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1.5 KW PEP Gain-Master Modification

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  #25  
Old 05-11-2011, 05:28 AM
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Originally Posted by NRG View Post
i found others that are not the same spec but they claim to use teflon
http://www.crownelectronics.com/Specs/RG-393
RG-393/U Coaxial Cable; 50ohm [RG393U] : Cross RF, RF & Microwave Interconnect Essentilals
Buy M17/127-RG393 Online from Allied Wire & Cable | Distributor of Coaxial Cables
i also found some rg303 that was 70%vf and 32pft
did you get the specs directly from sirio? i dont mean to act doubtfull but i just dont wanbt to have to mod it more than one time. just too much work for my bad back.
Imagine that, cables that carry the same part number and Mil Spec number are not necessarily the same after all! The original RG-303 coax is manufactured by Habia Cable in the UK. It has a velocity factor of 70% and the capacitance is 94 pf per meter or 28.65 pf per foot. The velocity factor is more important when dealing with matching stubs and phasing cables then it is in this case. Since the cable is being used as a capacitor its pf rating is most important.

The 0.75 pf difference in the Times Microwave coax made no change in the bandwidth that I could see once the top black wire was trimmed to compensate for the extra length the braid adds. Apparently the differences in specifications between these two manufacturers of RG-393 are well within the tolerance required to match this antenna. It's still a good idea to match the specs to the original as close as possible and I thank NRG for pointing this out because I was unaware of it.

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  #26  
Old 05-11-2011, 06:39 AM
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Originally Posted by Shockwave View Post
Imagine that, cables that carry the same part number and Mil Spec number are not necessarily the same after all! The original RG-303 coax is manufactured by Habia Cable in the UK. It has a velocity factor of 70% and the capacitance is 94 pf per meter or 28.65 pf per foot. The velocity factor is more important when dealing with matching stubs and phasing cables then it is in this case. Since the cable is being used as a capacitor its pf rating is most important.

The 0.75 pf difference in the Times Microwave coax made no change in the bandwidth that I could see once the top black wire was trimmed to compensate for the extra length the braid adds. Apparently the differences in specifications between these two manufacturers of RG-393 are well within the tolerance required to match this antenna. It's still a good idea to match the specs to the original as close as possible and I thank NRG for pointing this out because I was unaware of it.

.75 pf?

You can walk into the room and change capacitance more than that.

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Old 05-11-2011, 07:42 AM
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ok ill use times and thanks for clarifing that. i cant spell fer sh!^ but i try to do my homework i was just thinking about the strength of it and how the whole wait is on the sheild of the times. do you think it would be smart to use parashoot cord from the top down to below the conector in the middle with epoxy as a wait baring asisst? i just spent a year on the habai.com website and cant find any specs for 303.

Last edited by NRG; 05-11-2011 at 08:24 AM.

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  #28  
Old 05-11-2011, 08:31 AM
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Originally Posted by NRG View Post
ok ill use times and thanks for clarifing that. i cant spell fer sh!^ but i try to do my homework i was just thinking about the strength of it and how the whole wait is on the sheild of the times. do you think it would be smart to use parashoot cord from the top down to below the conector in the middle with epoxy as a wait baring asisst? i just spent a year on the habai.com website and cant find any specs for 303.
The braid of the RG-393 is a double braid that is silver plated copper. The end where the black wire is soldered to has been tinned all the way around the coax so that it's bonded to all of the strands in the braid. It looks like it is much stronger then the black wire itself. Sealing it in the double wall heat shrink tubing lined with hot glue inside, locks the entire unit together very well. The weight of the cable is nearly nothing. Adding the parachute cord inside the fiberglass from the top down could change the Velocity factor and VSWR a little. Here is the PDF page for the Teflon cables from Habia: http://www.aerco.co.uk/images/sub_su...able-types.pdf

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  #29  
Old 05-11-2011, 08:47 AM
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thanks again. so you ended up cutting of about 3-4" of the black wire right? i have had bad luck with hot glue melting in the heat and summer gets real hot in phoenix. what about 20 minute epoxy instead?

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Old 05-11-2011, 08:56 AM
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Originally Posted by NRG View Post
thanks again. so you ended up cutting of about 3-4" of the black wire right? i have had bad luck with hot glue melting in the heat and summer gets real hot in phoenix. what about 20 minute epoxy instead?
That's correct. The amount you cut off is equal to the length of the braid on the new capacitor. This does not include the extra length of braid soldered to the bottom of the board or the small length of black wire that is overlapped on the braid for soldering. I recommend using a VSWR meter to trim this wire back to the original bandwidth. This can be done with a 10 foot pole on the ground in the open.

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Old 05-11-2011, 09:05 AM
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ok now comes the time to spend money. i hope it beats my a99 at least $200 worth what about using epoxy? do you think thast is as invisible to rf as the hot glue?

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  #32  
Old 05-11-2011, 12:18 PM
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I sent the link to this page to one of the engineers @ Sirio, a "Lorenzo Mezzadrelli". He just sent me a note back and said that he thought it was interesting. He might become a member and input here. WE will see . . .
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