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SW, looks like i need to learn a bit more about this, and this might be a good opportunity for that.
i used to think that the reason a fiberglass "102in whip" was actually 96" long was because it used copper as the radiator instead of stainless steel, and that because copper was a better conductor than SS, the length was shorter.
jazzsinger enlightened me to the idea that it was the fiberglass surrounding the copper wire that allowed for the shorter length.
is this the concept that you are referring to when you speak about the "radome" surrounding the radiating element?
if so, my question is, wouldnt the SWR fluctuate in high winds when the antenna is flapping back and forth?
i would think that if the radiator's position inside the fiberglass shell was of great significance, that sirio would have added some insulators that keep the coax centered in the fiberglass shell.
if you could elaborate a bit on this subject as it relates to the gain master i would very much appreciate it.
LC
i used to think that the reason a fiberglass "102in whip" was actually 96" long was because it used copper as the radiator instead of stainless steel, and that because copper was a better conductor than SS, the length was shorter.
jazzsinger enlightened me to the idea that it was the fiberglass surrounding the copper wire that allowed for the shorter length.
is this the concept that you are referring to when you speak about the "radome" surrounding the radiating element?
if so, my question is, wouldnt the SWR fluctuate in high winds when the antenna is flapping back and forth?
i would think that if the radiator's position inside the fiberglass shell was of great significance, that sirio would have added some insulators that keep the coax centered in the fiberglass shell.
if you could elaborate a bit on this subject as it relates to the gain master i would very much appreciate it.
LC
i know this is slightly of topic but i never really understood why the antron 99 and imax 2000 antennas have the full radiator lenght wire inside ? as you guys rightly say the vf should have some affect on the lenght of wire? and its in fibreglass tubes! back on topic lol. i think the only way to really know how the gain master reacts to changeing its internals is to just go out and buy one of the chambers that they use for testing
the choke is a combination of the necessary length at some inside vf to get the proper effect to the matching and phazing, and the inductance of the coil the shield of the coax makes. i think its about 3/8 wave inside which would finish the full wave.
maybe thats something those strange coax matching stubs inside need to phaze right
does anybody know what the red coax is? rg-142?
its a intresting antenna allright. mines going to use tubing and a wilson stinger for the top half
maybe thats something those strange coax matching stubs inside need to phaze right
does anybody know what the red coax is? rg-142?
its a intresting antenna allright. mines going to use tubing and a wilson stinger for the top half
Intersted!
Hi, just wondering is this thread still alive? I was curious as I have recently built a HB GM with details I was given by an antenna homebrewer in Portugal incl all the maths (which I let the xyl sort out as she does maths as a hobby and yes I think its sad aswell) the build came out well and the antenna held vertical outside an 8m FG fishing pole does perform well, one big problem! it is resonant on the 12 meter band with a swr of 1.2? being licenced I was able to test it and was impressed but no matter what I do I cannot pull it into the 10 or 11 meter bands, the ugly ballun at the base makes no difference if its 8 turns or 4 turns on my former which I have used before and all the coax calculations were correct with the right VF rating used, I have tried various top section changes and all failed.
I am stummped with this one? any further development out there would be interesting and helpfull.
Phil
Hi, just wondering is this thread still alive? I was curious as I have recently built a HB GM with details I was given by an antenna homebrewer in Portugal incl all the maths (which I let the xyl sort out as she does maths as a hobby and yes I think its sad aswell) the build came out well and the antenna held vertical outside an 8m FG fishing pole does perform well, one big problem! it is resonant on the 12 meter band with a swr of 1.2? being licenced I was able to test it and was impressed but no matter what I do I cannot pull it into the 10 or 11 meter bands, the ugly ballun at the base makes no difference if its 8 turns or 4 turns on my former which I have used before and all the coax calculations were correct with the right VF rating used, I have tried various top section changes and all failed.
I am stummped with this one? any further development out there would be interesting and helpfull.
Phil
Phil, did you use a capacitor at the end of the coax to handle the reactance? Without a cap in the mix, the antenna would likely resonate well below CB 11 meters.
HB GM
HI Marconi, yes I used one of the possible coax variants which came with the plans which was 15cm of RG58 for the recomended 15pf were the real GM uses 9cm of RG303 for the same 15pf, after sending to this thread I took the coax cap off and put it on my new L/C meter and oh dear it reads 32pf which I cant figure out as others have used 15cm of RG58 with good results?
Going to try and fabricate a closer value cap out of other scrap coax lying about to see how it works.
73
Your therory looks good so thanks all the same.
Phil
HI Marconi, yes I used one of the possible coax variants which came with the plans which was 15cm of RG58 for the recomended 15pf were the real GM uses 9cm of RG303 for the same 15pf, after sending to this thread I took the coax cap off and put it on my new L/C meter and oh dear it reads 32pf which I cant figure out as others have used 15cm of RG58 with good results?
Going to try and fabricate a closer value cap out of other scrap coax lying about to see how it works.
73
Your therory looks good so thanks all the same.
Phil
Please post all the math here, if possible.
9cm of RG303 = 29.5% of 29.4pf = 8.7pf, not 15pf.
There are two things going on with the choke coil coax, both external inductance acting as a cmc choke, and internal electrical length acting as part of the overall tuning/matching to a 50Ω load.
