Saturday, January 31, 2009

Crystal locked 80m direct conversion receiver

To go with my recently constructed 80m double side band transmitter, I've just completed a crystal locked direct conversion receiver.

DC receiver.jpg

The circuit is based on the Neophyte receiver from QST except that I used a crystal oscillator configuration in place of the LC controlled one.

It's an NE602 connected to the antenna via a single tuned stage, with balanced audio feeding an LM386 audio amplifier.

As you can see, it's very simple. I spend more money on boxes than on all the components.

I purchased a bunch of common crystals at 3.5795Mhz and have put one in the receiver and another in the DSB transmitter. I zero beat the residual carrier to match their frequency.

As Peter Parker commented on an earlier post, I am able to hear DSB on a DC receiver. He said that frequency stability was more important that with SSB reception so I went for a crystal locked receiver.

The next thing I need is a nice way to switch RF and power between transmitter and receiver - currently this process is rather cumbersome and takes too long.

I'll see if I can find someone for a fully home brew contact with me.

Update: First fully home brew contact

To make it a bit more practical to switch between receive and transmit I've constructed a switch box that switches both RF and DC between two sides.

The whole set up looks like this, the switch box is on the left:


While I did have to ring up VK2BVS to get him to tune to my crystal locked frequency, it was a great pleasure to have a conversation using a home built transmitter and receiver.

As the receiver was zero beat to my carrier and Sam had tuned to my carrier he sounded excellent right away.

The direct conversion receiver sounds very pleasant, as this one is crystal locked the only adjustment is a 1K pot on the antenna as RF gain - this works just fine as a volume control too.

It's a very happy day here at VK2TPM.


Anonymous said...

Great work, Peter. If you can, why not add a switch on the front panel to switch between the 3.58 MHz crystal and a 3.58 MHz ceramic resonator (for agility).

A 10-160pf variable capacitor could be wired in series with the switch - this would give a few hundred Hz swing with the xtal and tens of kilohertz with the ceramic resonator.

crystal oscillator said...

Thanks for your presentation and I appreciate that!
Keep up your good work. I will come here regularly for news.

Junaid said...

plz help me in this regard
how can i convert wifi signals into rf or rf ino wifi.
as i want to operate my uav from laptop or i can made my uav(helicopter) wifi enabled.
what circuitry should it require?
plz help