Or, when do automatic tuners make sense over a manual tuner?
I just found a fascinating article in the May 2008 QST ... actually, it was a short response under Technical Correspondence to an article on automatic tuners. But it answered a question I've had for a long time.
One quote that caught my attention: "...typically, the [automatic] tuners have a tough time when coupling to 'short' antennas whose RR (feedline impedance, if you will) is lower than the prescribed 50 ohms."
The author continues, "...you'll note that in the general instance of the longer -- lower frequency -- antennas, where the feed point (Load) Z is below 50 ohms, the automatic tuners are reticent to couple efficiently, whereas if the feed line Z is above 50 ohms, the tuner is efficient."
A couple of things come to mind ... first, in dealing with short vertical antennas, the antenna Z can be very low, hence the need for radials and/or baluns to match closer to 50 ohms.
Second, if your antenna is "short", whether a shortened 160M dipole or a short vertical, with an impedance of less than 50 ohms, you might want to consider using a manual tuner for better matching range.
If your antenna sports a Z close to or even higher than 50 ohms, the automatic tuners can handle the match easier. The antenna design impedance is affected by a combination of antenna length and height above ground.
This does explain why my auto tuner in my KW TS-440 cranks and cranks to match my NVIS antenna (G5RV at 6 feet high) but quickly tunes on my 40 meter doublet at 20 feet high.
One of these days, I'll have to measure what the impedance is on each of these two antennas.
Something to consider ... AR
Saturday, April 18, 2009
Thursday, April 16, 2009
Narrow Band Emergency Messaging System
Also in the April 2008 issue of QST, there was a short mention of the Narrow Band Emergency Messaging System which is based on PSK, RTTY, or MFSK rather than Packet messaging.
NBEMS was developed by Skip Teller, KH6TY, creator of DigiPan and Dave Freese, W1HKJ, creator of the Linux-based Fldigi.
In my estimation, this program suite takes direct aim at the much-touted and expensive Winlink process.
Together, NBEMS package lets you exchange text and small files in several modes using ARQ - Automatic Repeat reQuest. As you may or may not know, ARQ supports checking and resending data to provide error free transmission of data.
Everything is handled through sound card interfaces so no expensive TNC is required.
Fldigi program puts you on the air on RTTY, PSK31, PSK63, PSK125, PSK25 and MFSK. If you want to use the ARQ features, then the Flarq program interfaces with the Fldigi to make it happen.
There is a very active Yahoo Group supporting NBEMS testing on VHF and 30 meters. Good success has been had with communication between VHF FM mobiles even using vertical antennas. This opens up all kinds of possibilities due to the many hams with this equipment.
The programs are available at: w1hkj.com/NBEMS
...AR
NBEMS was developed by Skip Teller, KH6TY, creator of DigiPan and Dave Freese, W1HKJ, creator of the Linux-based Fldigi.
In my estimation, this program suite takes direct aim at the much-touted and expensive Winlink process.
Together, NBEMS package lets you exchange text and small files in several modes using ARQ - Automatic Repeat reQuest. As you may or may not know, ARQ supports checking and resending data to provide error free transmission of data.
Everything is handled through sound card interfaces so no expensive TNC is required.
Fldigi program puts you on the air on RTTY, PSK31, PSK63, PSK125, PSK25 and MFSK. If you want to use the ARQ features, then the Flarq program interfaces with the Fldigi to make it happen.
There is a very active Yahoo Group supporting NBEMS testing on VHF and 30 meters. Good success has been had with communication between VHF FM mobiles even using vertical antennas. This opens up all kinds of possibilities due to the many hams with this equipment.
The programs are available at: w1hkj.com/NBEMS
...AR
Packet Radio for Emergency Messaging - OUTPOST
Outpost creates a screen that resembles an Internet e-mail application. The user doesn't need to be overly familiar with packet radio. You just need to know how to type and click send. Outpost takes care of the rest.
Outpost was covered in the April 2008 issue of QST. It is available at www.outpostpm.org
Outpost was written by Jim Oberhofer, KN6PE. He is a member of the Cupertino, CA ARES group ( www.cupertinoares.org ).
This program provides the following:
This gives a whole different set of programs for using packet radio for emergency messaging.
...AR
Outpost was covered in the April 2008 issue of QST. It is available at www.outpostpm.org
Outpost was written by Jim Oberhofer, KN6PE. He is a member of the Cupertino, CA ARES group ( www.cupertinoares.org ).
This program provides the following:
- Supports all 3 packet message types - Private, NTS, and Bulletins.
- Create messages from imported files, from scratch, or by REPLY or FWD.
- Built-in message form maker. An NTS message form is provided.
- Supports TNCs, AGWPE, and Telnet interfaces.
- Automatic query/posting to BBS based on time.
This gives a whole different set of programs for using packet radio for emergency messaging.
...AR
Monday, April 13, 2009
Packet Radio for Emergency Communications - EcomScs
In the April issue of CQ Magazine there is an article concerning the use of packet radio for Emergency Communications. This is one of several articles I've seen lately on this topic.
These programs are available at the following website:
www.qsl.net/kb2scs
Even though packet use has been relegated mainly to the APRS applications, the use of packet in EmCom is growing.
The EcomScs program can send and receive messages formatted as NTS messages in attachments. The program handles sending and receiving messages when connected to the bulletin board. Keyboard to keyboard communication is supported as well. Any type of file may be sent or received, whether binary or text. It also allows the user to create their own message forms. It will send picture files as attachments. The program does do some optimization of the file.
GateWayScs provides a temporary mailbox to send and receive local packet mail until normal bulletin board services can be set up or restored. It also can be used to provide an internet gateway for packet messages.
The article describes emergency driven uses for both of these programs. This progam pair provides invaluable connectivity during an emergency situation. Well worth more investigation.
...AR
These programs are available at the following website:
www.qsl.net/kb2scs
Even though packet use has been relegated mainly to the APRS applications, the use of packet in EmCom is growing.
The EcomScs program can send and receive messages formatted as NTS messages in attachments. The program handles sending and receiving messages when connected to the bulletin board. Keyboard to keyboard communication is supported as well. Any type of file may be sent or received, whether binary or text. It also allows the user to create their own message forms. It will send picture files as attachments. The program does do some optimization of the file.
GateWayScs provides a temporary mailbox to send and receive local packet mail until normal bulletin board services can be set up or restored. It also can be used to provide an internet gateway for packet messages.
The article describes emergency driven uses for both of these programs. This progam pair provides invaluable connectivity during an emergency situation. Well worth more investigation.
...AR
Wednesday, April 08, 2009
What Are the Odds?
Sometimes, random happenings just amaze me. Here's a recount of the last few online orders I've made over a couple of weeks ...
On March 24th, I ordered a HyGain Vertical Antenna from HyGain. This was about 4 pm on a Tuesday. The order page turned out to be administered by MFJ which surprised me, but I went ahead with the order for the HyGain. (It is the 10M - 80M AV-18VS.)
A week later, on Tuesday March 31 also about 4 pm, I ordered some vitamins from a company located in Redmond, WA.
On Sunday, April 5, I ordered a 46 in. by 60 in. floor mat for the home office from Office Depot. This was about 8:30 pm.
Now, cue the Twilight Zone music ....
The UPS truck pulled up at the house on April 7 about 3 pm and left all 3 packages!!
On March 24th, I ordered a HyGain Vertical Antenna from HyGain. This was about 4 pm on a Tuesday. The order page turned out to be administered by MFJ which surprised me, but I went ahead with the order for the HyGain. (It is the 10M - 80M AV-18VS.)
A week later, on Tuesday March 31 also about 4 pm, I ordered some vitamins from a company located in Redmond, WA.
On Sunday, April 5, I ordered a 46 in. by 60 in. floor mat for the home office from Office Depot. This was about 8:30 pm.
Now, cue the Twilight Zone music ....
The UPS truck pulled up at the house on April 7 about 3 pm and left all 3 packages!!
Friday, April 03, 2009
Lookup SWL Frequencies
The NASWA Shortwave Listening Guide is a really amazing online tool for SWLing!
Take a look at http://www.naswa.net/swlguide/
You can look up what stations are on THIS HOUR so you know where to tune or you can look up programs by content to find out when they are on.
The listing comes up by Time, but can be sorted by the other columns. You can sort by Target and get all the broadcasts aimed at the Americas, or you can sort by Frequency to see where everything is located. In addition, the topic of the program is also given.
I'll be using the "What's on Now?" feature a lot. I like to know what I'm looking for, so this should really help.
Give it a try - I plan to! ... AR
Take a look at http://www.naswa.net/swlguide/
You can look up what stations are on THIS HOUR so you know where to tune or you can look up programs by content to find out when they are on.
The listing comes up by Time, but can be sorted by the other columns. You can sort by Target and get all the broadcasts aimed at the Americas, or you can sort by Frequency to see where everything is located. In addition, the topic of the program is also given.
I'll be using the "What's on Now?" feature a lot. I like to know what I'm looking for, so this should really help.
Give it a try - I plan to! ... AR
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