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What's at 100 kHz ±

Discussion in 'Radio and Communications' started by jpanhalt, Dec 5, 2015.

  1. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    I am building a LW receiver/amplifier like this: http://sidstation.loudet.org/hw-en.xhtml

    My Max 275 filter (https://www.maximintegrated.com/en/products/analog/analog-filters/MAX275.html ) will arrive (I hope) Monday. I have added some small capacitors (8.2 to 22 pF) across the TL082 op-amps I am using as low-pass filtering. With just three stages ( about 60 dB gain) I am picking up something strong around 100 kHz. My target (center) frequency for this project is 250 kHz. Attached is a really crude LT Spice schematic that shows a close approximation of what I built. Some of the resistor values were changed to accommodate what I had on hand. The capacitor values are what I used.

    What could it be? Location = NE Ohio about 40 miles West of Cleveland. My first assumption is it is some sort of oscillation that I will need to deal with. But just in case someone knows of a LW beacon in the area, I thought I would ask.

    John

    Edit: In real life, the coupling capacitors are not shorted. I did that to see the effects on the simulation.
     

    Attached Files:

    Last edited: Dec 5, 2015
  2. JimB

    JimB Super Moderator Most Helpful Member

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    There is a navigation system called LORAN which is on 100kHz. Sounds like a rough noise when you listen to it.

    JimB
     
  3. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    Good morning Jim,

    I remember LORAN C from my pre-GPS days. The Seneca Great Lakes station ( outside Rochester, NY) transmitted at 1 MW and is about 300 miles away. However, all USA stations apparently stopped transmitting in 2010.

    On further investigation (I fixed my antenna and used the shorter of the two coils), I believe the frequency is closer to 53 kHz and comes from my Tek TDS210 scope. It is quite strong and directional (saturates my "receiver"). Here it is this morning:
    52 kHz_Capture.PNG



    Here it is after partially shielding it with the hat I wear ;) :
    upload_2015-12-6_7-14-36.png

    Can't wait for my tuning IC to come tomorrow.

    On a slightly related subject, ICOM makes a couple of models that are called affordable when new. The portable ICOM IC-R6 (blocked for cell phone) is about $200 and the desk model IC-R75 is about $650. Do you or other hams here have any opinions about either model?

    Regards, John
     
  4. dave

    Dave New Member

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  5. JimB

    JimB Super Moderator Most Helpful Member

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    I have an IC-R72 which is the predecessor of the R75 I believe.
    The R72 is a competent receiver. I use it as a general purpose bench receiver for listening to ... whatever needs listening to on my workbench.

    It was very secondhand when it was given to me, it had spent a hard life on a North Sea fishing boat. Even now when the case is removed, there is the smell of stale cigarettes inside.
    One day if I get the inspiration, I will replace all the push buttons on the front panel. The cigarette fumes make them a bit intermittent in operation.

    JimB
     
  6. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    UPDATE: The 'scope has a 47 uF/450V capacitor for the screen backlight power supply. It read about 1.5 Ω, but was very slightly puffed. I replaced it with a new cap (ESR = 0.53 Ω), wiggled the copper Brillo pad connecting the case to ground, and it works fine now. Noise on the signal channels is a little now than before, and I don't detect the interference at 53kHz.

    John
     
  7. zahwi

    zahwi Member

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    Gary350 is developing his 100KHz induction heater, how far he lives from you?
     
  8. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    Not walking distance. Google Maps is a good resource to get a more accurate distance from Cleveland, Ohio to Murfressburg, TN. It's about 512 miles.

    John
     
  9. Mikebits

    Mikebits Well-Known Member

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    So John, what is your interest in Solar activity? Is this to help you determine HF signal propagation on a given day based on solar activity?
    I recall when I was stationed on a ship, we had this rack of gear called a CHIRP sounder, what it did was determine the best usable HF frequencies to use on a given day.
     
  10. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    No interest in solar activity here.

    John
     
  11. Mikebits

    Mikebits Well-Known Member

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