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Icom 718 modifications

Discussion in 'The Low Bands - 630/2200 Meters - VLF' started by N0DZQ, Oct 5, 2018.

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  1. N0DZQ

    N0DZQ Ham Member QRZ Page

    I was wondering if anyone has been successful in modifying an Icom 718 to transmit on 630 meters?

    Thanks in advance for any information!
     
  2. K8JD

    K8JD Ham Member QRZ Page

    A transverter makes more sense than building filters for 630M and try jamming them inside the 718 !
     
  3. WB5WPA

    WB5WPA Ham Member QRZ Page

    One filter, outside the rig, A lowpass filter, killing the second and third, etc. harmonic is really all that should be necessary.

    I threw one together for my Icom, to knock harmonic energy down ... PLUS, my antenna (a tuned vertical loop) is resonant at 475 kHz, further attenuating any harmonic content.
     
  4. WB5WPA

    WB5WPA Ham Member QRZ Page

    Some of the earlier 706MK2 would. Don't know about the 718. The G 706 didn't seem very happy at all and wouldn't do above a couple watts at 475 kHz.
     
  5. KM1H

    KM1H Ham Member QRZ Page

    Run 630M directly out the transverter port at the ~10 milliwatt level and add an amp with filtering for whatever power you need. No need to fry the rigs finals trying to force power thru them.

    Carl
     
    W1TRY likes this.
  6. WQ2H

    WQ2H QRZ Lifetime Member #214 Platinum Subscriber Life Member QRZ Page

    Dennison's book has relatively simple LPFs for both 630 & 2200.

    But I think the antenna may be the long pole in the tent. Good luck ! :)

    73
    Jim, WQ2H
     
  7. WB5WPA

    WB5WPA Ham Member QRZ Page

    Have you even looked at the schematics for those rigs? The series of AC-coupling caps in the preceding stages present such a high capacitive reactance at 475 kHz that there isn't enough RF energy coming down the pike to the 'finals' to so-called 'fry' them ... PLUS the inter-stage 'magnetics' are also a limiting factor ... face it, everything is "working against you" when you take a radio down about two octaves (by a factor of almost 4 frequency-wise) from where it was designed to work.
     
  8. WB5WPA

    WB5WPA Ham Member QRZ Page

    re: "But I think the antenna may be the long pole in the tent. Good luck ! :)"

    16 ft x 40 ft (Vert x Horz) tuned loop fits in a city-lot back yard. Check QRZ bio page for WSPR performance with 5W RF at 630 meters into that somewhat inefficient loop of wire (I don't claim it is efficient, not when I' m only using 10 ga. copper wire). But, that can be an advantage, lower Q means wider BW, and the inefficiency can be made up for by running 'a few more watts' to arrive at the effective radiated power (ERP) limits.
     
  9. KM1H

    KM1H Ham Member QRZ Page


    No I havent and thanks for that info.

    I see that as another good reason to use the transverter I/O port for those rigs that can be enabled on 630 and have that port available. It would also make a rig with cooked drivers/finals a much cheaper purchase.....I did that years ago with a TS-940 and pulled that whole section plus the ATU and added transverters in their place. It worked well in that respect but the rigs horrible phase noise caused me to purchase 3 TS-830's (back when they were real cheap) for 6M to microwave transverters.

    Is there any FT8 activity on the band? If so I would use that rather than wait forever for those very slow modes...if feasible.

    Carl
     

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