LF Receiver

Discussion in 'The Low Bands - 630/2200 Meters - VLF' started by AC0OB, Nov 10, 2019.

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  1. AC0OB

    AC0OB Platinum Subscriber Platinum Subscriber QRZ Page

    I have been contemplating a simple homebrew receiver for some time that covers about 130kHz to 480 kHz.

    I wanted to source most parts from my stock on hand using discrete components; no PICs, just SS analog circuitry. I will add one of those Chinese frequency counters later.

    I think the varactor tuning at the mixer will provide more tuning resolution than would an open air mechanical variable.

    I am leaning toward the page 2 mixer which simply winds the antenna coil around L2.

    I have bread boarded only the LF Detector thus far so component values on the mixer and IF Amp may change.

    Some of the circuit ideas were adapted/adopted from a friend's 5W 75m transceiver design.

    So I am just throwing this out there and wondering if anyone else has homebuilt an LF receiver.


    Pheel
     

    Attached Files:

    Last edited: Nov 10, 2019
  2. KL7AJ

    KL7AJ XML Subscriber QRZ Page

    Howdy:
    I have a homebrew direct conversion receiver, using a function generator as the local oscillator. Very clean and stable. I'm using a minicircuits DBM, but you can easily build one with a couple of toroidal transformers and some germanium diodes. The AF amp is three cascaded FET voltage amplifiers...very simple...and sensitive. My next phase is to build a front end preselector, but so far I haven't had any overload problems.
    DC receivers have the definite advantage of no internally generated birdies....kind of an important thing at LF.
     
  3. K1LKP

    K1LKP Platinum Subscriber Platinum Subscriber QRZ Page

  4. N0UU

    N0UU Ham Member QRZ Page

    You are in for an adventure. Start simple from you junk box. It will work. Filters are easy down there. Low noise devices are handy, but you might not need. Switching mixers are handy as most IM happens on the rise and fall of the LO so digital signal to the mixer is a must.While the DSP front ends are now the rage, you can get really good results with analog. Build modular and have fun. N0UU
     
    AC0OB likes this.
  5. KL7AJ

    KL7AJ XML Subscriber QRZ Page

    That Ham Up looks interesting, but it converts up to VHF which wouldn't do me any good. If the thing converted to HF somewhere, I'd jump right on it.
     
  6. KM1H

    KM1H Ham Member QRZ Page

    Pheel, Ill suggest just the opposite!

    Pick up an old USN RAK, 1934 RCA design TRF (who pretty much owned the maritime radio market) and used into the 60's on some ships which is where I experienced it at first.....and be prepared for one of the best LF/MF radios made for CW. It might require getting someone to help lift it! Selectivity is excellent as is the audio limiter on static. Very sensitive AND quiet.

    Mine is a RAK-7 which had all the upgrades and I also have the matching RAL-7. The original PS and cable may be hard to find but building one is simple at a fraction of its weight.

    Carl
     
  7. N0UU

    N0UU Ham Member QRZ Page

    Those Navy beasts all have probably narrow front in filtering and probably two stages...to prevent any possible radiation of the LO. Didn't want the enemy to DF on the leakage. Not sure how careful they were with dynamic range as often they would be in isolation except in a convoy when even then they would be quiet. Anyway, the mechanical work was as good or better than you can readily buy today. Good choice. N0UU
     
  8. K1LKP

    K1LKP Platinum Subscriber Platinum Subscriber QRZ Page

    CARL,

    ENJOY,,,,



    THATS WHAT THE RADIO ROOM LOOKED LIKE WHEN I FIRST WENT ON THE
    USS TIGRONE SS-419 .....(1961 - 1965)

    THEN UNCLE SAM SENT US INTO THE PHILLY SHIP YARDS FOR AN OVERHAUL
    AND WE RECEIVED THE LATEST AND GREATEST TOYS ......

    COLLINS URC-32 AND THE R-390A AND THE SRR SERRIES OF VLF RX

    73 AND KEEP SAFE WITH THIS DARNED CORONA VIRUS GONG AROUND
     
  9. KM1H

    KM1H Ham Member QRZ Page

    That SX-25 doesnt pass muster as mil spec!!

    I was on USS Wacamaw AO-109 1961-63 and the RAK RAL were back in Emergency Radio where the ET shak was also located. Radio Central had the RBA, RBB, and RBC for CW and AM and a recently installed URC-32 for slopbucket.....I ran lots of phone patches with that.

    This in an old photo, I couldnt find a good one from the early 60's before she was jumboized. When fully loaded with fuel and/or water ballast and in a storm she just plowed thru with a ~33' draft....not a small ship!

    [​IMG]
     

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