Influence of the cable length: End fed half wave antenna
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- čas přidán 31. 05. 2021
- I think the EFHW antenna is one of the most recommended antennas for QRP and portable. So at this short video I will show the influence of the coax cable length to an EFHW antenna. It looks like there is an optimum of length.
There will be some videos about Elecraft KX2, Fourty-9er and the Pixi soon.
Dieses Video gibt es auch in Deutsch: • Einfluss des Speisekab... - Věda a technologie
I agree about the coax length. For 20m I use a 5m c/p and 3m coax and it works well and no rf issues. I have found shorter coax and lowering the feedpoint to negatively affect the swr. Having the matching unit ~0.5m off the ground seems to work ok. Good advice about experimenting first - that can save a lot of time. Nice videos👍🏻👍🏻. 73 de Will, M0LGW 👍🏻😊
Very interesting analysis. Good job, thank you.
Interesting. Going by the other stuff I've read about EFHW's & the 49:1 transformer, I did my first tests with a 30ft/10m feedline & no counterpoise at the transformer. Tuning up was easy. I was using a reel of wire that I simply wound back to a length that gave me a resonant point on 20m. ReverseBeacon reports showed that I was getting out across the US to the west with 5W.
. . . Then I took the whole mess inside, hooked the transformer to a chunk of wire hanging in the air from my second story office/shack window. Feed line was at the most three feet (about a meter). Testing at 20W, I got immediate messages on the office computer about RF devices not working. Foolishly ignoring that, I continued t he tests. Then the keying line to the radio (a Xiegu G90) went dead, one side at a time. First the dit side stopped working, then the dah side.
. . . Turns out I had burned up the very tiny, flea-sized 100Ω resistors in the keying line. I'd killed the radio, so to speak. (Repairing that was terrifying for an old man with shaky hands)
. . . Since then I have repaired the radio, added extra bypass capacitors to the keying lines & put a choke on the keying line at the radio.
. . . Now, when I use any EFHW set up, I ALWAYS use a feed line of at least 30ft/10m and put the 49:1 transformer & radiating wire at least that far from me and the radio. And there's a 1:1 current unun at the radio & plenty of clamp on chokes on the keying lines & peripheral cables. I don't want to go through the terror or repairing the radio again.
So, yes, you are right: Test before going out and use a decent enough length of feedline. And always use the current choke at the radio.
73 de W8IJN
I have the same antenna, hut have used different length wires. I use a 50' length of coax and it tunes, great on 80-20 and 10 is 1.8'ish.
Hi,
WSPR showed very poor performance or propagation. Despite the number of spots, all of them have VERY low SNR.
E.g. SNR 6dB means that your signal is 1S unit above the noise level. In your case the best results is 0dB that means that almost no one (except software) was able to receive your Morse Code signal by ears (this we saw with CW beacon).
Also, in additional to SWR, more intersing R/X. Because adding more cable or adding CMC choke you adds more reactance and it should be compensated e.g. by capacitor or inductance.
But anyway, looking on impedance, the best one is third, because it has active 48 Ohms and capacitance can be compensated a little longer coax (or antenna).
The worst is third one, because it has real 65 Ohms and a little inductance.
Thanks for making this. What about the guys who don't use coax at all, just the matching transformer on the back of a BNC, K6ARK does this, so do others.
I have made many EFHW's with the transformer attached to the radio with great success. Depending on transgformer desigh will dictate the need for a counterpoise.
Hello Björn. Have you been able to test the two meter cable with the counter poise?
Interesting…. QRPGUYS also offer the exact same EFHW antenna kit in a smaller package but with a counterpoise nut on the side. It is called QRPGuys Mini 80m-10m No Tune End Fed Half Wave Antenna. Look at it. Exactly the very same circuit in a different presentation. This one comes in a box that offers a little more rain protection. The other one, the green one on your video, doubles as a wire winder and is more eye appealing, but has no rain protection at all. I have both versions but, as strange as it gets, the one in the box works way better than the green one. Have used both without counterpoise. I then added a counterpoise to the one with a box and no change was noticed at all. I was using a 10 meter RF cable. The radiating wire length was exactly as per QRPGUYS table and was perfect match. The same wire was then moved to the green one and didn’t produce the same results. It required a little shortening to match. Same RF cable, same day, same place. Same conditions. Again, same exact circuit. Makes no sense at all. 73, Rob, YS1RS
Hi! Greetings fromUK.
Great video and very useful information.
A quick question about the QRPGUYS antenna board- Is it OK to use in the rain?
Thanks for sharing.
This is a interesting question. I would say it will have some influence to the output impendance of the UnUn. So may be it will result in a bad SWR. I think the best way to know it to test it. Vy 73 de Bjoern, DL2NEP
How many meters of wire does that antenna have?
I use a 6ft coax with choke and have none of the SWR/common mode coax currents you show in this video with the 49:1 end fed halfwave.
really interetsing - can I ask how long is the element pelase?
