VHF lowband to 10m FM

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by KA2FIR, Oct 8, 2018.

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  1. KA2FIR

    KA2FIR Ham Member QRZ Page


    Which commercial vhf low mobiles will easily and cheaply convert to 10M fm? How would a Syntor rate? Desire good sensitivity and selectivity.


  2. KB4QAA

    KB4QAA XML Subscriber QRZ Page

    -If you need more sensitivity, slap a preamp in front. Build or buy an inexpensive one.
    Last edited: Oct 8, 2018
  3. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    Even on 10-meters, the ambient noise level exceeds the rated sensitivity of all low band FM units. Also, the limiter circuits in FM receivers are designed to eliminate all AM components and noise is AM.

    There are a relatively few 25.0 MHz to 28.0 MHz commercial FM units that, generally, make it to 29.5 MHz easily. Any 29.7 MHz to 36 MHz (or 30.0 MHz to 36 MHz) unit will tune down without any problems. Those units for the 36.0 MHz to 42.0 MHz take way too much effort to make it to either 29.5 MHz or to 52.5 MHz. The 42.0 MHz to 50.0 MHz units usually make it to 52.5 MHz without too much work (if any) but forget about going down to the 10-meter band.

    Glen, K9STH
  4. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    I built a 29.6 MHz repeater from a Motorola Micor (~100W) mobile rig many years ago. It wasn't difficult, but had to bring out a separate RX input connection, etc.

    I never put that on the air, just tested it a lot and then sold it. It was put on the air by a station in PA; that was back in about 1977 so who knows if it still exists. It might...the darn Micors were close to bulletproof.:p
  5. WA4ILH

    WA4ILH Subscriber QRZ Page

    This may be a bit off topic but, with today’s “narrow band” technology, (modulation index of 1 or less) why don’t we start using NB on some new 10 meter FM repeaters? We could then legally transmit FM below 29.5 allowing a larger split between repeater input and output. Now, 100 KHz split seems a bit narrow for a low band repeater. There would be less desense if the split was 500 Khz. or so. (as an example) Of course, that would ruffle some feathers from some other users such as the AM boys or whoever uses the frequency range between 28.8 to 29.0 MHz.
    Tom WA4ILH
    KE8FWJ likes this.
  6. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page


    47 CFR Part 97 Section 97.205(b) reads as follows:

    (b) A repeater may receive and retransmit only on the 10 m and shorter wavelength frequency bands except the 28.0-29.5 MHz, 50.0-51.0 MHz, 144.0-144.5 MHz, 145.5-146.0 MHz, 222.00-222.15 MHz, 431.0-433.0 Mhz, and 435.0-438.0 Mhz segments.

    Therefore, an input, or output, below 29.5 MHz is not allowed!

    Glen, K9STH
    K5VZD likes this.
  7. WA4ILH

    WA4ILH Subscriber QRZ Page

    Point taken Glen but, rules can be changed. We now have low band equipment that can operate reliably at a lower bandwidth then the old standard +/- 5 KHz deviation.
    Tom WA4ILH
  8. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    Actually, there has been NBFM equipment available since World War II with a modulation index less than 1 which is perfectly legal below 29.0 MHz. FM / PM with a modulation index over 1 is allowed anywhere phone operation is legal above 29.0 MHz and +/- 5 kHz deviation has a modulation index of 1.66667. The frequency 29.300 MHz is a very common simplex FM frequency in Asia and it is definitely possible to work Japanese stations on that frequency.

    One could try to get repeaters legal below 29.5 MHz. However, that would probably be an uphill battle with a lot of objections from those who do not like having repeaters on HF.

    Glen, K9STH
  9. W0GSQ

    W0GSQ Ham Member QRZ Page

    I use a 50 watt Maxtrac. Did nothing to the receiver, only mod was the manual power control from the Repeater Builder website.
    I've used it off and on for the last 13 years.
  10. W0GSQ

    W0GSQ Ham Member QRZ Page

    I've worked many JA's over the years on 29.300.
    Sunspots help.

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