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  1. #1
    Member
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    External Antenna Question

    I was wondering why you would need to add an external antenna (ie. LGC-4000) to an HDS sonar?
    They already have an antenna built into the unit. Can someone explain why and the advantages?

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  3. Member
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    #2
    The external has a refresh rate of 5x per second while the built in antennas are 1x per second. I have mine hooked to two units with the antenna mounted as close to the trolling motor transducer as I can get it.

  4. Member
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    #3
    Same here. Five times faster refresh rate. Mount as close to transducer either trolling motor or transom mounted for best readings for waypoints etc. I have mine connected vis a vis NMEA 2000 to both my HDS-8's

    Michael J.
    I wish that I could be half the man my dogs think I am.

    Mapleleaf-Mick/
    A Loyal Lowrance Supporter since 1964
    18.5 foot Fiberglass Lund with a 200hp outboard and 80 lb. thrust bow mount trolling motor
    Outrigged for walleye fishing with two HDS - 8's (one first gen and one 2nd gen), LSS-1, LSS-2,
    Sonic Hub, full NMEA 2000 Network with LGC 4000, Point-1 GPS and Livewell Temp Sensor.

  5. Member
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    #4
    They can also be used in locations where the top of the sonar unit is obstructed in the case of a center console boat with a t-top.

    I find that updating the rate 5x per second and mounting them near your transducer is a waste of money. The GPS info is not that accurate unless you receive a WAAS signal.

  6. Member
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    #5
    Makes sense but now another question.
    Why mount it as close to the transducer as possible? Wouldn't you just mount it in a spot where it has good reception of the satellite signals?

  7. Member
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    #6
    I mount my external antenna directly overtop of my StructureScan and my regular transducer. The purpose is for accuracy when saving waypoints by using the cursor (crosshairs) placed on either my StructureScan screen image or my regular sonar image. By zooming in and using the crosshairs directly on the structure or on fish, you get the best possible accuracy when your antenna is close to your transducers.

    I wrote a 3 part article about this in the current (and next two) issue(s) of Bass Angler's Magazine.
    ciao,
    Marc

  8. Member
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    #7
    Got it now!!
    Thanks for the explanation. Makes sense now....!!

  9. Member
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    #8
    Marc is dead on the money. You are already 5-8 off if you are marking waypoints from what you see on sonar at the console if you are using the unit internal gps and the transducer is on the transom. External antennas should be mounted as close as possible over a transducer.



    1992 18FDX ASTRO 150 MERC

  10. Member
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    #9
    Thought the 4000 gave you the WAAS signal

  11. Member
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    #10
    Quote Originally Posted by TomzRanger View Post
    Thought the 4000 gave you the WAAS signal
    Nope, It can acquire the signal but so can the 3000 and the internal antenna. All depends on your location and how the government is feeling that day.

  12. Member
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    #11
    There are three possible realms for improvement by use of an external antenna instead of an internal antenna in a Lowrance HDS chart plotter and SONAR:

    --by locating an external GPS receiver sensor and the SONAR sensor in the same place, there will be better correlation between the position deduced by the GPS receiver and the echoes received by the SONAR; without the co-location there is a random error in the position of the GPS receiver internal sensor relative to the SONAR sensor; the distance between them is fixed but the orientation of the boat is random;

    --by using an external GPS receiver the sensor can be located with a clearer view of the sky; this can be especially advantageous in receiving signals from the geo-stationary satellites of the FAA's WAAS space segment, which are often at low elevation angles for users in eastern North America;

    --by using an external GPS receiver there may be possible improvements in sensitivity, number of satellites tracked, and speed of position solutions, if the external GPS receiver is actually better than the internal GPS receiver in the HDS units.

    The Lowrance LGC-4000 is not a particularly outstanding GPS receiver in my view because it is not particularly more sensitive than the internal receivers, and it does not track any more satellites than the internal receivers. The LGC-4000 cannot track the GLONASS satellites. The LGC-4000 can offer a marginal improvement in speed of position solutions. The HDS typically does position solutions updates at a rate of 2-per-second; the LGC-4000 is said to be able to do 5-per-second.

    --
    Last edited by jimh; 11-28-2012 at 09:39 AM.

  13. Member
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    #12
    If you are bank beater type fisherman then there is no advantage using a external antenna. But if you are a deepwater/offshore structure type fisherman then yes there is a advantage. The key is making sure your external antenna is close as possible to or sitting over the transducer for pinpoint accuracy of locating structure.



    1992 18FDX ASTRO 150 MERC