ฝัง
- เผยแพร่เมื่อ 10 เม.ย. 2024
- Rudy Severns is an acknowledged leading authority on the impact and importance of ground radials to vertical HF antennas. Even he was surprised by their lack of impact on half-wave verticals.
Let's see what he discovered and prove that NOT ALL VERTICALS NEED RADIALS!
Connect with my channel by subscribing, commenting and drop me a line: TimG5TM@icloud.com
73
Tim - วิทยาศาสตร์และเทคโนโลยี
Good video. One way to look at the quarter wave vs halfwave situation is this:
Roughly the impedance of a dipole is 75 ohms and a quarter wave vertical is half that or 37 ohms.
If the single ground rod is 37 ohms ( it could be more or less but let’s use 37 for the example) then the power spilts evenly between the antenna and ground loss. The current is the same in the antenna as in the ground loss. The power is always current squared times the real resistance. With the same R value in the antenna and the load there will be equal power in each, regardless of the power supplied. That’s a 3dB power loss. With a halfwave the impedance at the end is very high. Let’s use 3700 ohms as a guess. It may be more or less but that’s a good estimate. Again the current is the same in the 3700 ohm antenna and in the 37 ohm ground loss. Let’s assume the current is 0.5 amps. In the antenna we have 925 watts and in the ground we have 18.5 watts lost. That’s almost nothing in terms of dB! So with a supplied power of 943.5 watts we lose only 18.5 watts. If we could reduce the ground loss resistance we could only ever gain the 18.5 watts in the half wave case. In the quarter wave case we can never gain back more than what we lost which was half of out supplied power. That would be only 3 dB in the perfect case of zero ohms ground loss or perfect ground! Now if the ground loss was more or less than 37 ohms the results would be slightly different but most likely not by too much. I think this logic also supports your and Rudy’s results.
Great info - thanks!
Great explanation, Tim, and also confirms what I have observed.
Excellent!
Thanks for sharing, always a interesting subject.
I only know when i used 32 10m long radials i got long haul dx some days, with 300 10m long radials i get long haul dx every day, and people say they have no room for radials, i have always found room, even in very small gardens. Some times on the air results differ to pc results. For me, the right band and timing on the greyline is the main thing. Big amps and big ants will not always give big dx, as seen in my qrz log.
Good luck tim, 73 zl3xdj.
Nice one Brian!
Very interesting and very clear as always. Thank you
Very welcome!
Excellent video Tim, well explained. Cheers 👍
Thanks Kevan!
Well done Tim. Very interesting.
Thank you!
Great explanation!
Thanks Mike!
Cheers Tim , very interesting . I dont have any room for radials here just a couple of ground rods .
There is always room for radials.
Ah I see. If the vertical is between a 3/8 and 3/4 wave you’ll not need them so much
Thanks Tim, another helpful video
Glad it was helpful! 73
nice job Tim. now with multi band end fed half wave. it is half wave at lowest frequency. like 40/20/15/10 meter one. get on higher frequency bands the current at the feed points starts to go up again. counter poise or using the outside of the shield work more. Explains why some bands can have RF coming back to radio. And like 40 meters good. so I always choke. where the choke is depends on counterpoise or not. now on 5/8 wave and 3/4 wave the current comes back up again and Radials come in to play again. a half wave is where the current dip is. cheers from NY,USA
Good info!
Interesting video and a good explanation of this subject!
Thanks!
OK Tim... Mind Officially Blown 😲
Ha!
Thank you Tim. I found the video interesting. It removed some ‘fog’ from my low level technical understanding. Also like the sweater😁. Best regards, phil.
Glad it was helpful Phil!
Very good vid! 👍🇨🇮
Thanks!!
Never use radials and probably never will (the wife is very defensive of her garden !). The odd ground spike has to do. 73 M7BLC
the question you have to ask is who is in charge?
My video on hidden vertical ant with radials is for small gardens and wives hi
The ground rod definitely works. How well depends on many factors, such as what the ground is composed of where the ground rod is driven and what the ground is out away from the vertical. Obviously most single ground rods have a certain amount of ground resistance and that can be reduced with a few radials. The question is how much and can you really tell? If a few radials help by 3 dB it will be very hard to tell. If they help by 10 dB then yes that’s very significant but still only about 2 S-units. My 160 vertical is actually an inverted L about 3/8 long have had almost the same results with from zero to 3 or so radials over 50 years. I even got 160 DXCC with 3 or less radials. In the 70’s and early 80’ have had some pretty high scores in 160 meter contests with no radials as well as with a few radials. So yes a single ground rod can certainly work! Would I put out a few radials if I could afford the time, money and effort? Yes, I probably would. Would it be a noticeable improvement? Maybe, but I doubt it. Right now I have two radials and worked 615 stations in 2019 ARRL 160 contest the year I put it up at my present location. In 2014 I worked 755 stations with no radials. The year before that (2013) I worked 827 contacts in 27 countries during the CQ160 contest with it and two radials. So I would say the results speak for themselves, you can do pretty good with no radials ( just an 8 ft ground rod) or just a few radials even on 160 meters!