The number of turns of the ~2.8" choke is 16, if ~66% it's ~1/2 wave @ 27.7mhz internally electrically, but I have no idea what the vf is of the shield casing, but that is also important since it's the shield which is forming the choke.
If ~95% vf then 16 x ~2.8" = about 141" or exactly 1/3 wavelength @ 27.725mhz (center of European CB band?) - a truly non-resonant & high impedance length, but what's the inductance made by the coil?
For that we would need to know the electrical length of the shield beneath the medium of the casing which offers some unknown velocity factor.
I sure wish Sirio would post the secrets of the Gainmaster on this forum!
Please post all the math here, if possible.
9cm of RG303 = 29.5% of 29.4pf = 8.7pf, not 15pf.
There are two things going on with the choke coil coax, both external inductance acting as a cmc choke, and internal electrical length acting as part of the overall tuning/matching to a 50Ω load.
The number of turns of the ~2.8" choke is 16, if ~66% it's ~1/2 wave @ 27.7mhz internally electrically, but I have no idea what the vf is of the shield casing, but that is also important since it's the shield which is forming the choke.
If ~95% vf then 16 x ~2.8" = about 141" or exactly 1/3 wavelength @ 27.725mhz (center of European CB band?) - a truly non-resonant & high impedance length, but what's the inductance made by the coil?
For that we would need to know the electrical length of the shield beneath the medium of the casing which offers some unknown velocity factor.
I sure wish Sirio would post the secrets of the Gainmaster on this forum!
NB, good to see you back.
I don't understand the math here, but the frequency result you get is exactly what Sirio claims as their bandwidth center frequency, so maybe your idea and calculations are correct.
BTW, how are you coming on your Sigma4/Vector project that proves, once and for all, whether the bottom 1/4 wave cone radiates or not? When that happens will you have something to show us, or will the report just be words?
I'll be making a VIDEO.
- WHEN I can afford to buy a decent computer or figure out why this POS won't allow me to do 1/2 the stuff I should be able to do. :headbang
Where you been Needle?
I tell you these computers are alot of work. Sometimes i forget to run adaware/malware and before you know it, the darn things got my computer crawling as slow as a turtle.
any way don't want to jack the thread, but yesterday I googled and found one feller in South america (i believe) that had made his own homemade GM, but he only posted pics of it and no other information...
I tell you these computers are alot of work. Sometimes i forget to run adaware/malware and before you know it, the darn things got my computer crawling as slow as a turtle.
any way don't want to jack the thread, but yesterday I googled and found one feller in South america (i believe) that had made his own homemade GM, but he only posted pics of it and no other information...
Re: "Where you been Needle?"
...getting BENT - over by this computer. It lost a win32 file and had to go to the Doc for resurrection, but it still locks up if I try the simplest of things and I've run Viper, and 2 other paid virus scanners but to no avail. Thinking maybe it's the HD getting ready for retirement, though it's not that old. My LAST Dell, that's fer shurr.
I've never had a computer as pleasing as the old E-monster (AMD Athalon processor) since it went the way of all over-used HDs. If I get a new one it will not be Pentium based if I can help it.
Got a local radio guy interested in helping to get the video made & uploaded so it might be 'sooner than later', Marconi.
needle I'd start by uninstalling all but one anti-virus.
most don't play well together - I get trying to vigilant with security but you'll create a lot of headaches running systems that may see each other as "intruders".
Once you've got yourself pared down to a single AV find CCleaner on the net and use it "carefully" to get things on the system sorted out. It's a very good and very powerful application... if you're not careful though you can also Zorch your system so be sure to set restore points as you go.
HB GM
Hi, sorry for the delay in replying hit an oil patch on the way to work the other day on my motor bike and the road won! have got a realy sore left arm and wrist.
Back to this strange antenna, all the details and plans I have from the guy in Portugal who has built and uses a home brew GM seemingly working very good even posted on youtube and had a piece in the radio user mag? I will see if I can post them up here but if not will have to link to something like photobucket as the plans are the original GM plans with his details written on them, the maths were from a directed link on the net giving the formulas for getting coax capacitance lengths (he recomends two kinds) and another link for different coax quarter wave stub matches (loads of letters and brackets which you replaced with velocity factors and desired frequency to hard for me) I have those on a scrap of paper somewhere, the 9cm one is the one the Potugese geezer used and he reports it works fine I used a different coax that was lying about.
Any clues how to post giff or jpeg up here?
Phil
Hi, sorry for the delay in replying hit an oil patch on the way to work the other day on my motor bike and the road won! have got a realy sore left arm and wrist.
Back to this strange antenna, all the details and plans I have from the guy in Portugal who has built and uses a home brew GM seemingly working very good even posted on youtube and had a piece in the radio user mag? I will see if I can post them up here but if not will have to link to something like photobucket as the plans are the original GM plans with his details written on them, the maths were from a directed link on the net giving the formulas for getting coax capacitance lengths (he recomends two kinds) and another link for different coax quarter wave stub matches (loads of letters and brackets which you replaced with velocity factors and desired frequency to hard for me) I have those on a scrap of paper somewhere, the 9cm one is the one the Potugese geezer used and he reports it works fine I used a different coax that was lying about.
Any clues how to post giff or jpeg up here?
Phil