-
You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
5/8 wave @ 37'
- Thread starter HomerBB
- Start date
@Marconi
I caught an error in what i told you.
I made the ring an overall length of 47". I needed only to bend it back to the vertcal at the upper end if it. Thw bottom end is attached to the aluminum plate by use of a stand-off bolt 1-3/4" above the plate directly beneath the upper end of the coil.
I caught an error in what i told you.
I made the ring an overall length of 47". I needed only to bend it back to the vertcal at the upper end if it. Thw bottom end is attached to the aluminum plate by use of a stand-off bolt 1-3/4" above the plate directly beneath the upper end of the coil.
Ok Homer, if you get a nice wide bandwidth of 2.00:1 or better, then I will redo the model and make it at 27.385 and redo the coil to your corrected dimensions.
As I posted above, my model shows a bandwidth of 1.20:1. Since we have no easy way to verify the model compared to your antenna performance results...then the bandwidth is the only measurement that is easy to calculate in both cases. If that is similar then I would consider the model is close.
The model is reporting gain at a low angle very close to my other models that I have posted of late.
The coil appears to have some bandwidth, but I doubt it will cover 10,11,12 meters without a little modification to the length. So, regardless of whether or not you bent one end or both...are you saying the total wire length is only 47" inches including the leg(s)?
I also found and error in my model. I made the coil wire 0.375" inches in diameter. I went to my garage and checked the dimensions on my Wolf 11_M and the coil has 7.75" inches legs x 0.50" diameter tubing. I changed the diameter but left the legs the same, and the match changed a little so I left the leg length at 8" inches.
So, the only difference is my model reads the match at the feed point, and you probably used a feed line that might show a bit of transformation in the match. My new match now shows R=48.08, X= +0.1581 ohms with SWR = 1.040, and the radiator length is 270.4" inches = 22.5' feet with new maximum gain = 3.74 gain vs. the 3.75 I reported earlier. Note this inductor really works to fix the bad match we see on a 5/8 wave.
See new fixed model below.
As I posted above, my model shows a bandwidth of 1.20:1. Since we have no easy way to verify the model compared to your antenna performance results...then the bandwidth is the only measurement that is easy to calculate in both cases. If that is similar then I would consider the model is close.
The model is reporting gain at a low angle very close to my other models that I have posted of late.
The coil appears to have some bandwidth, but I doubt it will cover 10,11,12 meters without a little modification to the length. So, regardless of whether or not you bent one end or both...are you saying the total wire length is only 47" inches including the leg(s)?
I also found and error in my model. I made the coil wire 0.375" inches in diameter. I went to my garage and checked the dimensions on my Wolf 11_M and the coil has 7.75" inches legs x 0.50" diameter tubing. I changed the diameter but left the legs the same, and the match changed a little so I left the leg length at 8" inches.
So, the only difference is my model reads the match at the feed point, and you probably used a feed line that might show a bit of transformation in the match. My new match now shows R=48.08, X= +0.1581 ohms with SWR = 1.040, and the radiator length is 270.4" inches = 22.5' feet with new maximum gain = 3.74 gain vs. the 3.75 I reported earlier. Note this inductor really works to fix the bad match we see on a 5/8 wave.
See new fixed model below.
Last edited:
Looks good.
I'll get a bandwidtg measurement soon. Maybe in the morning. However, it will be via the long feedline as i widh not to lower the antenna, yet.
Thnx.
I'll get a bandwidtg measurement soon. Maybe in the morning. However, it will be via the long feedline as i widh not to lower the antenna, yet.
Thnx.
After re-reading your dimensions I see that you also posted the following regarding the length.
I got this wrong too. My model for the radiator was set at 22' 1" = 265" inches for the exposed radiator. Sorry, I missed that 10" inches of the 22' 1" being below the radials. This antenna is also similar to the MacoV58 in some respects and I should have known better than try and model that one with a sorta' hidden capacitor in the design.
Sorry, but I tried. You can't rely on my model above to be anywhere near close to your antenna regardless of the BW differences I noted earlier.
I read your last post. Is the BW result from the analyzer or your SWR meter?
Last edited:
Homer, if my model's BW is not even close to your real world results then this suggest to me my model is not accurate. If you would have asked me earlier what I might expect as a BW with your new antenna...I would have said it will probably be in the narrow range...like my model shows.
My modeling of the 5/8 wave goes far back in my modeling experience. However, due to the natural mismatch on a 5/8 wave being bad and thus requiring a matching device...I have never been able to report the bandwidth for any of the 5/8 wave antennas. The SWR is too high without some form of matching add to the model. So, the lack of my being able to model an antenna with a mismatch...prevents the model from reporting the data necessary to show us a typical BW result accurately.
