On Mar 28, 10:12 am, "Pete KE9OA" wrote:
I have been an RF Engineer, specializing in low level RF design since 1992.
Why are we having this conversation in the first place? The reason for my
post was to clarify which mechanism was responsible for the manifestation
that the original poster was experiencing.
To glibly state that this was an image problem is clearly misinformation.
Too much of that going around these days. Mini-Circuits has a very good
tutorial on this subject on their website.
Now, what does being a professional frequency coordinator have to do with RF
engineering principles, specifically, small signal RF design? I have no
doubt that you have experience in this area, and the 900kHz frequency that
the original poster mentioned can confuse the issue if is is assumed that
the receiver has a 450kHz I.F. which it may or may not have..........many
receivers over the years used a 455kHz I.F. which would place the primary
image 910kHz below the actual frequency. A simple analysis of this problem
clearly shows that it is a 3rd order IMD problem.
For other folks out there that may be interested, 3rd order intermodulation
products don't exclusively occur only in mixers.......they can occur in any
nonlinear system, such as oxidized electrical connectors, saturated ferrite
cores in front ends of receivers, bandpass filter switching diodes, crystal
filters, and AGC diodes. It can also occur in rusty rain gutters, or
anywhere else that galvanic corrosion can occur.
I am sorry if you took offense at my post, but next to doing everything to
preserving life, truth is the most important thing in this world.........
thus, the reason for my reply to the original poster.

Pete

It was something that I needed to address that I have been
experiencing in most of my radio receivers that engineers in China
have
trouble fixing. You see, I have a shortwave radio receiver that has
the long wave bands that cover 144 kHz to 353 kHz without no
problems. When I received the G5, this was something that I thought
would replace the Yacht Boy 400 Pro Edition, but it did not
make no improvement for me the LW DXer. I have owned previously
the Sangean (Radio Shack) DX 380, 392, and 390 and since
you mentioned you've been an RF engineer since 1992, well I have owned
the DX-380 since 1992. I have dealt with this problem
even when I used a longwire antenna. I thought hey its just another
radio station on 150 kHz thats rebroadcasting a signal, but
now since I have owned the YB-400 PE radio the station does not appear
on the YB-400PE. It seems that the YB-400PE
has its own LW tuned circuit seperate from the others like AM and SW.
I see why the radio was set at 144 kHz to 353 kHz
They could of extended the coverage to 519 kHz and keep the same tuned
circuit.

You see, if you lived in Europe and you have received stations on LW
from the AM broadcasters you probably have lots of
overloading along with LW and MW radio stations cause of the 900 kHz
signal being such a pain to get rid of. Here do
the math

Above all, this problem has been an issue not just on LW but on AM (MW
as well trying to receive a station on 550 kHz
when you got another station from the 1450 kHz - 900 kHz = 550 kHz
being a problem. This is one reason I had to
one day take some radios apart and get them aligned the best as I can,
good and some bad. I feel that we need to
get this problem fixed on new radios. And about mini circuits
Grundig does not use those parts anymore. So yes I
may have to buy another receiver since Grundig is cheap garbage and
lost its German quality.

Anyways, I got myself a loop antenna and coupler built to reject the
intermod garbage and the signal from 1050 kHz
is gone from 150 kHz. So everything is fine as long as you use a
preselector or a 500 kHz low pass filter. Still I
do appreciate spending $149.99 on something thats suppose to be crap
on LW and gold on AM and SW. Engineers,
give LW a chance for NDB DXers and Transalantic LW DXers. One day
I am going to be releasing information about
transatlantic DXing and form a forum about this subject. This
spring LW transatlantic DX is possible and I have the
cassette tapes to prove and the minidiscs. Thank you very much.


49N4AE and gccengineering





"dave" wrote in message

...

Pete KE9OA wrote:
This can also occur in multiple conversion receivers, depending on the
ultimate rejection of the roofing filters.
In this case, image rejection has nothing to do with it. What is being
experienced are 3rd order IMD products. Do a Google search on 3rd order
IMD products in mixers, and it will become very clear.............

Pete

"dave" wrote in message
...
gccradioscience wrote:
If you live in a city area or some rural area with a real strong AM
station its likely it will be found on the longwave bands from 150 to
519 kHz (1050 kHz to 1419 kHz) the 900 kHz carrier image. Please
understand that this station is not a real longwave radio station.
Its a image from the broadcast station when the station is strong
enough to bleed on other longwave frequencies. The radios that I
have is the DX-380, DX-390, DX-392 and the yes the new Grundig G5.
It has do something with the dual conversion circuitry . I am
hoping that manufactuers, hobbyists, and technicians will use the 900
kHz formula to see other image stations to show that these AM stations
should not be on the LW bands.

Desired AM Station (kHz) - 900 kHz = Image Station

The images I am getting here locally in Virginia Beach, VA on LW is

150 kHz = 1050 kHz WVXX -AM
210 kHz = 1110 kHz WYRM-AM
330 kHz = 1230 kHz WJOI -AM
410 kHz = 1310 kHz WGH-AM
450 kHz = 1350 kHz WGPL -AM
500 kHz = 1400 kHz WPCE-AM

AM Band Images that are annoying

550 kHz = 1450 kHz
650 kHz = 1550 kHz

Adam E.

It's a single-conversion phenomenom usually. Two times the IF, + or -
the FOI.

Sir, I am a professional frequency coordinator and need no schooling on
3rd order IMD.

My trusty Philips AE-3805 (Sangean innards) has a big gap in coverage
(7300 kHz-9.500 kHz) that can largely be overcome by tuning 900 kHz either
side of the frequency of interest. 900 kHz is twice the IF. This is the
exact mathematical relationship described in the original post. I suspect
we are arguing over word usage, not the science.

A mixer simply produces a desired intermod product.

One of the few positives of a dual-conversion receiver is their ability to
keep the first image out of the downstream bandpass.