On 10/30/09 15:31 , Gregg wrote:
On Oct 30, 9:30 am, "D. Peter
wrote:
On 10/30/09 04:37 , wrote:





On Oct 29, 11:18 pm, "D. Peter
wrote:
On 10/29/09 22:00 , wrote:

On Oct 29, 10:52 pm, "D. Peter
wrote:
On 10/29/09 21:50 , wrote:

Hi folks,

A little while ago, I was goofing around with the Long Wave band on my
radio. I picked up Radio Havana, and some other stations that are
usually found on Short Wave.

Why? Can anybody explain this?

Thanks!!
Barry F.

Which radio are you using for this?

Hi,

I'm using a new Roberts Revival R250 with slide rule dial.

Ok, that helps. A number of possibilities, here. Cross modulation
product. And image. And overload product. Radio Habana is a strong
signal, and on receivers with less headroom and substandard image
rejection or filtration, overload is common on particularly strong
signals. This can create images up and down the dial, even on different
bands.

You may have signal mixing somewhere in your local environment, with
the lower product falling into the LW band.

If the issue exists on all your LW receivers, it's less likely to be
an issue that originates within the receiver.

Hi, this morning I tried a different radio, and picked up an AM
station on the lower end of the LW band. This time there no Short Wave
stations on either radio's LW band both picked up the same AM station.

By the way, this Roberts Revival Radio has the most sensitive AM and
FM bands, it compares to my CC Radio.

Sounds like you've got a strong local signal in your area that's
producing mix products in your receivers. Likely that AM. But it can
also be a strong local FM, or even a stray signal from an unexpected
source. Like another electronic device.

Consumer grade receivers, like your Roberts, are designed and
constructed to provide effective performance on anemic antennae. To
make this work, the front end has to be quite sensitive. To meet a
price point, manufacturers will cut corners. So, some assumptions
are made about where and under what circumstances the radio will be
used. Top of the list, is that high level signals are not expected
to be encountered. So, high sensitivity input circuits are designed,
with little room for the occasional high signal level that may never
be encountered. These input circuits are usually run wide open,
without provision for reducing input to prevent overload. Further
savings are achieved by eliminating internal shielding between
stages. What you end up with, is a receiver of high sensitivity
that, under certain conditions, produces spurious signals up and
down the dial.

If the spurious signals on your LW band are different on each
radio, the problem is one or more local signals with enough signal
strength to produce non linearities in the first RF stage, which
produces mix products of multiple signals that appear on more than
just your LW band. They'll likely be on SW, as well.

Eliminating these spurious signals may be as simple as reducing
the amount of antenna available to your receiver.

But strong local signals can also get in to your receiver though
other paths than the antenna. If you're powering your radio with an
A/C adaptor, disconnect it, and run your radio on battery power. If
that eliminates the spurious signals, you've isolated the path by
which the problem signal gets into your radio. Ferrite cores on the
DC line to your radio from the wall wart will reduce this signal. As
will using a filtered, regulated power supply with an effective ground.

A little investigation will reveal what the offending signal is,
and where it may be coming into your radios. With that, you can take
measures to reduce spurious signals and enjoy your radio as it was
intended to be enjoyed.- Hide quoted text -

- Show quoted text -

Great post Peter as usual.



Thanks. Although, I'm sure this will start another barfight. Grab
a beer and enjoy the show.