“The Virgin” – A DC 40M Receiver

My first HF receiver project is complete.

It’s not fancy. It’s rock-bound with no ability to QSY. It only has a single RF gain control up front. It’s direct conversion, so it hears all signals on both sides of its frequency. It’s bodged together and probably not super durable.But it’s my own, made from scratch, and I couldn’t be more happy. So without further ado, here’s the finished product:

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The Virgin Receiver – safe for use, if not safe for work.
I received this (scandalous!) container in a White Elephant gift exchange at a holiday party this Christmas, and I immediately thought it would make a good home for a radio. It seems a fitting case for the receiver that’s taking my homebrewing virginity.

schemeit-project(1)
The Virgin DC Receiver. Two IC’s and a power regulator. One knob. No fuss.
The circuit is nothing particularly new: it’s based, as I’ve said before, on the work of Dave Richards AA7EE, some fine projects from GQRP, and a very useful document from Bill KV2AWC. The unit is a direct-conversion receiver based around the ubiquitous NE602/NE612  mixer/oscillator IC and an LM386 audio amplifier circuit. Gain is controlled solely by the RF gain pot in the front-end. I find this provides more than enough gain control. There’s also a position for a jumper to boost the audio output from the LM386, but with the amount of RF noise in my apartment, this proves more detrimental than helpful. I may turn that jumper into a switch if experimentation shows its use.

The only filtering present is the handful of passives that sit between the NE602 and the LM386, filtering the audio a bit between converting to baseband and the audio amplification stage. A little experimentation showed that the present passives only seem to round off higher audio frequencies, say about 6 khz. They’re not really meant to enhance selectivity, but just to reduce noise introduced by signals further away from zero beat.

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A naked view of the inside of the receiver. Avert your eyes, children!
I found some nice panel-mount BNC connectors at our local Fry’s electronics, and fitted some Anderson Powerpole pigtails as a power input. (Pro-tip: if you use Powerpoles regularly, as I do in my theatre job, get yourself a ratcheting crimper. Less than $40, will change your life.) There’s a 1/8″ jack attached to one side and the RF gain control is mounted up front. The whole thing weighs maybe half a pound.

Signals come in clear and hot on this thing! With minimal audio filtering and just a basic front end filter, it’s pretty wide open, but that’s kind of the point – at this point, I’ll take sensitivity over selectivity. Particularly up in the QRS part of the spectrum, I’d rather be able to hear the one guy who’s within 3kHz of my crystal than lose him. Remember, this thing is rockbound, so changing frequencies means swapping in new crystals.

The receiver has gone through several revisions and adjustments in the past couple months. See the original post, changes to the front end, and some power problems for those adventures.

While I’ll probably never really be ‘done’ with this receiver – with tinkering projects, are we ever really done? – it feels great to have it packaged up, in a case, and usable. It’s freeing to have something complete enough to show off.

Hear you on the air!

73

 

 

Fried Green Arduinos

It was only a matter of time until something blew up. And last night, it was TWO things.

The first one was my own darn fault  – I’ve been playing around with some simple transistor amplifier circuits, and mis-read one of the transistor data sheets. When I hooked it up a 12V power source… BANG!

IMG_0064You can see the TO-220 package there, literally split in half by the power of electricity. Zam zam! Turned out I had grounded the emiter and applied 12V to the base of the transistor. It blew apart in my face in a shower of sparks.

So, I desoldered that transistor and replaced it with a little J110 FET I had a pile of from my last trip to California. While messing around with the supply voltage, I kept switching a clip lead back and forth between 5V coming out of the 5V rail on an arduino an 12V directly from and SLA battery. Unfortunately, at one point, I disconnected the clip from the circuit and ended up connecting the Arduino directly to 12V…

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You can’t make radios without breaking a few toys. Thankfully, the Si5351 breakout and the nice LCD screen I had hooked up were unscathed. Another sacrifice to the radio gods.

73

Update 2/29: I’ve toasted another one! I’ve been using my old Duemilanove to work on a transmitter project, and apparently relying on its little 5V regulator to power an LCD screen, an Si5351 breakout, and provide bias current to the finals was just too much for the little thing….

First Received Code! (W1AW)

Today, for the very first time, I copied CW that was on the air! Though my morse is still very poor and slow, here’s what I pulled out:

CH?S_  … W1A?… ..HQ STATIONS INQR____SES EXCITEMENT… AND ADDING TO THE INTRIGUE IS THE … _OR. END OF 5 WPM TEXT. QST 1_ DEC…. AG….

What luck! I’d caught the end of a W1AW code bulletin! Pretty neat for the first code I’ve picked out on the air. Here’s how it happened:

I was noodling noodling around putting my Direct Conversion Receiver into a new enclosure (more on that later). The receiver is rock-bound to whatever crystal is sitting in a bit of female header next to the NE602 Mixer. I tend to leave the 7.030 Mhz crystal in there when I’m experimenting – it seems like big-signal stations seem to congregate down in the Extra portion of the CW band, and that extra oomph is helpful when I’m testing a new receiver with an improvised antenna.

After doing a preliminary fitting of the receiver in its enclosure, and a quick repair (yes, it helps to restore all the connections), was I ever surprised when I applied power and my earbuds leapt to life with clear, slow code! Most QRS (slow code) stations seem to be up in the 7.050 to 7.055 portion of the band. What the heck was this very slow, loud station doing so low in the band?

I grabbed a nearby post-it note and started copying, and pulled out the code above. I know I butchered a bunch of it, even at 5WPM, but it was very exciting to (a) hear un-anticipated CW come over the airwaves and (b) to be able to actually copy some of it!

For my own reference (and others’), here are the W1AW Slow-Code transmission times, both in UTC and CST:

Day CST UTC
Monday 4pm 000z
Tuesday 2pm, 8pm 2100z, 300z
Wednesday 4pm 000z
Thursday 2pm, 8pm 2100z, 300z
Friday 4pm 000z

Hear you on the air! But only if you transmit very, very slowly.

73