Sunday, December 21, 2008

Morse Runner Progress

Over the past 6 weeks or so, I've been trying to find 30 minutes here and there to spend with Morse Runner. It's a real blast. I've been trying to do each 30 minute run with the same parameters (all the "nasty buttons" - QRN, QRM, QSB, Flutter, and Lids - turned on, 35 WPM speed, and an activity level of 3). My rate (I throw out all the busted QSOs) seems to be improving slightly:

What's most interesting is learning to recognize when I'm about to bust a QSO, and to ask for fills. Previously, I'd just guess, and about 4% of the time I'd blow it. My error rate is a bit lower now, but it's still bigger than I'd like it to be.

I also just cannot deal with pileups when everyone zero beats me. The best technique I've found is to not send a ?, which just makes everyone send on top of each other again, but to wait until someone sends their call again, or to maybe pick out the last few characters of a call sign and call that station.

I also have a hard time with calls in the form prefix/callsign. I've been inactive on HF long enough that I can't deal with anything other than callsign/prefix. I just need to learn it, I guess.

RFI/TVI Baseline and Solutions

RFI/TVI baseline:

I had a few hours to myself yesterday, and spent some time collecting a set of TVI/RFI baseline data: what devices in my home are receiving signals from my station, on what frequencies, and at what severity. I should add that some of the audio/video devices in my house have had some RFI mitigation applied already - I did not remove those mitigation devices. Those mitigation devices are:

- I replaced the long audio speaker leads (zip cord) on our home entertainment system and my son's stereo system with some custom-made twisted-pair speaker leads (2 different color wires + 5 minutes with an electric drill = twisted pair). These speaker leads have a 1-inch-long ferrite core around which the pairs are wound:

The cores are some things I had in my junkbox, so they're made of unknown material. I think they probably came from Weird Stuff, so who knows what they're made of, but they seem to have helped. Before replacing the speaker leads, transmitted CW on 10 meters was clearly audible in the speakers of both our home entertainment system and the stereo in my son's room. Seems like a success.

- A Bencher low-pass filter just past the transceiver in my station. I had no real reason to suspect any sort of problem with harmonics, but the filter was $85 and that's cheap peace of mind for me.

The next day, I did a survey with the following parameters (values used for this test):
  • Input parameters:
    • Antenna (G5RVjr - closest antenna to home electronics equipment in our house)
    • Transmitter power (100w)
    • Mode (CW)
    • Devices:
      • Home Entertainment System:
        • Sony Trinitron 27" CRT-style television
        • Pioneer Receiver
        • Sony DVD player
        • TiVo Series 2 DVR
      • JVC CD/Tuner (in my son's room)
The RFI/TVI problems I have are:
  • 160M: not measured (I currently have no antenna that will load on 160)
  • 80M: no RFI/TVI observed
  • 40M:
    • FM tuner audio disrupted by sent CW
    • When watching DVDs, screen flashes
  • 20M: no RFI/TVI observed
  • 15M:
    • FM tuner audio disrupted by sent CW
  • 10M:
    • FM tuner audio disrupted by sent CW
After recording the baseline data in a spreadsheet, I tried the following:
  • Disconnected the external FM antenna from the receiver, and there was no longer any RFI (nor was there any signal from KQED!). The external FM antenna is a 4-element yagi about 2 feet below the feedpoint of the G5RVjr. Assuming this was some sort of a fundamental overload problem, I dug an old 300-ohm high-pass filter out of my junk box and put that between the 75-ohm transformer (the FM antenna is fed with RG6 coax) and the receiver. Problem solved!
  • Set up to duplicate the DVD interference, and discovered:
    • Disconnecting the DVD player from the TV only reduced the interference slightly
    • Disconnecting the RF input from our cable system made the TVI go away completely.
My best guess is that there's some sort of common-mode coupling coming in on the CATV feedline (it runs very close to the G5RVjr's feedline). So I'll try a common-mode choke once I get some ferrite parts big enough. A small snap-on choke didn't help matters.

So, at this point, unless there are some gremlins I haven't found yet, the only problem I'll have is if someone is watching a DVD and I'm transmitting on 40M with the G5RVjr. That's actually fairly unlikely, given that my droopy radial vertical works better on 40M anyway, and it's never caused any TVI I'm aware of.

So I'm pretty close to being able to declare my own house clean, which is a big confidence-builder for going QRV in contests.

Tuesday, December 16, 2008

TVI: 80 meters

Operating PSK31 tonight on 80 meters, I noticed that there is a very small amount of interference in the form of horizontal lines. This only happens when I transmit on the G5RVjr with more than 25 watts (at 25 w, the lines are just barely discernible; at 100 watts, they are visible but I wouldn't call them annoying. Should be easy to solve...

(It's nice being able to run the shack - which is in the garage - from my laptop via Remote Desktop while sitting in the living room watching TV.)