(I ahve built smae antenna - and having trouble tunning it
I have a serious question. I've learned cokes cause a power loss. In QRP that could be a significant problem. Could You explain any power loss from this set up?
I don’t understand what you mean by “errors on the cable“ in demonstration number two. Please explain further.
Dave K8WPE since 1960
I said "problems with RF on the cable". There are RF current outside the coax cable. This will make trouble on some transceivers. So I connected the small cable containing an RF-choke to the 5m cable. The result is a little bit wors SWR but no RF on the outside of the coax. So the transceiver works fine. 73
Help me please, I have a QCX QRP (not mini version) and an antenna EFHW of QRP Guys like you. But I dont have an antenna analyzer. :-( I want to transmit in 40 meters. How should be the configuration? TG9 NYM.
Can you specify the ferrite core you use on the 2m cable? I'd like to buy one on Amazon but do not know exactly which one to get. Thanks!
I removed that ferrite core out of an 1:9 UnUn i bought long time ago. But I expect it is an FTxxx-43 core. I think it has about 5cm diameter. You can test it. After 7 windings the problems with my QCXmini gone completely. Happy building. Bjoern
@@echopapaqrp8166 What symptoms of RF interference did you have before applying the RF choke? Also, can you clarify how you tested specifically for this noise?
Thank you for providing some direction on the ferrite core specifications. Can you clarify 5cm outer or inner diameter? If you have any additional reasoning to explain why that ferrite core works for the application as well as the reasoning for 7 turns, it would be helpful for an antenna novice like myself and potentially many others.
For example, what is the difference in FT-240-43 and FT114-43? Would both work?
The audience of your videos is newbies like myself, and the more clarification you can offer on these complexities, the more helpful! Thank you sir!
I found the following information to supplement your comments:
FTxxx-43 Common mode Choke
"(Ferrite core) 43 Material is a very good wide band common mode suppression solution in the frequency range from 10 up to 600 MHz. If you use multiple cable turns around the ring core, the suppression will increase while the frequency will decrease."
@@dgkrompholz The problems are strange behaviour at CW keying (some dit and dah missing or too much.) sometimes the QCXmini shows a "G" vor "GPS connected" and the side tone is very noisy and scratchy. If you connect the common mode choke everything is normal. I think there is no special ferite core needed. If you have a bigger one (suitable for your coax cable) try with 5...10 windings. If you have no problems like mentioned above you do not neet a choke. My expirience is that this choke is very useful. Specially on end fed antennas or portable vertical antennas. With an good old dipole you do not need it. Vy 73
I am watching this a year later than my first question. I still don’t know what you mean by “errors on the cable”. Did you have interference in your transceiver? RF feedback? I am still mystified. The SWR was very low and I saw nothing on the analyzer that would bother me. Please give me more information on what the errors were and how they caused you any trouble. I do agree that a common mode choke helps reduce any feedback into your rig and sometimes makes reception better but the “errors”? Also the Chinese knock off with the bad spelling is probably of poor quality (the toroid) so the results might be in error due to that. I have the USA made one from real The QRP Guys and it performs very well for what it is. Dave K8WPE since 1960
how do you calculate the best cable lenght?
You don't need to calculate cable length. Only try & error. As I showed in the video you can easily test this things and find your optimal length. May be something > l/4 should be a good starting point. Best regards, Björn
@@echopapaqrp8166 ok thank you!
It would be interesting to see what effect, if any, counterpoise wires of various lengths might have. DE WA1KLI
Yes, I also think about this.
For me the question is: "Is a counterpoise realy needed?" If yes: Why? The lenght of the active wire is l/2. So this should be all. It seems that there are some effects that need a counterpoise. If you watch my videos carefully you will see that the first videos all have 0,5m wire attached to the BNC-ground. It works fine. But the influence of the feeding cable was also very huge. I think I will do some experiments with the 2m cable and a counterpoise. Then we can see if it helps or not. Vy 73 de Bjoern
Hello, what antenna analyzer do you recomend me? TG9NYM.
I got the "mini 1300" cheap on ebay. So I bought it. I don't know if this analyzer is good or not. It helps to adjust the antennas to the right SWR. So I am happy with the mini 1300. But there are many more. Some does not have the HF bands. Vy 73 de Bjoern, DL2NEP
you are using the chinse clone of the qrpguys end fed
I know that and I mentioned it in one video.
The correct term is counterfeit.
The cheap toroid coils on those cause most of the problems. Replace that or buy the original product for best use.
Hey, I love the videos.... hate the openings....lol. drives me crazy.. 73.
So bad? I will work on it. But I can't say when it will be changed. 73
I see you bought the Chinese knockoff of the qrpguys product. The typo "End Eed" gives it away.
Yes and the "Wava" 😄 👎.
Intro is longer than the video.
I know!