wrote:
On Mar 13, 12:02 pm, "Anthony Fremont" wrote:

I believe this is direct conversion and that the crystal should
exactly match the desired station (3581kHz) I want to recieve,
that's right isn't it? Maybe this is close enough? I have to wait
til tonight to see if I can actually hear anything.

Depends on what sort of signal you are trying to receive.

To receive a single our double sideband signal (or, in a very touchy
way, an AM one), you want your direct conversion receiver's local
oscillator exactly on the transmitter frequency.

But to receive a CW signal, you want your local oscillator 700 Hz or
so above or below the transmit frequency. That will cause you to hear
a 700 Hz audio tone for the CW.

Unless I'm mistaken, 3.581 MHz is in the CW portion of the 80 meter
band.

It is, I mistakenly thought they did the 80 meter voice announcement down
there. The voice bulletin is actually on 3990kHz.

Since I have most of what I need (tuning caps, vernier and toroids/wire) I
started looking around at different VFO circuits. I'm trying to find
something that will span from 3500 to 4000kHz and still be fairly simple. I
could then inject this into pin 6 of the 602 and be done with it. :-)

If you can get to 1 KHz below the transmitter, you should be able to
copy CW as 1KHz audio. If you can only get to 1.5 KHz below, you'll
get 1.5 KHz audio... not ideal listening, but probably workable.

Right. I was hoping to be able to "get on the other side" of the signal to
have a second chance at avoiding possible QRM.

On Mar 14, 4:23 pm, "Anthony Fremont" wrote:

If you can get to 1 KHz below the transmitter, you should be able to
copy CW as 1KHz audio. If you can only get to 1.5 KHz below, you'll
get 1.5 KHz audio... not ideal listening, but probably workable.

Right. I was hoping to be able to "get on the other side" of the signal to
have a second chance at avoiding possible QRM.

My guess is the project's original author hadn't planned on that...
most likely, they'd planned on rubbering the crystal only far enough
to get a reasonable audio tone from the RF-LO combination.

Obviously you can get more range out of a VFO, though building nice
VFO's isn't simple.

Even the tuning caps can be a pain. I spent a while as a teenager
knocking alternate plates out of old 365 pf AM broadcast caps to try
to make some suitable for 40 meters - or you can use a series
capacitor. Beware hand capacitance when you go to tune it. Today,
varacter tuning is another option - stable regulated supply and a
multi-turn pot.

Another thing you might do is google the "poundshop" (dollar store)
receiver projects. Those are little KHz-IF varactor tuned auto-
scanning FM radios that people have been modifying into direct
conversion ham band receivers.

wrote:
On Mar 14, 4:23 pm, "Anthony Fremont" wrote:

If you can get to 1 KHz below the transmitter, you should be able to
copy CW as 1KHz audio. If you can only get to 1.5 KHz below, you'll
get 1.5 KHz audio... not ideal listening, but probably workable.

Right. I was hoping to be able to "get on the other side" of the
signal to have a second chance at avoiding possible QRM.

My guess is the project's original author hadn't planned on that...
most likely, they'd planned on rubbering the crystal only far enough
to get a reasonable audio tone from the RF-LO combination.

Yeah, I probably expect too much from it. On a side note, IT WORKS. I can
hear stations, but the noise (man made) is something awful. It really needs
a narrow audio filter.

Obviously you can get more range out of a VFO, though building nice
VFO's isn't simple.

Even the tuning caps can be a pain. I spent a while as a teenager
knocking alternate plates out of old 365 pf AM broadcast caps to try
to make some suitable for 40 meters - or you can use a series
capacitor. Beware hand capacitance when you go to tune it. Today,
varacter tuning is another option - stable regulated supply and a
multi-turn pot.

Another thing you might do is google the "poundshop" (dollar store)
receiver projects. Those are little KHz-IF varactor tuned auto-
scanning FM radios that people have been modifying into direct
conversion ham band receivers.

I found some stuff on those, the look pretty neat. I may have to head to
the dollar store and see what I can find. ;-)