Monday, January 30, 2006

2005 Freq. Measurement Test Results

I entered my first ARRL Frequency Measurement Test in November, 2005, as predicted in a previous posting.

My results came back recently:




BandError (Hz)ppm Error
160M1.22-0.66
80M0.590.15
40M-0.69-0.09

On 160M, there was a far stronger signal level than the other bands, but the results are the worst, probably because of mixed propagation paths, unstable ionosphere, etc. On 40M, the signal was so weak I was not sure if I had it at all, amidst all the QRM. Probably this was ground wave propagation.


The full ARRL report is here.

Tuesday, January 24, 2006

Hamlib QST Stray

My little article about hamlib finally came out: QST, Feb., 2006, p. 101.

Dynamic DNS -- letter to QST

Dear Editor:

Carl Ferguson's (W4UOA) article "Remote Control over the Internet" (QST, February, 2006, p. 62) was very informative. There is a lot of unexplored territory in the combination of ham radio and the Internet.

Let me point a cheaper way to set up your own Internet domain. Namely, free! Set up a Dyndns.org account, as Carl says, but select "Dynamic DNS" service. For up to 5 separate computers, you can select a name like callsign.ham-radio-op.org, callsign.dyndns.org, or many others. Because you are establishing a sub-domain instead of a primary domain name, you do not need to purchase the "custom DNS" service. The IP address updating software (such as DirectUpdate) works almost the same either way.

There are several alternative suppliers for "dynamic DNS services". Try an Internet search.

Martin Ewing AA6E
Branford, CT

p.s. A thoroughly modern ARRL could provide this DDNS service for the membership: providing "your-callsign.arrl.net" to point to a home machine or web hosting service.

--
martin.ewing@gmail.com
http://blog.aa6e.net

Wednesday, January 04, 2006

Preliminary Orion "Radar" data

I was working with the Orion, trying to figure out its T/R timing on QSK CW. It turns out the dead time, from end of "key down" to receiver audio output is about 28 msec, by my measurement. The ideal QSK rig has zero dead time, so that the entire interval between key-down times is available for listening. The Orion has lots of DSP things to turn around, or so I suspect.

I did some of these timing checks on the air (low power) just to be sure we had realistic conditions. After finishing, I tuned around to what I could see on the different bands. The bands were dead -- no signals heard on 20 meters and up. Were there echoes tonight? There was nothing audible. But when I set up on 20, this is what I saw.




The horizontal time axis is 10 msec. per division. The frequency is 14.124 MHz, receive BW = 400 Hz, beam heading 110 degrees. Power is 100 W. We are looking at the AUX audio output. AGC is off. We are using the internal keyer set at 20 wpm. The bright horizontal line is the T/R dead time. The time is 0500Z, 4 Jan. 2006.



To confirm that we are seeing something from "the sky", switch the SteppIR to 180 degrees and transmit toward bearing 290 degrees. The return pulse is absent.



To see a little better what is going on, back at bearing 110, decrease the time resolution to 20 msec. per division. Here we see the two dits and the received interval between them. There is a suggestion, after looking at these waveforms for a while, that we are seeing multiple return pulses that are confused with each other after the first visible pulse. (The slope of the "dead zone" is due to AC coupling in the 'scope.)



For comparison, do the same experiment with the same bearing on 15 meters, 21.127 MHz. No effect is visible.

These photos are like a radar "A scope" view. Range increases to the right. What is the minimum detectable range? This is determined by the relatively slow T/R changeover time. The speed of light is about 5.3 msec per 1000 miles. Therefore the minimum range return echo that can be seen is roughly 5300 miles round trip, or 2600 miles down range. The delay we see here is about 35 msec (falling edge to falling edge), or perhaps 3000 miles range.

This echo return was not audible to the ear, and the range is apparently quite a bit shorter than with the pronounced returns I experienced recently with my 21 MHz New Year's contact with ZS6SIG.

Will some radio science emerge here? Stay tuned.

p.s. WWV is reporting the following:
:Product: Geophysical Alert Message wwv.txt
:Issued: 2006 Jan 04 0603 UTC
# Prepared by the US Dept. of Commerce, NOAA, Space Environment Center
#
#          Geophysical Alert Message
#
Solar-terrestrial indices for 03 January follow.
Solar flux 85 and mid-latitude A-index 2.
The mid-latitude K-index at 0600 UTC on 04 January was 1 (06 nT).

No space weather storms were observed for the past 24 hours.

No space weather storms are expected for the next 24 hours.
I.e., very low activity.

Note added (1/8/2006): Radar interpretation requires understanding the systematic delays of the equipment. Further study shows that the Ten-Tec Orion, as a DSP transceiver, has significant "processing delay" in its receive path. In modes that use the SSB demodulation, including CW, the audio output is delayed by up to 14 msec from the RF input. This will alter the range calculation, above.

(5/22/2008): Figures restored.

Monday, January 02, 2006

HF Radio Science + QSK = Radar!

When operating QSK at 15-20 wpm, I am running into echoes of my transmissions. These occur on certain azimuth bearings at certain times of day, most often to the SE, which is over water until hitting S. Africa or Antarctica from here. I've seen this from 20 M to 15 M, at least.

Rarely, I think I've seen long-path echoes that come back to me from the opposite azimuth. (The SteppIR bidirectional mode picks them up.) More often, the return bearing is the same as transmitting. I haven't been able to measure the delay time accurately, but it is roughly 2 dit (element) times at 25 wpm (about 50 msec), indicating a 10,000 mile roundtrip.

It seems to be a real effect. I can get rid of it by changing azimuth or using a dummy load.

My question is whether other ops see this and whether it has been written up anywhere in "ham space". These are not the "long delay echoes" that people have claimed to see. The radio science community does run HF radar to study fluctuations in the ionosphere, and this phenomenon is probably well known to them.

The Orion makes a pretty fair radar set, as it turns out.

Note added (1/8/2006): The "echo" appears to be an example of the more general phenomenon called "backscattering" in which the ionosphere returns a certain amount of power back in the direction of the transmitter. See, for example, "Radio Amateur's Guide to the Ionosphere" by Leo F. McNamara (Krieger, 1994). Backscatter ionograms are one method of probing ionospheric conditions. Ionospheric scattering modes (normally in the forward or near-forward direction) are sometimes used for ham DX communications via non-great-circle routes when the great circle route is not open.

[posted to tentec@contesting.com]

SKN - Straight Key Night 2006

They've been doing it for years, but somehow I didn't participate in "SKN" until Jan. 1, 2006. Straight key night is a kind of ham New Year's celebration sponsored by the ARRL. For 24 hours, beginning at midnight GMT (7 pm EST in the US), this event encourages everyone to work many stations using CW (Morse code) sent by "straight key".

A straight key traditionally is the simple up-and-down telegraph key, well known from the movies. Lately, the definition has been expanded to include mechanical, semiautomatic "bug" type keys like the Vibroplex. Both these keys have largely been replaced by electronic keyers controlled by a key "paddle". An electronic keyer is much easier to use, especially at higher speeds.

Anyway! Straight key night encourages old-fashioned Morse conversations, and it's a lot of fun in a low-key and noncompetitive way.

I had contacts with 12 hams in the course of SKN: KB5IEU, WA7SPY, W6IO, KD5CB, PS8HF, ZS6SIG, AB5VA, WA5ZNU, XE1ELA, W3TMZ, N5KEV, and K8AQM, with time out to host a small New Year's Eve party at our house -- and some sleep.

SKN is old-fashioned, but as I was filling out QSL cards, I came across Leigh WA5ZNU's blog of our contact -- that he had already posted. You can't escape the Web!

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