K2, broadcasting on 40mt

[Silvio IZ5DIY]

I'm just running first test on my "almost finished" K2/100.
I'm sorry but I have my S/N at the moment, but it's 6XXX series. One of
the latest.
I miss just SSB (missing parts coming), but I have KAF2, NB, 160mt, and
100W.

Some weeks ago I had few test experience at first step of construction:
K2 (cw - qrp) having lot of fun on ARRL CW test.
I get California on 40mt 10W, and that was the first qso on 40mt for my
new K2. Not too bad!
Other qso to USA on 20mt and 15mt, and a LU on 10mt. So tests were on
different band with good results.
I can compare signal by switching to IC775, just to be sure K2 wasn't
deaf. And it wasn't!

After many evening of pleased work I add NB, 160mt, KAF2 and 100W. So
last weekend (was so rainy!) I complete all (except SSB as I said).
Last evening I where on air listening and making some test.
I found strong broadcasting interference on 40mt, I check again,
changing antenna from PA to RX, same strong interference.
Many interferences were on 7.0 - 7.1 band (Italy has just 100 KHz).
Next I noticed I had "PRE" on. Switched off and problem disappears.

My previous test on 40mt (ARRL CW) was on daylight time (late
afternoon), not at night time like last one. So I cannot say if problem
was added by new features (NB/KAF2/160mt/100W) or it was there even at
first step.

I try to handle few test: removed KPA100, going back to K2 configuration
(plus NB/KAF2/160mt). Same interference with preamp on, disappear
switching off.

So I wonder if this "problem" is a common problem and if I can set it as
a problem ... you are right: I am putting more pre-amp to a noisy band,
close to strong broadcast signal here in EU at night time... so maybe
it's just enough.
Or if something I did was not right in my handwork. Any more test to
run? any parts to check?

73, Silvio IZ5DIY  (also K6DIY)
www.arimpt.org/iz5diy

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[Roelof Bakker]

Hello Silvio,

At night the BCB signal levels are very high here in Europe.
This excludes the use of the pre-amplifier on 7 MHz.
However using a dipole or similar arrangement the pre-amp is not necessary
at all.

There have been reported some solutions by aligning the band pass filter for
a narrower frequency range, but at my location this is not really needed.

To answer your question, yes this problem is normal behaviour for the K2.

73,
Roelof Bakker, pa0rdt
K2 # 6177


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[g3ymc]

Silvio IZ5DIY wrote

Last evening I where on air listening and making some test.
I found strong broadcasting interference on 40mt, I check again,
changing antenna from PA to RX, same strong interference.
Many interferences were on 7.0 - 7.1 band (Italy has just 100 KHz).
Next I noticed I had "PRE" on. Switched off and problem disappears.

I have occasionally noticed small intermodulation products from broadcast stations on 40 with my K2. They are normally pretty weak and disappear with the preamp switched off. In Europe it needs a pretty good receiver to work close to the MWatt stations and the K2 performance although excellent is not quite there. But have consolation, my first rig, a Yaesu FT201, was virtually unusable on 40m at night, attenuator or not. Things have come along a lot over the years.

73 Dave G3YMC