When is more than a few watts power needed?

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by N0PKG, Oct 27, 2015.

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  1. W4SEX

    W4SEX Ham Member QRZ Page

    So you are saying that if I'm standing on a hill looking at a repeater tower that is 5 miles away, that a 1 mw transmit signal from a HT ( just an example of a very low wattage figure) is going to be just as strong as a 65 watt mobile signal?
  2. K0RGR

    K0RGR Premium Subscriber QRZ Page

    After the first wave of surplus commercial FM gear, the next phase was commercial gear built for hams and those rigs were mostly 1 watt or 10 watts. I used a Drake TR-22 as a mobile for a long time, but I was in California, where all the repeaters are on mountains, so 1 watt worked well over some pretty amazing distances. Here in the flatlands, things are much different. The highest level repeaters here are only 300 feet above ground, and most are far lower than that. The antenna for our local SKYWARN repeater is at the top of a 300' tower, but we still recommend a 50 watt mobile for SKYWARN use, because in a heavy rain storm, the signals can be attenuated enough by the rain to make it impossible to get in from the far side of the county with anything less than 50 watts. I have had occasions where I needed to use a bigger mobile antenna in really bad conditions, just to talk across our rather small county.

    As in all things ham related, antennas are the key. One of my students checks in from the far side of the next county over with his 5 watt Baofeng, and sounds like a local most of the time - but he is using a jpole on his roof. There is a repeater just beyond him about 20 miles that I can only reach with 100 watts from my house, though.
  3. K0RGR

    K0RGR Premium Subscriber QRZ Page

    A friend of mine was the trustee for the 146.64 repeater in San Jose years ago. His house was in Sunnyvale, and the repeater is on Loma Prieta, around 30 miles away. He used to test the repeater by seeing what the lowest level signal was that would trip the repeater. He did his tests in microwatts.
  4. KC9UDX

    KC9UDX Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Certainly, based on my little bit of playing around the last few years.

    But I routinely use 100mW from my basement into a repeater 7 miles away, with a lot of trees and hills in the way, too.
    ZL1UZM likes this.
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Of course it won't be.

    You still need enough power to overcome path loss, whatever that is. 1mW to a no-gain antenna at 5 miles likely won't work at all.

    100mW likely will.
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    When I had "my" repeater (I lived on a hilltop and a wide-coverage repeater was at my home, tower in the backyard) in northern NJ years ago I would "test" it from my bench in the engineering lab at Boonton Electronics in Parsippany, almost exactly 20 miles away, using a Boonton 102B RF signal generator and a 19" whip plugged into the N connector on the generator, with the instrument in a rack next to my bench in the lab. Surrounded by metal cabinets, not near a window, inside a building made of brick and cement.

    I could trip the repeater with 20mW (+13 dBm), no problem. That's 20 miles with 20mW and an indoor zero-gain antenna.

    However, it was -- other than the building I was in -- essentially line-of-sight and the repeater had a great receiver.

    As soon as you lose the LOS path things go downhill fast.
  7. W4SEX

    W4SEX Ham Member QRZ Page

    read the above statement from KC9UDX "Certainly, based on my little bit of playing around the last few years. "

    both of you cannot be right, so I'm on your side Steven. I'll let you guys hash this out.:p
  8. W7CJD

    W7CJD Ham Member QRZ Page

    These are great examples: there is something else that happens and I haven't quite figured it out: sometimes one repeater, 60 miles distant, comes in like "gang busters".

    . . .

    I want to say, we are required to use the minimum power for the communication.

    I have heard requests for RST however I have never heard anyone reduce power and ask for RST while reaching for the minimum power for communication.
  9. KC9UDX

    KC9UDX Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    But, we aren't. If we were, all those repeaters would be in violation.

    The desired communications could mean always bending the needle of the other station's S-meter.
    K3XR likes this.
  10. KK4YWN

    KK4YWN Ham Member QRZ Page

    Crank it all up to eleven and use the widest bandwidth you can. This is professional amateur radio.

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