Saturday, December 13, 2008

Fiberglass Stacking Mast Poles

I found these neat military surplus fiberglass stacking mast sections at Mountain View Surplus. Each one is 4 feet in length, and has a sleeve section of about 5 inches in length that inserts into the next section. Paul, the fellow at the store, tells me they were intended to hold up camouflage.

They're great for holding up all the temporary antennas I've been building. One great thing about them is that the inner diameter of the taper section of some (but not all) the masts I bought exactly matches the outer diameter of the PVC pipe that I used for the antenna bases of my verticals. I have 5 of these mast sections, so it was really simple to elevate the 20 meter vertical I built to 20 feet.

Friday, December 12, 2008

Project: Phased Vertical Array

I've been thinking about the most effective antenna I could build for 40 meters. Since I've been pretty satisfied with the performance of my 40M tree-mounted wire vertical, I wondered if there was some way to get another vertical mounted nearby and use the two as a phased array. Then I ran across these two articles:
(Warning: the N4JTE article has an error in the section where he describes how to calculate the resonance point of the phasing lines. Go to the end of the comments where he describes the correct method).

Both of these use a method of feeding the antennas that's described in the ON4UN Low-Band DXing book called the Christman Feed. The article by Bud, VA7ST, was particularly good in that he mentions an addition that allows the user to not only switch the end-fire direction, but also configure it for broadside operation by feeding both antennas in phase. I've worked Bud on 80 meters in a contest, and if he can hear me, the antenna must work well!

After reading these two articles, I decided to do an experiment and build a two-vertical phased array for 10 meters. Why 10 meters? Two reasons: One, I have enough aluminum tubing and mast to build a couple of 10 meter raised verticals with resonant radials, but erecting a 40 meter vertical will require more thought. And two, the ARRL 10 meter contest is this weekend! I seem to be making a habit of building a new antenna before (or during!) every contest I try.

My thinking is that if I can get this to work, any phasing relay box I build can be made to work on a different band - I just need to construct different phasing lines for it. I did have some concerns that on 10M, the tolerances for the phasing line lengths might be tight, but what the heck.


Phase 1: Cut the 84 and 71-degree phasing lines

I won't go into all the details here since this is described nicely in the N4JTE article. Using that method, I calculated the expected resonant frequency of the 71 and 84 degree phasing lines (they resonate at a higher frequency than 10m, because they're physically shorter by a factor of 71/90 and 84/90). I calculated the expected length of a 1/4 wavelength coax line, adjusted for the velocity factor, cut it about 10% long, and trimmed until my MFJ-259B antenna analyzer showed resonance (minimum reactance, Xs) at the calculated frequencies. Between getting my formulas upside down and getting confused about whether to multiply or divide by the velocity factor, this took me all of Wednesday evening.

Phase 2: Build the Relay Box

A trip to Fry's in Sunnyvale on the way to work the following morning netted me a couple of 12 VDC 10A DPDT relays, a plastic enclosure, a terminal strip for the 12 relay lines, hookup wire, and some long bolts to use to attach the phasing lines and feedline.

Thursday evening, I put the whole contraption together. It actually turned out pretty well (most things I build have a sort of Homer Simpson look to them):

Interior view

Exterior view.

The posts labeled "Power Off" in the bottom of the photo indicate the antenna that leads in phase when no relays are enrgized. The posts to the right are labeled "Power On" and indicate the leading antenna when the end-fire direction relay is energized. The posts on the left are for the feedline from the shack. When the broadside relay (on the right) is energized, both antennas are fed in phase. The 71 degree phasing harness simply connects to each antenna's posts.

By the way, I used the labels "power on" and "power off" because I want it to be easy when I'm installing the thing to make sure the eastward-pointing configuration, which I'll be using the most, is the one the requires no power to be applied to the relays.

The screw terminals on the bottom of the photo are for the relays (common, end-fire relay, broadside relay).

When I build a switch box for the shack, I'll label the switch positions with the true headings for the resulting patterns. Hopefully when I get the 40M array build, those directions will be "east", "west", and "north/south".

Phase 3: Build the Antennas

To begin with, on Thursday evening I modified my 20M vertical by cutting the radials for 10M and shortening the driven element. Then, I constructed a replica.

Antenna base, radial attachment, and feedpoint

The PVC coupling section slides snugly into the end of one of the fiberglass stacking poles I've been getting at Mountain View Surplus. These poles are great! Three sections hold the antenna up 12 feet. Yes, the connection of the feedline to the antenna is not very sturdy - it's just a temporary experiment.

Finally, at 1am I decided I'd better stop building antennas and go to sleep. Here's how the antennas looked in the morning.

Antenna in mast

Friday night after the kids were in bed, I attached my MFJ antenna analyzer to each antenna and tweaked the driven element length for resonance at 28.5 MHz. I got a best reading in the shack of Rs=50and Rx=1 at around 28.5 MHz on each antenna. I did not take measurements at the antennas because it was raining, and while I don't care about getting wet, I don't think the MFJ-259B feels the same way.

