The difference a doublet makes
I had the opportunity to chase a QRP SOTA station on 17 meters a few minutes ago. I thought I would let you hear what I heard. In this video you will see the difference between an OCF dipole, a ZS6BKW multi-band dipole, a Cushcraft R-5 vertical, and my doublet (250 feet of wire, fed in the middle with ladder (“window”) line. I’m using my Yaesu FTdx5000MP.
Technically, open-wire line is the wide-spaced type that many hams build themselves. It is commonly called ladder-line. The window line is still considered as ladder line, as it mimics open-wire line, with only a slight bit more loss. Still, it has significantly less loss than coax. Parallel wire feeders don’t lose as much power in the form of heat as does coaxial cable. Open-wire line is slightly more efficient than window line but less easy to deploy. Both have an efficiency of above 90%, with the open-wire line nearer to 100%. For the few percent of difference, I prefer working with the window line.
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73, de N4HNH
Пікірлер: 17
Thanks your videos for us FTDX 5000 owners are a great resource.
@n4hnhradio
4 жыл бұрын
Thanks Jim! There is so much to learn about the 5K. I’m more impressed every time I sit in front of it.
@n4hnhradio
4 жыл бұрын
Thank you so much, Jim! The 5K is a beast. There are many great radios on the market these days. I have observed that most hams aren't using their radios to their fullest potential. the operating manuals are sometimes unclear. I just thought I would share what I learned from the school of hard knocks, in case it helps others.
Excellent antenna indeed.
Never can have too many Antennas!
@n4hnhradio
3 жыл бұрын
Amen to that!
I’m sold. Need a full legal limit replacement for my efhw and need to move my ham shack toward the center of my house. Reducing noise and longer feed line are big benefits as well.
@n4hnhradio
Жыл бұрын
You might find these videos interesting as well. Watch them in order. kzread.info/dash/bejne/oamG1NlmgsmWkZM.html kzread.info/dash/bejne/io2NmdKCY9rZoLQ.html
My understanding is that ladder line will not radiate. Is that true? Or, do you get some RF in the shack?
@n4hnhradio
3 жыл бұрын
That’s correct, in a perfect installation. My ladder-line runs near a downspout, which is unavoidable. My ladder-line is also near one of the lengths that falls into resonance (approx 57-60 feet). 65 feet is a point of resonance. It can actually act as an antenna, receiving RF radiation from the antenna and feeding it back into to the shack as common-mode current. But ideal lengths, like 40 or 80 feet, weren’t practical in my installation. The center of the antenna is at 45 feet. Coming straight down and into the shack, via the window, and then over to the back of the tuner, took another 12-15 feet. The bands that seem to produce the most common-mode current in my scenario are 15, 30, and 40 meters. For the other bands, I’ve been able to choke the RF by placing ferrite chokes on wiring such as the mouse, the monitor, the mic cable, and the cable between the computer and the radio’s CAT port. I was going to experiment with adding some ladder line to get it closer to 80 feet but 1> I would have to find a place for so much additional line to be routed and 2> the antenna is below a 2:1 SWR across 17 and 20 meters without the tuner, though I sometimes allow the tuner to touch up the SWR a bit. It performs very well on 17 and 20 meters. So, given the performance of this doublet as-is, I just figured I would leave well enough alone. 73, de N4HNH
@izzzzzz6
Жыл бұрын
@@n4hnhradio Avoid 64ft of open wire ladder line at 40M. 42ft-52ft or 73ft-83ft of line is best (+-10ft), at least for 40M around those lengths.
@n4hnhradio
Жыл бұрын
Yes. I’ve seen the charts on that. Mine is in the 50 to 60 foot range, maybe 55. I don’t use mine for 40 normally but it works great at night on 40 for DX. During the day, my ZS6BKW beats the doublet.
What type of lightning protection do you have for your 450 ohm feed line?
@n4hnhradio
10 ай бұрын
The feedline comes to a Balun. I covered that extensively in videos last year, around the Spring time. Those videos are still visible. They haven’t been moved to Patreon. From the Balun to the amplifier/ATU is a 9 ft. run of LMR400. All of my other antennas go to an Alpha-Delta antenna switch. I always leave the switch in the grounded position when I leave the shack. There is an open position on the switch. I unscrew the LMR400 from the back of the amplifier/ATU and connect it to the open position on the antenna switch when lighting approaches. I unplug the power to the radios. The power company will tell you that the only truly reliable protection from lightning is to unplug. I have used the aforementioned technique since 1998 at this location and I’ve experienced no lightening damage. My power company told me that my zip code gets the most lightening of the entire metro area. So, anecdotally, it seems that my method is working.
@n4hnhradio
10 ай бұрын
Back when that video was made, I used a Palstar AT-Auto. It has a built-in Balun so the ladder line came into the shack to the back of the tuner. That tuner failed last year so I started using the auto-tuner that is built into my Elecraft KPA-1500. But it has no connection for ladder line. I installed a 4:1 Balun just inside the window. The ladder line comes to it. 9 feet of LMR400 goes to the back of the Elecraft KPA-1500.
Fine business. 73
Man, you need to turn the radio down some and speak up into the mic so we can hear what you are saying. Kind of hard for the ears to compete between hearing you and null out the radio at the same time.