I would be interested in a video on the sea/salt water and the effect that this gives good propagation.Not sure if you have covered this before.
I have done but I’ll revisit
As a person that really doesnt understand antenna theory, I just went ahead and put as many radials as I could on my 6btv, i found that matching improved on adding more radials (not counterpoises). I've seen people use a btv without radials elevated and a few resonant counterpoises for each band, which kept the antenna resonant and also performed really well. TLDR, based on my experience, adding the radials help the antenna, but doesnt need them, and as other have proven, having a good counterpoise cut to frequency can be used as an alternative. Today my 6btv is only used for WSPR, and I absoutely love how well it does on 20 microwatts of power - i get fantastic propergation results with real-time data ! As ever Tim, a brilliant video, i really enjoy learning from you !
Thanks Al! Every day is a day of discovery in this hobby 73
They do when you lift them above the ground on 65+ towers especially in the 24-88mhz vhf low band range
Its call ground affect.
Most these hf antennas are so low to physical ground it lowers theres resonant point ,once you lift them up in the air on a tower ,all that changes in my control tests
For line of sight operation
Whats happening at ground level is totally different to whats happening on a very high miunted tower ,but thats missing in these tests is "ground affect"
All antenna vertical when lifted above the optimum point require ground radials in control tests to optimise them.
Sitting them close to the ground floor ,yes you'll notice ground radials not needed ,i think this factor is not being put in the equation regarding "ground affect"
I dont use pc models due to this extra factor,i use pratical tests in controlled ways.
At the end of the day most hf users tend to be doing skywave communications rather than line of sight unless on the upper part of hf/vhf low side where its more relivent so ground rafials and mounted low to the ground is just as effective for hf skywave comms.
I think i commented before on Channel regarding J poles needs ground radials even though its a 1/2 shunt feed with 1/4wave stub match pin,
In tests J pole with three radials added,isolated from mast ,lifted 65ft above ground performance was much improved no rf currents on outer of coax feed with a balance 1:1 fully dc isolated rf transformer (not coax feed directly as its a balanced antenna feed)
Radials actual improved performance of vertical j pole
Once it was mounted on a very high mast.
If mounted low to earth ground radials did nothing and lowered the resonant point of the j pole ,that what ground affect does to the antenna system.
Id like to see somebody try mounting that cushcraft antenna on a 100ft mast (isolated to mast to avoid dc ground looping ),then do a data test of ground radials vs non ground radials on hf verticals think results maybe different ??
Im unsure if these modelling softwares take "ground affect" into considerations why they could be other variables affecting the theiry data vs practical data ??
Maybe they do ?
Interesting stuff 🤔
Hi Tim
Thanks for the video. In your videos on verticals, you reference the gain at 5 deg angle and not the normal method of max gain at angle xx deg. Is there a reason you use this method? Just curious.
Do you know what impact the use of ground rods will have with fewer radials?
73 M0HYY
Hi there - 5 degrees is the angle I have chosen based upon the fact that true long haul DX has been shown by the ARRL to arrive at this low an angle, in other words, it's a tough elevation angle for an antenna to do well for DX and hence a useful benchmark. Ground rods - not as good in terms of providing the mirror effect which is needed compared with a good bed of radials when using a quarter-wave or shorter length antenna. 73
This was good. I imagine its not so simple with the multiband end fed half waves that are popular, when using on bands that aren't half wave? Or maybe thats becasue these antennas aren't usually used with that much power?
It's still the same as you're feeding at the high impedance point for a wire which is still resonant. You don't have the high current part near the ground for any of the bands.
Any band where the antenna is fed away fro m high current will need fewer radials - so in the case of efhw this would apply to the half wave plus its harmonically related bands. 73
Interesting. I must admit the thing that puts me off using vertical antennas is the need for a radial field. Obviously a half wave on 40 or even 20 gets pretty tall, 20 or 10m. If I set a half wave up as a inverted L however, would it still have a decent amount of low angle radiation? Say a 7.5m vertical section in both cases and the rest horizontal?
I’ll model it and do a video I think
Cool that would be really useful Tim 😊
Hello Tim,
I use mmana-gal to modeling 1/4 GP and vertical efhw, and find that 1/4 GP's gain is better than vertical efhw, but that's goes against common perception. What's wrong with that?
73
How high off the ground was the end fed hw?
@@timg5tm941 I use the default high 0 as the 1/4 GP