Homebrew BA receiver design...

Discussion in '"Boat Anchor" & Classic Equipment' started by N2EY, Apr 16, 2018 at 3:51 AM.

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  1. N2EY

    N2EY Ham Member QRZ Page

    That's really good. I suspect that the low frequency of the VFO makes a big difference.

    Yes it does - at the price of size and metalwork. But if you wanted miniaturization, you'd be using ICs and SMT.

    ...bwaaahaaahaaa......

    And they all have to be aligned.

    Sometimes.

    The Southgate Type 7 uses a drum dial as well. The scale was first made by hand on paper, then removed and drawn on CAD. A few printing tries got the size right, then it was printed on transluscent Mylar, and the scale put on the drum.

    Nothing quite like using a radio you built yourself, is there?

    73 de jim, N2EY
     
    W7UUU likes this.
  2. WB0RIO

    WB0RIO Ham Member QRZ Page

    That's a fantastic resource, Jim. There's more information there than anyone could consume in a lifetime.
    Here's a random pick from the 1944 Annual of Advertising Art:
    RadioRepair.png
     
    N2EY likes this.
  3. N2EY

    N2EY Ham Member QRZ Page

    Who even knew there was an Annual of Advertising Art?

    In case anyone isn't familiar, here's another resource:

    http://www.tubebooks.org/

    It doesn't look like much, but....click on the various links, and there's a ton of great stuff. Tube data from various manufacturers, books like Terman, the 1934 and 1941 ARRL Handbooks and much much more.
     
  4. KK6IYM

    KK6IYM Ham Member QRZ Page

    I was back working on the homebrew boat anchor this past week. I re-wired the variable IF so that the trimmers had the adjustable disc connected to ground--a mistake I had wanted to correct for some time. This greatly improved stability and allows easy and precise adjustment with a metal screwdriver. I also went through the RF section and shortened all the coil leads and secured the coils to the chassis.

    When I fired up the radio last night, the 20 meter band worked fine. The 40 meter band did not. It had birdies all up and down the tuning sequence. I would have concluded it wasn't working at all, except Radio Havana was loud and clear, discussing the election of the new president--a person not named Castro. This was a surprise--because Radio Havana is at about 6.165 MHz--not 7 to 7.5 MHz--the tuning range for my crystal. Oops. The crystal is an HC18/U. I will need to unsolder it to test what is happening with the frequency.

    This morning I substituted a 12.5 MHz crystal for the 11.6 MHz used to tune the 20 meter band. WWV came in loud and clear. I first assumed it was at 15 MHz, but when I checked with my HQ 140 XA, 15 MHz was dead. Besides the WWV signal, there were a number of SW BC stations. Yep, I was down at 9.6 to 10.1 MHz--the received frequency subtracted from the crystal to create the IF. Why my RF coils combined with the RF tuning capacitor placed me there instead of the 15 MHz region is a puzzle. On the plus side, my homebrew outperformed the HQ 140XA for noise to signal and sensitivity. This is pretty good considering my Hammarlund had been my go to receiver for AM shortwave.

    I really think I now need to re-do the RF section so that coils and crystals can be plugged in. That way, it will be easier to experiment with different combinations.

    Norm
     
  5. K9STH

    K9STH Ham Member Staff Member QRZ Page

    IYM:

    Sounds like you have gone from low side injection to high side injection!

    Glen, K9STH
     
  6. KK6IYM

    KK6IYM Ham Member QRZ Page

    Further investigation reveals that I can receive WWV at both 10 and 15 MHz using the same crystal and just a few degrees of dial rotation apart (xtal 12.521 - 2.521 = 10 and 12.521 + 2.479 = 15). So I am actually using both high and low side injection at the same time. Fortunately, the band below 10 MHz is fairly full of stations and above 15 MHz--not so much--otherwise I would have stations on top of each other. In fact if my crystal was 12.5 MHz, I could have WWV at 10 and 15 at the same place on the dial.

    Ideally this situation is prevented from happening by the RF tuning being selective enough to attenuate signals not in the tuning range. The ganged tuning capacitors are 50 p. At lower frequencies they can be fairly selective with a limited range. At higher frequencies--less selective. Using the same crystal for two different sections of the spectrum is fine, but I think I want another coil switched in to make this happen.

    This is why I plan on setting up the RF section for plug in coils until I can sort out the ideal configuration.

    Norm
     
  7. N3DT

    N3DT Ham Member QRZ Page

    I started building a modular receiver from a not too old ARRL handbook from the circuits on HB receivers. I built the AGC and IF board at 3MHz as I remember because I could use the TV crystals for the filter. There were converters for the various bands and RF/Preamps for the input and filters for each band. Then there was the audio chain. It was all built to specs to maximize the AGC action vs the input levels and output. I did get one band working but the VFO was the real bugaboo. I could never come up with a stable VFO for the bandspread and I finally dropped the project. I still have an old Eddystone dial for it. I still have the boards and most of it is all SS with fairly modern transistors (70-80's) and the signals I did hear with it were really nice compared to any store built receiver at the time. I should break it all out and come up with a decent vfo now. As I remember the AGC action was superb. It was all build in boxes from double sided PC board and SMA connectors between the sections..
     
  8. KK6IYM

    KK6IYM Ham Member QRZ Page

    I figured out what is happening on my 40 meter band. The crystal is a HC18/U. I suspect the frequency marked on the case is an overtone frequency. All up and down the dial are hundreds of birdies. By very carefully adjusting the RF tuning capacitor, I can get several stations two or three, maybe more, at each birdie. It appears I have an inter-dimensional radio where all frequencies are next to each other or on top of each other. What fun! If only I had a way of knowing where I was, it would be great. The dial for this band is going to look pretty wild--actually, I have ordered a HC6/U which will be a fundamental--then I will just have high side and low side instead of multi-side injection.

    Norm
     

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