Phase 4: Mount Antennas, Attach Phasing Line and Feedline

I was planning to do this right after tuning the antennas, but arrgh, I had gotten so wrapped up in work Friday that I forgot to go to the hardware store and get the correct size nuts for the mounting posts on the phaser box (I managed to buy the wrong size nuts for the bolts I bought).

Well, the 10 meter contest has started, so I'm continuing my tradition of constructing antennas while the contest is going on! However, since (a) it's nighttime, and (b) 10m looks not good for this weekend, there's no big rush. I'll run out to the hardware store tomorrow morning and get the nuts and plug in the relay box.

(Update: I got everything hooked up Saturday morning.)

How'd it Work?

The results were mixed. During the 10M contest, I could hear better on the G5RVjr, but that may have been due to the difference in height between it (25') and the verticals (12'). On the bright side, I did notice about one S-unit difference when switching the end-fire pattern while listening to stations to the east of me. Although conditions were pretty bad for the contest, I did work a couple of stations in Colorado, and of course a bunch of local NCCC members.

So I'd call this a qualified success. Although the overall performance wasn't very exciting, I've got a relay box and in-the-shack phasing control switch that works, and can be used on a similar antenna built for a lower band.

TiVo RFI update

I found a way to stop the RFI coming from my TiVo on 80 meters: unplug the S-Video cable from it! Our TV is connected to the TiVo via the RCA cables, so the S-Video output wasn't being used. Unplugging it from the TiVo solved the problem.

If I actually were using the S-Video output, I would have needed to try to stop it from radiating, but this fix is a bit simpler!

So, if you're experiencing this kind of noise, it might be coming from the S-Video cabling.

Sunday, December 7, 2008

A "go kit" for TVI and RFI?

What sort of things should I have an hand to solve RFI problems? I understand that it's risky installing devices on neighbor's equipment, but I would like to keep some things on hand to solve any problems I might have in my own house, and then can point to them and say "this solved my problem".

So far:
  • A FT-240-43 toroidal core, used to make a common-mode choke for feedlines. Wrap about 10 turns around the core:
  • Having some snap-on cores might be helpful - although they aren't as effective as toroidal cores, they're really easy to install, so having a few of them might help identify which cable is the problem, and you could use a toroidal core then.
  • A high pass filter for 75-ohm CATV coax:
  • A ferrite rod.
  • A low-pass filter on my station wouldn't hurt.
  • What about pickup from speaker lines? In the old days, you'd slap a capacitor across the speaker lines, but my ARRL RFI book suggests that modern audio amps won't like that.
Harris, K9RJ, pointed me to a great article written by Jim Brown, K9YC: A Ham's Guide to RFI, Ferrites, Baluns, and Audio Interfacing

TVI - collecting data

We've got some minor TVI and RFI problems in our house that I'll need to tackle at some point.

Our home entertainment system consists of:
  • A Sony Trinitron 27-inch color television (CRT-type)
  • A Sony DVD player
  • A Pioneer stereo receiver
  • A TiVo Series 2 DVR
  • Conventional (non-digital) cable TV
  • The cable enters the house and goes to a "T" connector. One branch goes to the cable input of the TV, the other goes to our TiVo.
  • During operation on almost any HF band, there is some TVI, but only when the TV is connected to the TiVo. If I switch the TV to its cable TV input, there is no TVI.
  • The interference usually manifests itself by changing the picture to black-and-white, or reducing the color. There may be some crosshatching.
  • Interestingly, this is most pronounced when running PSK-31 and no data is being transmitted. When just keying down for a few seconds in CW mode, there is a brief flash of "color dispearance" and the set seems to recover. I'm not sure why, but transients (key-down, or AFSK shift) seem to be involved.
  • It happens even when I reduce the power output to 5 watts, although it is more pronounced at higher output levels.
  • It's worst on 20 meters, but occurs on at least 80, 40, 20, and 15 meters.
  • The TVI happens even if I am transmitting on the 40m vertical in the front yard.
  • We also saw TVI when I was using a temporary 160M longwire fed from the feedpoint of the 40M vertical.
  • The amateur antenna feedlines (coaxial cable) for the G5RVjr and temporary 20M vertical run underneath the house through the crawlspace, and exit at the back of the house right where the cable TV lines enter.
  • The feedline for the 40M vertical also runs through the crawlspace, but exits on the east side of the house, and comes no closer than 25 feet from the TV/cable lines.
The fact that the TVI is present when using the 40M vertical suggests that the cause isn't feedline radiation, or you'd expect that the TVI would be worse on the antennas at the rear of the property.

I could also swear that the TVI problem got worse when I pulled our old TiVo out of the system (it's been powered off for a while now) and I hooked our new one into the audio/video inputs used by the old one.

My best guesses:
  • The signal is being picked up by a cable connected to the TiVo, and the TiVo is the TVI victim,
  • The TiVo has poor shielding, and is getting overloaded.
  • The signal is being picked up on a cable from the TiVo to the TV
I'll do some experiments with disconnecting cables and see if I can narrow things down. Since the TiVo is also an RFI source, I suspect I'm going to have to expend some effort on it.