Broadcast Break though on 160m

[Brendan Minish-2]

I have just constructed a K9AY loop system to use a receiving antenna on
160m and since I am now using the RX antenna socket I am noticing a
problem that I haven't seen before with my K2

When I have the RX antenna selected (even with no antenna connected) i
have break though from broadcast stations on 160m. these are not as far as
I can tell local AM stations but are from HF. I can't discover any obvious
(to me anyway) harmonic relationship except that they are inverted (tuning
up in frequency appears to actually tune down the BC band stations

this occurs even with no RX antenna when the RX antenna socket is selected
and the stations are there weakly even with no antennas whatsoever
connected to the K2 (presumably the DC, speaker and key wiring is enough
to pick up quite a signal on hf in Europe)

I can find no  obvious cause except that selecting the RX antenna allows
some stuff to slip past the low pass filters ?

I only see this on 160m as far as I can tell.

73
Brendan EI6IZ


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Brendan Minish

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Brendan EI6IZ <[hidden email]>

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[n6wg]

Hello Brendan
I don't have BC breakthrough here, but I do have a number of BC transmitters
nearby, here on the edge of San Francisco Bay.
I build my own preamplifiers with bandpass filters for 160m.  I use them
with
my full size Flag receiving loop.  They would also be appropriate for the
K9AY loop.
You might put together a simple two stage bandpass filter and try that in
the receive feedline to see if it gets rid of the BC signals.

One other thought.  If you have a signal generator, you might try slowly
sweeping it across 160m to see if it beats with those signals.  It might
help determine what frequencies they are really on.
Good luck and 73
Bob N6WG

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[Jim Brown-10]

On Sat, 9 Oct 2004 08:32:54 -0700, Bob Tellefsen wrote:

>I don't have BC breakthrough here, but I do have a number of BC transmitters
>nearby, here on the edge of San Francisco Bay.

I hear intermod from broadcast stations here in Chicago, but I'm pretty sure that it is
externally generated and re-radiated. Why do I think that?  First, I have an ICE BCB filter
between the antenna switcher and my radios. Second, the intermod cuts in and out. Third,
it shows up in several radios, all of them with very good front ends.


Jim Brown  K9YC


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[Brendan Minish-2]

Hi Bob
Good suggestions but the problem is that the unwanted signals don't appear
to be actually coming in to the K2 via the RX antenna socket at all. It's
simply that they are audible when it is selected. I hear them even with no
RX antenna connected (& i can even hear them very weakly when the RX ant
is selected and I have no antenna connected whatsoever. the power, Key and
speaker leads  (presumably in conjunction with all my other shack wiring )
are enough of an antenna to just be able to detect the break though.

They are not MW ('AM') broadcast stations but are I think from one of the
HF broadcast bands. The nearest MW transmitter to me is well over 100
miles away. Yet Evening time Skywave HF Broadcast band signals can reach
as high as -8 dBm on the 7.1 MHz, 9.5 & 12 MHz broadcast bands on my log
Yagi.


Bob Tellefsen said:
> Hello Brendan
> I don't have BC breakthrough here, but I do have a number of BC
> transmitters
> nearby, here on the edge of San Francisco Bay.
> I build my own preamplifiers with bandpass filters for 160m.  I use them
with
> my full size Flag receiving loop.  They would also be appropriate for
the K9AY loop.
> You might put together a simple two stage bandpass filter and try that
in the receive feedline to see if it gets rid of the BC signals.
>
> One other thought.  If you have a signal generator, you might try slowly
sweeping it across 160m to see if it beats with those signals.  It might
help determine what frequencies they are really on.
> Good luck and 73
> Bob N6WG
>
>


--
Brendan EI6IZ



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Brendan Minish

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[Kurt Cramer]

This sounds like an image. The IF is 4.915 MHz and I think the VCO will
be 1.9 above the IF, or 6.815 MHz to receive 1.9. The image would be
11.73 MHz. Am I right? If I am then, I don't know why the bandpass
filters are not putting them way down. But if the signal injection is
not coming from the antenna.....?

I'm not an SWL so is that 11.7 range a broadcast band?

73, Kurt                        

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[Brendan Minish-2]

On Sat, 2004-10-09 at 13:09 -0700, Kurt Cramer wrote:
> This sounds like an image. The IF is 4.915 MHz and I think the VCO will
> be 1.9 above the IF, or 6.815 MHz to receive 1.9. The image would be
> 11.73 MHz. Am I right? If I am then, I don't know why the bandpass
> filters are not putting them way down. But if the signal injection is
> not coming from the antenna.....?


Yes the image reception is of the 11.7 Mhz broadcast band (25m band) and
it's only those 'monster' signals that manage to get in. In the Early
evening I see signals as big as -10dBm here on the 25 M band so it
probably takes the combined efforts of the bandpass filters and the TX
low pass filters to tame signals that large..

if it was just getting in via the RX antenna socket I would put a Low
pass filter in line with my RX antenna but merely activating the RX
antenna seems to allow the ingress to occur even when no rx antenna is
connected. The RX antenna circuit bypasses the output low pass filters
when activated so I guess that's the route in.

Modding the K2 to connect the RX antenna after the LP filters looks like
it isn't a practical option but I wonder if a trap for the 25mb
broadcast band can be engineered (hacked!) into the K2 before the band
pass filters to give some more rejection?

73
Brendan EI6IZ


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Brendan EI6IZ <[hidden email]>

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