Jeff DePolo wrote:
>>If we were talking about 6-meters, I'd agree on the 6-dB
>>disadvantage in
>>the mobile environment. I've never seen anything like that on UHF. I
>>don't buy into this argument yet ;-)
>>
>>Chuck
>>WB2EDV
>>
>>
>
>OK, if you don't like the mobile noise environment model, let's just look at
>raw sensitivity and ignore degradation due to ambient noise issues. Would
>you not agree that a good UHF repeater receiver with a GaAsFET ahead of it
>will have better sensitivity than a typical mobile radio? If so, by what
>amount?
>
>
No. A "typical" UHF ham rig will have better sensitivity than most
repeaters with a preamp. A commercial mobile (without preamp) will have
sensitivity slightly worse than the repeater with the preamp. 99% of
hams will be using a ham rig, not a commercial one.
>There are some mobile radios out there that are quite hot. But my
>experiences have been that the hotter the mobile radio, the more prone to
>intermod and overload it is. The high sensitivity comes at a price - lack
>of front end filtering. Where I live, "intermod alley" seems to be more
>like "intermod county" thanks to Kenwood's wonderful receiver design, which
>is why I use it only as a dial-around radio when I'm travelling but
>otherwise I rely on an oldie-but-goodie commercial radio for working the
>local repeaters.
>
>
Yep. You may experience more intermod with the hotter receiver, but the
intermod is most likely going to swamp the mobile receiver no matter
what power level the repeater is running, at least most of the time.
I'll stand by my original comment. A single site UHF repeater need not
run gobs of power to stay balanced with a typical 35 watt ham mobile.
The repeater's gains and losses to it's TX and RX will be the same. So
to that point everything is pretty much equal. So, if we are to argue
that the mobile receive environment is harsher (and at UHF I don't think
it really is), I can see running a bit more repeater transmit power just
to be safe. If we kick in another 3dB that would take us to 70 watts out
of the transmitter. In my mind that should do it, but going beyond 100
watts would be excessive for a single-site installation.
I'd be interested in someone actually trying this with a UHF system that
is running 200+ watts. Drop it to 100 watts without telling anyone.
Leave it there for a week or two and see if anyone notices. But you
can't tip your hand. Or if you do say something, tell people you made
some improvements at the site and listen for comments.
Chuck
WB2EDV
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