Guys, I apologize for possible scaring a few people here.
I want to point out a few important facts about pre-selectors.
First of all, the problem on the 40m band, and to some extent on 80 and 20,
was always a European (only) problem.
The shortwave broadcast stations simply were not loud enough in the states
to cause a significant RX overload problem.
To us here in Europe they were very real, BUT . . .
Things have changed here as well.
In the past, our 40m ham band was from 7.0 to 7.1 MHz. (that's it).
We also had shortwave broadcast stations operating within our band.
In the meantime our ham band has been expanded 100 kHz, going up to 7.2 MHz.
AND more important, all of the short wave broadcast stations have moved
outside of our band.
As I said in a previous post, the front end can be overloaded by the sum of
the RF voltage arriving from the antenna, into the front end. All of the
shortwave broadcast stations operating within the band were asserting a very
high power level on the front end of all receivers. ALL of that has gone
away now!
AGAIN, this was NEVER a problem in the USA. It was only a problem here in
EU.
However, the examples I showed you clearly show the difference in the two
types of technologies: 'Upward conversion' vs. 'Downward conversion'. The
Downward conversion is about 20 dB better. YOU CAN TAKE THAT NUMBER TO THE
BANK.
So how does all of this affect you (and me) today?
For most of us, not at all. Forget it.
You will only see a difference if you are participating in a Multi-Multi
contesting event and have several stations at the same QTH running 1500w, or
perhaps in a Field Day operation where you have lots of transmitters on the
air at the same time, especially on 40m and 20m where we often see two
stations on the air on the same band at the same time; one on CW, the other
on SSB. In cases like these, the 20dB will be apparent. For all other
cases, you won't notice a difference.
For most of us operating from home, we will never encounter a situation
where a preselector would help.
The exception would be if you have 2 or 3 contesters living within a mile of
each other, all on the air at the same time. Then you might encounter a
situation where a pre-selector would help.
Also, as previously stated, you may be encountering disturbance from strong
local broadcast stations. Yes a preselector would help here, but the
cheapest and easiest solution is to buy a High Pass Filter (100w version)
that you can even transmit through. Simply insert this in the antenna line
and it will take care of your problem.
I apologize if I scared people into believing they must buy a pre-selector.
It would be a very rare event if you must.
Any questions, please contact me off reflector at Rick@DJ0IP.DE
73
Rick, DJ0IP
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