I think DB is the one that could possibly answer this question about the BW and 5/8 wave antennas, confirm or disprove the results I've reported.
That said, however, in my real world experience with my I-10k, I also have found 5/8 wave antennas to show a narrow bandwidth, typically less that 1.2 - 2.0 Mhz.
I have also heard reports from guys with the New SP500 and the Tornado 27 reporting their 5/8 wave showing them a narrow bandwidth too. My model of the Tornado 27 with a multi-coil tuner also shows a bit over 1 MHz bandwidth. Sirio's Manual also shows the bandwidth of 1300KHz or 1.3 MHz for their T-27. So, I remain puzzled at our differences.
Homer, when you got the idea to do this antenna were you aware of anything special in your design that could show us the nice 2.725 MHz bandwidth you report? Or, do you think it is possible the hidden capacitor idea in your design and in the Maco V58 needs to be considered?
Maybe DB also has some thoughts on this too.
In a search on this forum, I find other's reporting narrow BW for their 5/8 wave antennas. Am I missing something more with my model in your design? I posted a close up of the matching device I added. Does that give you an idea of all that I have done, other than raising the radiator 5" inches above the radials in order to make space for the coil? You will notice that the 1" inch empty space from the bottom of the coils to the top does represent an insulator.
My modeling of the 5/8 wave goes far back in my modeling experience. However, due to the natural mismatch on a 5/8 wave being bad and thus requiring a matching device...I have never been able to report the bandwidth for any of the 5/8 wave antennas. The SWR is too high without some form of matching add to the model. So, the lack of my being able to model an antenna with a mismatch...prevents the model from reporting the data necessary to show us a typical BW result accurately.
I think DB is the one that could possibly answer this question about the BW and 5/8 wave antennas, confirm or disprove the results I've reported.
That said, however, in my real world experience with my I-10k, I also have found 5/8 wave antennas to show a narrow bandwidth, typically less that 1.2 - 2.0 Mhz.
I have also heard reports from guys with the New SP500 and the Tornado 27 reporting their 5/8 wave showing them a narrow bandwidth too. My model of the Tornado 27 with a multi-coil tuner also shows a bit over 1 MHz bandwidth. Sirio's Manual also shows the bandwidth of 1300KHz or 1.3 MHz for their T-27. So, I remain puzzled at our differences.
Homer, when you got the idea to do this antenna were you aware of anything special in your design that could show us the nice 2.725 MHz bandwidth you report? Or, do you think it is possible the hidden capacitor idea in your design and in the Maco V58 needs to be considered?
Maybe DB also has some thoughts on this too.
In a search on this forum, I find other's reporting narrow BW for their 5/8 wave antennas. Am I missing something more with my model in your design? I posted a close up of the matching device I added. Does that give you an idea of all that I have done, other than raising the radiator 5" inches above the radials in order to make space for the coil? You will notice that the 1" inch empty space from the bottom of the coils to the top does represent an insulator.
Yes most 5/8 wavelength antennas tend to have a rather narrow bandwidth. This has more to do with the matching system used than anything as 5/8 wavelength antennas don't actually have a natural match on their own. The natural X and R that must be tuned does change a lot in this region, which is a limit for said matching networks.
One thing to consider, however, is this:
We all know feed lines have the effect of making SWR bandwidth wider than it is at the antenna. Homer, what kind of coax did you use and how long was the run?
That isn't to say that that is the only possible reason for such a bandwidth with this type of antenna, the Gainmaster model I made a while back (and I think I remember Marconi duplicating this type of wide bandwidth on this type of antenna) should be similar, and due to an anomaly in the impedance and reactance curves it had near 4 Mhz of bandwidth, just like the real antenna.
The 5/8 wavelength antenna models I have done that include some form of matching include my I-10K and Shockwave Antenna Models, which shows a little over 1 MHz of bandwidth at the antenna, and my linear loading experimental model showed the same, although it has slightly more bandwidth. I have a model that has a matching network that is similar to a Maco antenna, although without the hidden capacitor mentioned above, and it also has a bandwidth that is a little over 1 Mhz. Unfortunately I only have these four models to go by, and they hardly cover every possibility, but they all have consistent results, to the point of being within 0.2 MHz of each other. I have also use the matching network feature built in to 4nec2, and they also have results consistent to the models above, so all of the available evidence says that that is the range of at least most 5/8 wavelength antennas after matching.
