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Latest Posts

Topic Author Posted On
HRD/DM780 Not Copying MT63 KJ5YN 4 days, 1 hour ago
Finally, it is critical to have your sound card calibration pretty much perfect for MT63. Follow the instructions that go with your software to check the calibration of your sound card. On receive it's a procedure involving WWV

From what I've read, FLdigi has fewer issues soundcard calibration.

Most of the time, this is only an issue for SSTV and MT63.

The problem is that the oscillator on a soundcard isn't precisely adjusted to the right frequency, as the minor inaccuracy normally isn't an issue. Worst case may be a soundcard with a drifting oscillator--while you can calibrate it, the calibration won't hold over temperature--you may need to use another soundcard.

Zack W1VT
ARRL Senior Lab Engineer

160 meter antenna in smaller space? kb3gxp 1 week ago
An inverted-L is usually the best compromise for a small space on 160M.

Zack Lau W1VT
ARRL Senior Lab Engineer
400 foot inv.vee fed with window line K4PDM 1 week, 3 days ago

Are there directions in which the trap vertical is consistently better than the inverted vee that you find important?

The best solution might be a simple dipole to pick up an important direction. Changing your existing antenna to remove a null in one direction might very well create a problem in another highly desired direction--perhaps on another band.

Propagation does tend to change with the seasons--the best over the pole propagation tends to be around the Spring and Autumnal Equinoxes--right now would normally be pretty good--except to the recent solar flares that wipe out the HF bands. But, it is a lot of work for most hams to move around fixed wire antennas--so they tend to be in the same place for years.

Typically, you want moderate impedances at the antenna tuner output--too low and you get excessive losses in the tuner. Too high results in high voltage issues and possible balun overheating. In theory, swapping the balun for optimum performance makes a lot of sense, but, in practice, I don't know of anyone who does that. One could use a 4:1 balun backwards to step up low impedance loads and improve tuner efficiency.

If you have all band antenna that works well you should consider yourself fortunate--a lot of folks have antenna that falls a bit short of that--failing to work on one or more bands.

Zack Lau W1VT
ARRL Senior Lab Engijneer

Unun or common mode choke kd8azo 1 week, 3 days ago
If you have an antenna analyzer, you could measure the common mode impedance to see if it is high enough to be useful at the operating frequencies.

For single band applications, your original coax choke is usually the best option--you can get very high choking impedances. Ferrite loaded chokes tend to be a compromise, with moderate impedances of several hundered to a thousand ohms over a much wider bandwidth.

There are some good ferrite designs--they usually involve large toroids and winding turns to get a lot of choking impedance--you can't get that by slipping a few beads over some coax.
Here is a discussion "what is an unun?" that may help.

The good common mode rejection of a balun allows it to be used as common mode choke. But, an unun may or may not have useful common mode rejection, so the only way to know is to measure it or trust the recommendation of the manufacturer.

Zack Lau W1VT
ARRL Senior Lab Engineer
Unun or common mode choke kd8azo 1 week, 4 days ago

The terminology folks use is quite confusing. A "unun" is normally an impedance transformer, with unbalanced input and unbalanced output. Typically the idea is to go from one impedance to another. But, some folks do use the term 1:1 unun to mean an isolation transformer, like 600 to 600 ohm transformers used in audio circuits. While you could have magnetic coupling and some degree of choking action, you could also have a 1:1 transformer with the shields tied together, resulting in no choking action whatsoever. But, such a device would provide DC isolation, while shunting any static charge to ground.

Zack Lau W1VT
ARRL Senior Lab Engineer

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