The following is a brief comparison of the latest K2 (s/n 4606) and the
ORION (s/n 10C10593) on the 40m band, tonight (28-FEB-05).
Here in Europe we are troubled by interference from very strong shortwave
broadcast stations. Most transceivers cannot operate on 40m at night on a
decent antenna without their receivers deteriorating significantly from
strong intermodulation. I'll call these "Ghost signals" for now. These
ghost signals are signals which are not really present (theoretically) but
are indeed alive and kicking (and QRMing). These signals consist of both a
carrier and modulation. The carrier can easily be so strong that it
desensitizes the RX (with AGC) significantly. The most common cures for
this are:
1) turn off the preamplifier;
2) use significant attenuation;
3) use an external preselector.
Those of you living in the states and having never personally experienced
our European conditions probably do not appreciate the degree of trouble
this causes us. Most serious contesters I know own at least one
preselector. I own three.
On the Internet you can find several tables of measurements of IP3, BDR,
etc, but these are just numbers. When one radio is 3 dB better or worse
than another, what does that actually translate to in performance? How
good is "good enough"?
The rubber meets the road when you actually hook an antenna to the radio and
try to use it under adverse conditions.
For these tests, I use my two antennas:
1. Openwire-fed horizontal dipole, total length 40m (~125 ft.), up 13m
(~42 ft.)
2. Openwire-fed vertical dipole, total length 12m (~38 ft.), feedpoint
9m (~28 ft.) high.
Both antennas are matched with high-power Annecke symmetrical matchboxes.
They have identical circuitry, though one is rated 600w and the other is
rated 1500w. I repeated the test with the matchboxes swapped, just to be on
the safe side. Swapping the matchboxes made no difference.
RESULTS:
On the horizontal antenna:
* The Orion's receiver is "clean" across the entire 40m band, even
with the preamplifier on
* The K2 is "clean" across the band with the preamplifier off, but
with it on there are quite a few ghost signals to be heard, though they are
only about S1 or S2.
On the vertical antenna:
* The Orion is "clean" across the entire 40m band with the
preamplifier off, but with it on there are a few very weak (S1 or less)
ghosts to be heard
* The K2 with preamplifier on has a band full of ghosts, 59+20 dB or
more. You simply cannot operate the radio this way. With the preamplifier
off, there are still a number of ghosts that are S4 to S5. With 10dB of
attenuation, there are no more ghosts to be heard, but weak signals also
fall into the noise. Using a high-quality external preselector (with 6 dB
insertion loss), the K2 with preamplifier on is "clean" across the entire
band. This is how I will use it.
At this time of night, the vertical is usually a better antenna (stations
are a bit stronger) than the horizontal antenna. Without the external
preselector, it really didn't help to use the vertical antenna on the K2.
On the Orion, most stations are stronger on the vertical.
Conclusions:
* There is a significant difference in RX deterioration due to IMD on
40m at night when on the vertical antenna. The Orion simply doesn't care,
whereas the K2's performance suffers significantly
* There is a slight difference in RX deterioration due to IMD on 40m
at night when on the horizontal antenna. The Orion is the clear winner with
preamplifiers on, but with preamplifiers off, it's a wash
Comments:
* My K2 is brand new. It was built by a retired RF engineer
(previously with Siemens). It appears to be functioning properly but it
hasn't been measured thoroughly. I will give it to another engineer who has
the test environment to check the K2 thoroughly. Until I have confirmed the
condition of my K2, I caution readers not to place too much confidence in
the results of this short test.
* This is my third K2 (so I am familiar with the radio) and until
trying this specific test tonight on 40m with the vertical antenna, I was
confident it was working perfectly well. Maybe it is, but maybe there is
something causing my particular unit to be more susceptible to IMD than it
should be.
* My Orion is my home QTH station and my K2 is my portable station.
Both are used for CW contesting. I am confident that the K2 used with the
external preselector (which is not much larger than a pack of cigarettes)
will meet or exceed my portable contesting requirements.
Am I disappointed? Not really. For the cost and size of the K2, it's one
heck of a radio and probably the most bangs for the bucks on the market -
but it's not an Orion.
As I always say, "It's horses for courses".
73
Rick
DJ0IP / NJ0IP
Munich, Germany
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