[TowerTalk] Transceiver Specifications
Sun, 02 Jul 2000 17:45:35 -0700
Dean: The receiver characteristics you noted are all measures of a
radios ability to withstand very large signals near one you are
listening to. When overloaded by very large signals, radios generate
spurious signals which may interfere with a weak one you are listening
to. This performance is what you pay big bucks for in the top line
Even the inexpensive radios produced in the last 10 years or so have
very low MDS (minimum descernable signal). This is sometimes called
noise floor or front end noise. In the interest of simplicity, I won't
throw numbers at you but the atmospheric noise coming in on your antenna
on the 160-10m bands is practically always much greater than your radios
internal noise. You can test this very easily. Tune to a part of the
band with no stations and note the noise level. Disconnect your antenna
coax and see if the noise level doesn't drop considerably. If your radio
passes this test, you need a better antenna to receive weaker signals.
If your radio noise does not change when the antenna coax is removed,
either the antenna has serious problems or the r.f. stage in your radio
73, Dan, N5AR
Dean Wooldridge wrote:
> I created a spreadsheet with the various numbers from the ARRL transceiver
> reviews hoping to find patterns. I didn't find any obvious patterns and I
> confess I don't even know why the various numbers are important! That tells
> me I need to back up and cover some ground that I missed.
> In the ARRL advanced and extra class study guides there is some information
> that talks about things like receiver blocking, two-tone 3rd order IMD, etc.
> but I guess I'm looking for a bit more real world advice. Question is:
> Are the measurements you find in ARRL reviews such as receiver blocking,
> two-tone, 3rd order IMD, 3rd order input intercept, and the like really
> valuable in the decision to purchase a radio?
> Can you really tell the difference between one measurement of say 106dB and
> 108dB (whatever the measurement is)?
> My ICOM-725 has some numbers that are as good or better than a 756PRO or
> FT-920 yet there are signals I cannot hear when a fellow ham 2 miles from my
> QTH can hear them on her FT-1000. We use virtually identical antennas (my
> R5, her R-7000). I'm trying to improve my hearing and minimize noise (QRM).
> I suspect I need to invest energy in the antenna system. What I'm trying to
> do is figure out if the specification differences in the radios amount to
> anything compared to changes in antenna configuration.
> Big questions, appreciate any feedback.
> dean (K5DMP)
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