From actual measurements on antennas I have seen, SWR curves in some 5/8 wavelength antennas have a pattern where reactance crosses the resonant point three times within the low SWR region of the antenna, producing a result somewhat similar to the wide bandwidth of my Gainmaster model. While I haven't reproduced this with modeling, I would expect that a matching system that would result from this type of reactance pattern could, and likely would, increase SWR bandwidth at least to some extent. That isn't to say that this is what is happening with Homer's antenna, it is just one possibility I have experienced that might explain a wider bandwidth on such an antenna.
The DB
There may be errors due to losses from a long coax - 75'. This coax is RG58. The RG8 I have was too short, as is the LMR400 I have.
When I decided to build the antenna I simply used the bottom ssection I had previously made for anotger antenna. What I did was look at whether other antennas had a vertical element that descended below the radials. I found it was not uncommon, as in the SP500.
Any changes in the antenna BW was neither planned nor anticipated.
When I decided to build the antenna I simply used the bottom ssection I had previously made for anotger antenna. What I did was look at whether other antennas had a vertical element that descended below the radials. I found it was not uncommon, as in the SP500.
Any changes in the antenna BW was neither planned nor anticipated.
Thanks DB.
I agree, but IMO the GM antenna being a center fed 5/8 wave is likely what produces the nice wide bandwidth for a 5/8 wave radiating element. My GM model shows a similar radiated pattern as Sirio shows us on their Website and my model does not include any matching device. The real antenna also proves the wide bandwidth result, and my model supports the idea too.
Whatever is unique with Homer's new antenna design may well be a break thru in one of the limitations for the typical end fed 5/8 wave...and this needs further testing and consideration to see if it is duplicatable.
Homer what was the bandwidth for the original version with the mulit-coil design?
If the old coil produced a similar broadband result then that would seem to me to rule out the idea...it is due to the coil you designed.
Good work Homer and we all thought the GM was the latest evolution in overcoming the bandwidth issues with 5/8 wave antennas...being narrow banded.
I agree, but IMO the GM antenna being a center fed 5/8 wave is likely what produces the nice wide bandwidth for a 5/8 wave radiating element. My GM model shows a similar radiated pattern as Sirio shows us on their Website and my model does not include any matching device. The real antenna also proves the wide bandwidth result, and my model supports the idea too.
Whatever is unique with Homer's new antenna design may well be a break thru in one of the limitations for the typical end fed 5/8 wave...and this needs further testing and consideration to see if it is duplicatable.
Homer what was the bandwidth for the original version with the mulit-coil design?
If the old coil produced a similar broadband result then that would seem to me to rule out the idea...it is due to the coil you designed.
Good work Homer and we all thought the GM was the latest evolution in overcoming the bandwidth issues with 5/8 wave antennas...being narrow banded.
BTW Homer, when I used your 13" inch diameter coil I remade the coil maybe 10 times and I never got close until I changed the frequency to 10 meters. I changed the coil length an inch or two one way and then the other trying to find a sweet spot.
These changes did not include moving the tap points to different locations (segments) on the coil with every design I made. After failing in all this is when I used the dimensions I had for my Wolf .50_M end fed 1/2 wave antenna.
Did you have to change your coil length at all during your tuning process?
These changes did not include moving the tap points to different locations (segments) on the coil with every design I made. After failing in all this is when I used the dimensions I had for my Wolf .50_M end fed 1/2 wave antenna.
Did you have to change your coil length at all during your tuning process?
Last edited:
When I actually duplicated the wide bandwidth that the GM had in a model, it took more than being center fed to get as much bandwidth as the actual antenna had, and involved the manipulation of an anomaly in the reactance/impedance curves. However, that is secondary to this discussion. What I was referencing the Gainmaster for was the possibility that some 5/8 wavelength antennas would have a similar anomaly, possibly caused by the matching system design.
Using average quality RG-58 coax, I am estimating Homer's 2 : 1 measurements on the radio end would be closer to 2.4 : 1 on the antenna end. Lower if the coax is higher than average quality, and higher if it is of lower quality. Their are to many unknowns to say for certain though.
Looking at it the other way, a 2 : 1 SWR would appear to be somewhere between 1.7 and 1.8 on the radio end, and higher if the coax used was better than average, and lower if the coax was worse than average.
The DB
Using average quality RG-58 coax, I am estimating Homer's 2 : 1 measurements on the radio end would be closer to 2.4 : 1 on the antenna end. Lower if the coax is higher than average quality, and higher if it is of lower quality. Their are to many unknowns to say for certain though.
Looking at it the other way, a 2 : 1 SWR would appear to be somewhere between 1.7 and 1.8 on the radio end, and higher if the coax used was better than average, and lower if the coax was worse than average.
The DB
Last edited: