Robb, I'm also working on models that are isolated for 1/2 and 5/8 wave. I might even do the slanted radials on this topic. I think so far, I'm not seeing much affects with the 1/2 wave models using 24" vs. 1/4 wave radials, it's like the radials don't seem to have much if any effect. That is also similar to what I experienced in real world testing on the A99.
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adding coax lowers SWR reading on the meter?
- Thread starter mr_fx
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Robb, I'm also working on models that are isolated for 1/2 and 5/8 wave. I might even do the slanted radials on this topic. I think so far, I'm not seeing much affects with the 1/2 wave models using 24" vs. 1/4 wave radials, it's like the radials don't seem to have much if any effect. That is also similar to what I experienced in real world testing on the A99.
sorry for the confushion i just used daves 5/8 video as an example of the look of short radials but was talking about a 1/2 wave not a 5/8. you do need longer radials with a 5/8 but what i read a whi;le back showed that only .05 wave was needed for decoupleling a 1/2 wave
I kind of figure that NB, because I started the models for a 1/2 just to see how the radials affected the magnitude for the currents compared to the 5/8 wave. I have been feeling bad, so nothing so far. Maybe tonight or tomorrow.
My feeling is that the end fed 1/2 wave currents will not respond nearly as much as they do on the different setups per radial length, or isolated and not-isolated compared to the 5/8 wave like I posted earlier.
BTW, the forum is acting so bad today, that I might not get this posted even if I get it finished. I just tried to post this message and I lost the connection, and when it returned my text was gone. Luckly I copied the post to my clip board.
The models earlier were all on non-isolated mast, here are the same on isolated masts.
View attachment NB's .625 wave with 8 x 24 and .25w radials on an isolated mast..pdf
Remember however, when I isolate the mast and it shows less current flow, such will not stop the CMC from flowing on the feed line. In such a case, without a choke of some kind, these isolated setups will likely produce currents similar to those posted on the 13th.
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1/2 wave end fed with 1/4 wave radials vs. 5/8 wave
Here are two 1/2 wave models with 1/4 wave radials that are isolated and not. There also are two 5/8 models with 1/4 wave radials to compare how the 1/2 wave is not so affected using isolation or radials. Both 1/2 waves show high current flow and there is little difference between isolated and not isolated.
I found similar results in my limited real life testing of an A99 with/without radials even though I was not able to measure the current distribution per se. I noticed minimal effects from adding radials to this end fed 1/2 wave antenna. The only question I still have about such testing is Bob suggesting that the way I isolated my mast could have been an issue. I isolated using PVC around the mounting portion of the antenna mast, instead of raising the antenna above the mast 4"-6".
This said however, you will note in comparing the 5/8 to the 1/2 wave patterns, that all lobes for the 1/2 wave are virtually the same whether isolated or not, while the 5/8 wave highest lobe for the isolated antenna is notably lower than the antenna that is not isolated.
View attachment NB's idea .50 vs. .625 with .25w radials isolated and not..pdf
Again the feed lines are not included in the models and where isolation and radials seem to mitigate the problems with high current flow, attaching the feed line can provide the necessary current path to ground.
Here are two 1/2 wave models with 1/4 wave radials that are isolated and not. There also are two 5/8 models with 1/4 wave radials to compare how the 1/2 wave is not so affected using isolation or radials. Both 1/2 waves show high current flow and there is little difference between isolated and not isolated.
I found similar results in my limited real life testing of an A99 with/without radials even though I was not able to measure the current distribution per se. I noticed minimal effects from adding radials to this end fed 1/2 wave antenna. The only question I still have about such testing is Bob suggesting that the way I isolated my mast could have been an issue. I isolated using PVC around the mounting portion of the antenna mast, instead of raising the antenna above the mast 4"-6".
This said however, you will note in comparing the 5/8 to the 1/2 wave patterns, that all lobes for the 1/2 wave are virtually the same whether isolated or not, while the 5/8 wave highest lobe for the isolated antenna is notably lower than the antenna that is not isolated.
View attachment NB's idea .50 vs. .625 with .25w radials isolated and not..pdf
Again the feed lines are not included in the models and where isolation and radials seem to mitigate the problems with high current flow, attaching the feed line can provide the necessary current path to ground.
i don't understand why you have significant mast currents in the isolated examples with little current in the radials,
zooming in the models look to be isolated above the radials,
is that just how it looks or are the radials connected to the mast?
are the masts all the same length and connected to ground?
zooming in the models look to be isolated above the radials,
is that just how it looks or are the radials connected to the mast?
are the masts all the same length and connected to ground?
Bob, it has been a few days since I worked on these models, but I think you're right. I made an error on my idea for the bottom of this setup around the radial hub, and that could make some difference to what I posted above.
Hopefully I'm looking at the same model as you are. If so, this was basically the first model, and it was my attempt to duplicate Dave's 1600 setup with short radials that looked to be about 6" below the bottom of his antenna's mounting hub area, the metal part, but without isolation.
As I sit here thinking about your question, I'm also thinking that I should have isolated the mast at the bottom of the radial hub instead of below the antenna mount. When I checked the original isolated model I think you were looking at...I thought maybe I see what you see.
The fix made the model look better in regards to current on the mast and radials, but the primary lobe went down in gain, the secondary lobe went up a bit, and the highest lobe went down a bit. See the overlay attached.
Sorry for the error guys.
Remember, I was just trying to check the currents in this project, and it was ultimately to be checking the currents for an end fed 1/2 wave.
Thanks for your help,
View attachment Bob's fix idea for NB's short radials idea..pdf
All the mast are the same height except for the 4" isolation models, and they are all at "0" elevation which means on the ground.
that looks more like what i expected,
in the first plots with short radials you have the antenna connected to the radials as you do in the last plot with the mast isolated,
the middle plots noted as isolated are not connected to the radials/mast as far as i can see,
EZBOB reports 24" radilas well below the feedpoint of a 5/8 as skycandy
in the first plots with short radials you have the antenna connected to the radials as you do in the last plot with the mast isolated,
the middle plots noted as isolated are not connected to the radials/mast as far as i can see,
EZBOB reports 24" radilas well below the feedpoint of a 5/8 as skycandy
This trick has worked for me for years, using a field strength meter, putting the FS meter against the coax feeding your antenna, you will be able to find a null, cut the coax there an put a coax connector on it, the swr will be the same as what you will see at the base of the antenna, problem solved radio see's a 50 ohm load on that frequency!........KB6HRT
if a feild strenth meter reads voltage not curent then your fedding it at a 1/4 wave point not the 1/2. i dont know but i thought a field strenth meter would read the rf field instead of just voltage or curent so if the high curent point is what it reads because thats where the radiation is hapening then your dialed in at the high voltage point at minimum rf field
if a feild strenth meter reads voltage not curent then your fedding it at a 1/4 wave point not the 1/2. i dont know but i thought a field strenth meter would read the rf field instead of just voltage or curent so if the high curent point is what it reads because thats where the radiation is hapening then your dialed in at the high voltage point at minimum rf field
you do have the concept, however, in this case the FS meter ( commonly called a reflect-ometer) is reading a NULL,................ 0 voltage AND 0 currect. this is 180 degrees on the sine wave (1/2 wl) BACK from the feedpoint,
a null also occurs @ 0 degrees and 360 degrees too.
at the feed point of a dipole theres a curent peak but a voltage null and at thew ends of the dipole its the opoosite but thtas 90 degrees out of phaze not 180 so how can there be a 180 degree null point for both if they are only 90 out of phaze? something has to be high. iether the curent or the voltage
have i? i dont know because i thought they read the high voltage node:blink: wouldnt you need a curent probe to read the high curent node?