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maco 5-element to a 7
- Thread starter 552fl
- Start date
No..But throwing out the gamma and directly feeding the drivin element is.
No. The extra 11 feet of boom will really be a bugger o deal with in the wind and any ice and will really tax the rotator and support. The extra 2 dB gain is less that half an S-unit in gain. IMHO it is not worth it.
I would call the five element pretty much the "sweet spot" for size versus performance.
Never underestimate how much added force will be put on the rotator when the wind blows on a longer boom. Plan on a bigger rotator if you lengthen it.
Brings to mind the old saying "Torque is cheap".
73
Never underestimate how much added force will be put on the rotator when the wind blows on a longer boom. Plan on a bigger rotator if you lengthen it.
Brings to mind the old saying "Torque is cheap".
73
As in a hair pin match? I am looking for more information about this, if you could point me in the right direction I would be grateful.
DXman
Yes, that's 3100 degrees F. Nine yrs of hard work.
Hair Pin matching system is of course better, but, will it make much difference on 11 meters? I doubt it - but just do like every one else does --- run more power!!!
You cut the driven element in half and add an insulator.Make sure to space it to prevent arcing. Feed it like a dipole. Add a coax choke..ugly balun..to keep the RF out of the coax. Adjust length at antenna.
If you go that way, there are two things to keep in mind. You don't have the option of leaving the balun out unless you're willing to deal with a good deal of CMC coming back down that feed line. You also don't have the ability to adjust the impedance without making compromises to the elements resonant length and or positioning of the elements on the boom to get a good VSWR.
My favorite matching network in terms of performance is the T-Match using no gammas. It's also my least favorite to build and tune correctly. When done right, the pattern off the front of the beam is very symmetrical and the CMC is lower than other matching networks I've used.
With a little work, a 1.1 match from 26-28mhz.
Mustang I tend to agree with you, the idea of splitting the center of the driven element and direct feeding (DF) a yagi beam has merit.
IMO, we should also isolate all the elements from the boom and use good insulators to support each element at the center and above the boom.
Matching is important, but IMO this DF idea can produce much improved symmetry. If so, I think it's likely the antenna currents will not tend to produce the common mode currents on the mast/feed line that typically make for problems.
This DF idea can produce some benefits along with a modest decrease in performance possible. That said however, my models indicate a near doubling of an increase in bandwidth over my traditional gamma fed yagi.
As I note above, my models suggest if we can improve the symmetry in our yagi beam we can gain nearly 1 Mhz in bandwidth at a very low SWR match...with only a modest loss in gain, at resonance.
To me, symmetry is probably more important to a yagi beam antenna in overall performance than having a perfect match.
With three iterations of models, I can see how the symmetry might look and how the DF model performs better in several ways.
1. improved bandwidth from 26 to 28 < 2.00:1 SWR. Sorry Mustang, I don't see 1:1 from 26 to 28 Mhz. Maybe I should check over my model before I post em'.
2. improved performance as I go higher in frequency up to 28 Mhz with my DF'd model without the need for a choke.
3. due to the improved symmetry and the increased bandwidth the DF model shows an SWR lower than 1.50:1 across the entire CB band in the USA where the first two gamma fed models don't appear to come close.
Source of information above:
1. (Marconi's 105CH wM wM 36'a) - a model with a simulated gamma using no choke at the top of the mast. Model has no feed line.
2. (Marconi's 105CH wM wM 36'a) - the same model as #1 above with a choke at the top of the mast. Model has no feed line.
3. (Maco 105C H wDF sM nFL 36') - a model that is direct fed at a split in the driven element. Isolated from the boom and the mast. Model has no feed line. Source of this model, in part, is from Henry's Website.
Models to follow.
2. (Marconi's 105CH wM wM 36'a) - the same model as #1 above with a choke at the top of the mast. Model has no feed line.
3. (Maco 105C H wDF sM nFL 36') - a model that is direct fed at a split in the driven element. Isolated from the boom and the mast. Model has no feed line. Source of this model, in part, is from Henry's Website.
Models to follow.
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If the bandwidth increases then the gain will decrease correct? Splitting the driven element means splitting it at the boom? Just trying to picture it.
STM, you are right...this is the way I understand it and this is what these models indicate.
Your right 1.1 from 26.9-27.5
1.5-2.0 from 26-28
131, maybe you can check out your added 1:1 from 26.9 - 27.5 on the last model's SWR scan I posted below and see if the model is close here too.
Note: when you click on the file at the bottom and the page opens...make sure to click on the button marked "Open With."
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