Tech Net Notes March 27, 2009

In the above diagram, the interface device, RigBlaster, is pictured in the middle toward the bottom (where the microphone is plugged in). This came from wb5mxo, Guy, via ke5lep, Stan. Thanks to both!

PSK31

The topic for the March 27th edition of the Tech Net was PSK31. We were lucky to have Guy, wb5mxo, sit in and be our "Elmer".

To start off, Guy gave us a brief summary of what PSK31 is: He compared it to teletype over the ham frequencies. Typically, in today's world, four items are needed to send and receive in the PSK31 mode:
1. A radio transceiver
2. A computer
3. In interface device between the two
4. A program for the computer

Since most of us have computers and radios, usually all we need is the interface device and the program. The interface device that Guy likes is the "RigBlaster", but Guy advised us that there are many available that will work and some you can build for yourself.

Once you have the interface device, you just need software. Guy mentioned here that there is a ton of software available, some free, some for sale. He said that much of the free software works just fine.

One issue that came up while in QSO with w5ydl, Dan, was that he had heard that even when the bands are dead, PSK31 gets through. So that even in poor conditions contacts can often be made. Guy, more or less, confirmed that by saying that there is a drop off at night on some of the bands, but daytime contacts are usually possible and often abundant.

In additon Guy mentioned that a lot of information can be found regarding PSK31 on wm2u's page at http://www.qsl.net/wm2u/psk31.html

Not only does wm2u describe how PSK31 works, but he has schematics for interface devices and mentions the software and other products available to make contacting easier. In addition, he has a lot information on contesting, if you're in to that sort of thing (as many PSK31'ers are!).

Also Guy furnished another link that has info on PSK31. It is http://www.mymorninglight.org/ham/psk.htm

Guy made a particular point in driving home two important issues.
1. Don't over-modulate your signal. That's a big no-no in the world of PSK31 in that is uses more bandwidth that is needed and practical, and it interferes with other PSK31 signals. You just don't need to do it, and it botches things up for others.
2. PSK31 is used on specific frequencies on each band on upper sideband only.

w5okl, Richie, related that he had downloaded some free PSK31 software and found a website (somewhere in Europe) that allows you to operate a receiver and listen in on PSK31 traffic. He was able to get a "taste" of this mode of communication without hooking up an interface or even using his radio. It will be necessary to look around internet for the site, but it turned out to be a great way to check things out.

kc5rbh, Jeff, asked if you can do this as licensed only as a Technician. Guy said that it is possible but, practically speaking, the bulk of the PSK31 traffic will be found in the General class frequencies.

w5okl, Richie, provided the following three address to sites that he has visited to "listen in" and control the radio in the PSK31 mode.

http://websdr.ewi.utwente.nl:8901/

http://www.globaltuners.com/

http://www.remotehams.com/

Welcome To the Tulsa Tech Net Blog

NOTE: THANKS TO AD5PE, JAY, FOR SENDING THE PIC OF THIS ANTENNA. TOWER HEIGHT IS 330 FT. THE 80M BEAMS ARE AT 300 FT. AND THE 160M AT 270 FT. TOTAL WEIGHT IS 80,000 LBS. THE 160M IS 3 ELEMENTS, 12.9 dBi GAIN, 26 DEGREE TAKE OFF ANGLE. THE 80M IS 5 ELEMENTS, 15.7 dBi GAIN, 12 DEGREE TAKE OFF ANGLE. FRONT TO BACK RATIO FOR THE 160M IS 20-30 dB AND 20 dB FOR THE 80M.



The purpose of this blog is to support and promote the 2 meter Tech Net hosted by Broken Arrow Amateur Radio Club's w5bbs repeater on 146.910 on the second Wednesday of the month and Tulsa Amateur Radio Club's w5ias repeater on 145.110, and 443.850 and the linked system, on the last Friday of the month.

The purpose of the Tech Net is to focus discussion of technical issues related to Amateur Radio. A big part of that is to provide a forum in which inexperienced (or less experienced) Amateur Radio operators may ask questions and thereby receive advice.

So if you have a question that you’ve been dying to get an answer to, you can do a “shout out” on Tech Net Night. Or feel free to leave us a question/comment on this blog in any one of the posts.

Tech Net Notes March 11, 2009

The net started with a query that wb5vst, Ben, relayed to me on the March 10th RACES Net. He was interested in knowing how to go about hooking up several radios to the same speaker.

With four or so radios in his car and speaker space sparse, having the radios share a speaker would help him manage the available space. What he wants is the ability for one speaker to carry the signals from four radios all at the same time (as if you have four radios on). So a switched speaker system would not necessarily work.

On the RACES Net, kd5und, Travis, suggested a mini-mixing board. A mixing board would tend to isolate the signals from each other and send them to one speaker output.

To start things off on the Tech Net, ke5yoo, Mike, relayed some information he discovered that related to the last Tech Net on February 27th, regarding coax. There was an issue of how to use various types of coax. Mike mentioned that RG58 is not a very good coax to use. It's only good for about 150 watts of power on VHF. In addition, Mike told us that as the frequency goes down, all coax types tend to work better.

ke5zol, Casey, checked in and had a question about the performance of his station. He said that yesterday evening, he copied the RCWA Net quite well, but could not make it in from about 31st and Harvard. He is talking on 10 watts with a magnet mount antenna on a piece of sheet metal in his garage.

kc5wsi, Ray, replied that Casey's equipment performance was understandable and that it is really performing well. Getting into the RCWA repeater with that set up, that far away, is not likely. In fact, Casey is doing well to get into the BA repeater as well as he is. ke5omv, Don, agreed.

ae5ft, Gene, related to Casey that he had a similar set-up when he placed an ultra-light MFJ magnet-mount antenna upside-down on his ceiling vent. Gene went on to mention that with that set-up, at his location, he was able to get into all of the Tulsa area repeaters.

ae5fa, Rob, (regarding 4 radios/1 speaker) suggested that installing a 4 to 8 ohm resistor on the signal side of the audio line coming out of each radio and hooking into the speaker with the return lines (or shield) wired in common and to the shield side of the speaker may work to keep signals from back-feeding into the other radios.

ke5wsu, James, suggested using diodes instead of resitors.

ae4fa, Rob, mentioned that diodes would just "clip" the audio and it would not work well.

kb5vdb, Ron, said that he found a device that you can use to hook up 6 radios to one speaker in the AES catalog, but that it may not allow you to listen to all of the radios at once. The part number is NCS 3220.

wx5lib, Matt, said that he has used a commercially available product to hook up four radios to one speaker in emergency vehicles. It is called a 4-channel combiner amplifier. The website for that is: http://www.fleetradioproducts.com/htm/model301b.htm

kb5vdb, Ron mentioned that you could re-wire a quadrophonic headphone to allow for a 4-input headset.

kc5wsi, Ray, said he found the four into one device from AES and it is called an interface kit with catalog numbers 3240 and 3230.

kc5uoq, Larry, announced the Storm-spotter training in Claremore for March 17th.

Tech Net Notes February 27, 2009

The theme for the February 27, 2009 edition of the Tulsa Tech Net was coax. As most of us have found out by now, there are a lot of varieties of coax out there. Big coax, little coax, medium coax, stiff coax, flexible coax, and stranded vs. solid center conductor. (not to mention the electrical characteristics variations) Some coax jackets are more durable than others. What we would like to know is, "What kind of coax do you use?" What problems have you encountered? What works best? What is your coaxial philosophy?

aa5ss, Glenn, said that he didn't have very good luck on one of his two meter antenna installations using coax. He said it was too lossy. He said that he was able to make some twin-lead work better for the installation of the antenna in his tree.

ke5lep, Stan, had a question, "What works well for jumpers? Big coax is cumbersome; small coax is lossy. Plus, it's understood that the more connections, the more the loss. What is the recommended size and type of coax between switches, meters, equipment, and antennas?"

ki6und, James, mentioned that using equivalent products would be best, in that the entire transmission line will take on the characteristics of the least common denominator, or "weakest link".

kd5njr, Scott, said that a good rule of thumb is that each connector will cost about .2db a piece. He said he agreed with the "weakest link" comment.

kd5vsf, Terry added, "Ground your system with heavy wire to a good ground. Check your specs for the frequency you'll be using most. One of the best instruments for checking things is the MFJ antenna analyzer. Also get good reference material, such as those publications from ARRL."

kd5njr, Scott, came back in and said that the Belden 9913 (or compatible) cable is a good type for jumpers.

ki6und, James, followed with another question, "Is there a way to negate the loss from a connector?"

kb5vdb, Ron, had to say, "Get the best connector you can get. A lot of the loss is relative to the frequency you are using. In some instances you can reduce loss by matching the connector with the frequency you'll be on."

kd5njr, Scott said "...just keep an eye on your connectors. Keep them clean. Use a light electronics cleaner. Keep them clean and free of debris. The worst thing you can do is splice your coax. LM400 is tough to beat."

ke5y00, Mike, says, "As far as coax goes, I just use what I have. As long as you keep it short, you can get away with a lot. I try to keep my length down."

kb5vdb, Ron, added, "RG8 is a military designation. There are several companies that manufacture it...just because it says "RG8" does not necessarily mean that it meets stringent operational specifications. There are a few quality companies out there that manufacture good products, such as Belden and LMR."

kd5vsf, Terry, said, "Keep an eye on that RG59, that can be a bad mismatch on an HT."

kd5njr, Scott said that compared to RG8, RG6 is better for antennas, loss-wise, even though it is 75-ohm and a mismatch. If you have a lot of RG59, look up "1/4 wave transformer" on the internet, for ways to use it.

w5taz, Dave said, "When they talk about balums, there is a big impedence, but when you're talking about the difference between 50 and 75 ohms, there's not that much difference."