This is a carryover from the thread on the 580.
As I stated in that thread, BCI on 40m can be a huge problem here in Europe.
I'm not talking about the signals themselves being inside the band and
strong, I'm talking about the sum of the voltage from all of them hopelessly
overloading the front-end of the transceiver, causing the noise level (as
seen on the S-Meter) to go up several S-Units across the entire ham band.
How bad is it?
Well on two different Elecraft K2's, connected to a 3-element 40m beam 100
ft. high and pointing north east (towards JA), it pegs the s-meter, full
scale.
And the K2 is supposed to be an excellent rig. Actually it is; the problem
is just bad.
Attenuation and even more attenuation will reduce the problem significantly,
but it also drops the signal level of your QSO partner.
According to Rob Sherwood, as you add in attenuation, the intermodulation
drops 3x as fast as the attenuation.
10dB of attenuation drops the intermodulation by 30dB.
For good radios on average antennas (dipoles at 50'), 20dB of attenuation
was usually enough.
On better antennas, you needed even more, but then the radio could not copy
the weak ones.
The only thing that really helps most radios is an external preselector, but
most radios have no provision for attaching a pre-selector directly in the
internal RX antenna path.
The preselector's attenuation outside of the ham band is 30dB or more,
depending on the quality of the preselector, and that completely eliminates
the intermodulation problem for most good radios.
My Jupiter performed about like the K2: full scale S-meter reading from
noise on 40m (without the preselector).
About 8 years ago, I sent Ten-Tec and Elecraft information about this.
Examples (audio and video files) were posted on the internet for viewing and
listening to.
Results:
- Ten-Tec provisioned for a preselector in the Omni VII at the time
of its announcement. The pre-production unit they sent me to test in Europe
had this option pre-wired to the back panel so I was able to test it with
and without preselector.
- Ten-Tec provisioned for a preselector in the Eagle about 1 month
after its announcement. It's an add-on option.
- Elecraft answered and said I had my radio adjusted wrong. "I" was
the problem. My second email went unanswered.
Since Elecraft refused to create a mod for the K2, I did it myself and it
can be downloaded from my web site, here: http://www.dj0ip.de/downloads/
This is just one of about 300 reasons why I like Ten-Tec, and also why I
like Ten-Tec even better than Elecraft.
Good New / Bad News
The good news is, even though my Eagle is provisioned for the preselector, I
don't need it.
Perhaps it is because the short wave broadcast stations vacated our ham
band.
I didn't need it with the Orion either, even when on the beam, back in the
days when the broadcast stations were still inside the ham band.
The Orion needed just 10dB of attenuation and it was fine. And that was
only when the beam was pointing east. Pointing in any other direction there
was no problem.
The bad news is, I don't have a 3-el. 40m Yagi at 100' at this QTH to see if
the problem exists when using it with the Eagle.
I'll have to lug the Eagle down to Munich some time where I can try it on
that antenna and see.
73
Rick, DJ0IP
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|