody experienced problems with this?

JDC
Logged

KC5FM

  • Member
  • Posts: 39
    • homeURL
Icom 746/756 on MARS Frequencies
« Reply #5 on: December 13, 2003, 03:54:06 PM »

I have an ICOM 745 that I use on MARS and 60 meters.  I don't run it at full power.  It seems to work fine.

I don't know about the 746, but there's a power output control on the front panel.  I keep mine at minium, unless I am close to the ham bands.  Even then, I find that I am heard, regardless.  

Let me know how more I can help.

Lloyd Colston      Mayes County CEM
Pryor, OK USA      http://www.geocities.com/mccem
   When Danger comes, it is too late to plan.
Logged

N1TS

  • Member
  • Posts: 5
Icom 746/756 on MARS Frequencies
« Reply #6 on: December 22, 2003, 06:14:55 PM »

You can use it safely on the MARS frequencies close the amateur bands with the exception of the 60 meter band. I use a 756 Pro on MARS every day, just not on the freqs near 60.

I did exchange email with a ham who had come up with a mod to switch the correct band pass filter in for 60 meters, but he hasn't shared details.

Logged

KB9ZB

  • Member
  • Posts: 113
Icom 746/756 on MARS Frequencies
« Reply #7 on: December 25, 2003, 11:49:44 AM »

The icom also has another issue, the aux jack on thr rear does not support usb digital modes. It seams that the yaesu and icom brands aonly support the ham convention, and will not use usb below the 20 meter split. You can go through the front pannel and use the mike jack, it's the only way to get this beast to think USB.
I use my keenwod for the digital stuff as it does not care .
ron
Logged

W0RY

  • Member
  • Posts: 18
    • homeURL
Icom 746/756 on MARS Frequencies
« Reply #8 on: March 14, 2004, 11:25:50 PM »

What model of ICOM are you referring to that doesn't support USB on the rear panel?

My 756PRO works exceptionally well for Digital modes in USB or LSB.
Logged
Pages: [1]   Go Up