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Appropriate 40M Crystal Frequencies

Feb 3rd, 10:58

K0WUQ

Joined: Dec 3rd 2012, 11:13
Total Topics: 0
Total Posts: 0
Editor, please feel free to move this to another forum; I just didn't see any forum that talks about what frequency to use for what.

When I got back into Amateur Radio back in 2015, about all I could afford to start out with was a QRP CW rig. I bought and built the Vectronics VEC-1240K, since it would put me in my old 1960s stomping grounds, 40 meters. The 1-watt transmitter came with a 7.040 MHz crystal, and a pair of solder pads for a second crystal, with a handy selector switch. There is also a 365pf variable capacitor which loads the crystal (in series), making it possible to re-tune over a range of about 3KHz (I was amazed to find that this really does work!).

But, here's where it gets sticky. I soon wanted a lot more power, even more than my 1960s 10-watt rigs, so I designed and built a 30-watt amplifier, mostly from junk box and surplus parts I still had lying around. Naturally, I use the QRP transmitter as the exciter (oscillator). Then, when I wanted to start experimenting with modulation, I was sharp enough to know that I needed to be in the Phone part of the band, so I ordered another crystal at 7.195 MHz to put me just inside the phone sector. What I WASN'T sharp enough to know is that the band is (at least by convention) a lot more carefully divided up than I thought!

I now see that on page 1.17 of the ARRL OPERATING MANUAL, there appears Table 1.2, The Considerate Operator's Frequency Guide. It says that 7.040 is used for 'RTTY/Data DX' and that 7.195 falls within the 'D-SSTV' usage area. Recall that all I can do is switch between these frequencies (and vary them slightly with the 'tuning' knob). I really have no idea whom I might be interfering with, nor whether my CQs would ever mean anything, since presumably no one is listening there.

I note that 7.290 in the table is denoted as the 'AM calling frequency', so should I change that second crystal to somewhere above this? The only CW mentioned in the table is the '7.030 QRP CW calling frequency'. What would be a suitable frequency to use for 'full power' (like 30 watts - ha) CW work? (I happen to have a couple of old 4CX250Bs sitting around - someday ... someday ...)

Now, I'm really afraid of either wasting my time on-air or, even worse, stepping on some toes.

Thanks in advance to anyone who can clarify this issue for me!

Larry K0WUQ
Feb 4th, 08:59

W1VT

Super Moderator

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
I think you will need to spend some time listening, as propagation will vary depending on your antennas in location. Someone on the West Coast may hear Asian broadcasters that are inaudible on the Midwest or East Coast. East Coast stations have propagation to Europe that West Coast stations can only dream about.

I know Europe and Asia have local band conventions. I believe there is a 40M FT8 frequency just for JAs to talk to each other locally. Most of us in the USA don't need to know that.

Zak W1VT
ARRL Senior Lab Engineer
Feb 4th, 12:41

K0WUQ

Joined: Dec 3rd 2012, 11:13
Total Topics: 0
Total Posts: 0
Zak -

One of the things that surprises me when I listen in the sectors my rig now uses is that I almost never hear anything local. In the area just above my 'phone band' crystal I will often pick up SSBers conversing, but these are not strong signals and never even seem to have '0' region call signs. On the CW side, I will pick up CQs ans ongoing QSOs, but again not strong signals nor apparently local. This is mostly listening before 8AM, noontime, late afternoon and late night (before ans occasionally after midnight).

You didn't say anything about my stepping-on-toes concern (interfering with customary band use). This is my biggest concern, and the only reason I wonder about using 'better' frequencies. Do you think there's good cause for me to immediately make changes?

Larry K0WUQ
Feb 7th, 09:23

W1VT

Super Moderator

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
The lack of local signals on 40M is a function of propagation and the correlation with with Sunspot activity. We are at the bottom of the sunspot cycle and there isn't any short skip at higher latitudes.
This should change in a few years when we approach another sunspot maximum.

DX activity is transient at the bottom of the solar cycle. Good openings for DXing tend to be few and far between for most stations, though hams with bigger antennas will find them to be more frequent.

Typically the DX stations are the ones who make the rules regarding frequency selection and pileup management. Stations with big signals also have a big say in how frequencies are used.

DX-peditions will often post preferred operating frequencies and DXers will listen on those frequencies while waiting for the bands to open.

Zak W1VT
ARRL Senior Lab Engineer
Feb 7th, 14:51

K0WUQ

Joined: Dec 3rd 2012, 11:13
Total Topics: 0
Total Posts: 0
Zak, thanks again. What I'm beginning to see is that these things are a lot more conditional and not so 'cast in stone' as I'd have thought.

Larry K0WUQ

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