Home |
Search |
Today's Posts |
#1
|
|||
|
|||
Sources for Inexpensive RG-8??
I'll have some fairly long runs of coax to HF antennas (21Mhz max) to
Field Day antennas. One of the antennas will be an 80M G5RV with their usual nasty SWRs so a foam-type cable is indicated. Since it's a very temporary non-critical installation I'm not about to spend premium bucks on 9913 or any of it's relatives like I do for the home station. A non-contaminating jacket would be nice but is not much of an issue. Does anybody have any suggestions about vendors who are selling foam RG-8 for lower-than-usual prices? Thanks, Brian w3rv |
#2
|
|||
|
|||
On 2 Apr 2004 07:38:00 -0800, Brian Kelly wrote:
I'll have some fairly long runs of coax to HF antennas (21Mhz max) to Field Day antennas. One of the antennas will be an 80M G5RV with their usual nasty SWRs so a foam-type cable is indicated. Since it's a very temporary non-critical installation I'm not about to spend premium bucks on 9913 or any of it's relatives like I do for the home station. A non-contaminating jacket would be nice but is not much of an issue. Does anybody have any suggestions about vendors who are selling foam RG-8 for lower-than-usual prices? Thanks, Brian w3rv Could you get hold of 75 ohm cable instead? G5RV recommended it for this antenna anyway and regardless of what you use you will need a tuner. RG 59 may be cheaper and CATV cable may be free or someone may have enough to help you out. 73 de VE3JUA. |
#3
|
|||
|
|||
Brian Kelly wrote:
I'll have some fairly long runs of coax to HF antennas (21Mhz max) to Field Day antennas. One of the antennas will be an 80M G5RV with their usual nasty SWRs so a foam-type cable is indicated. Hi Brian, what bands will the G5RV be used on? Only 80m? The SWR is not all that nasty on 80m being about 20:1 on the ladder-line and 2:1 on the coax. Here's one of my rules-of-thumb for which I am infamous. :-) Given a 102 ft. Dipole at 40 ft. fed with 450 ohm ladder-line and used on 3.8 MHz, for a ladder-line length between about 25 ft. and 100 ft., the resistance looking into the ladder-line is about equal to the length of the ladder-line. Thus for 25 ft. of ladder-line, the impedance looking into the ladder-line is about 25+jXL1. For a ladder-line length of 50 ft., the impedance looking into the ladder-line is about 50+jXL2. For a ladder-line length of 100 ft., the impedance looking into the ladder-line is about 100+jXL3. Does that give you any hints on how to match it? According to EZNEC, the impedance looking into 50 ft. of ladder-line is about 50+j466. Use two series 180pf caps to neutralize the inductive reactance and you have a feedpoint impedance of 50 ohms. A dual ganged 300pf variable would be ideal. A 102 ft dipole 40 feet in the air fed with 50 ft of ladder-line tuned with a dual-gang variable cap on the antenna side of a balun/ choke and no tuner box. Doesn't that sound like a perfect 75m field day antenna? -- 73, Cecil, W5DXP |
#4
|
|||
|
|||
Cecil Moore wrote:
Given a 102 ft. Dipole at 40 ft. fed with 450 ohm ladder-line and used on 3.8 MHz, for a ladder-line length between about 25 ft. and 100 ft., the resistance looking into the ladder-line ^^^^^^^ is about equal to the length of the ladder-line. Thus for 25 ft. of ladder-line, the impedance looking into the ladder-line is about 25+jXL1. For a ladder-line length of 50 ft., the impedance looking into the ladder-line is about 50+jXL2. I misspoke above. "100 ft." should have been "50 ft." For a ladder-line length of 100 ft., the impedance looking into the ladder-line is about 100+jXL3. It is true that the resistance for 100 ft. of ladder-line is about 100 ohms, but it is 100-jXC, not 100+jXL. Sorry for the faulty memory. -- 73, Cecil, W5DXP |
#5
|
|||
|
|||
Cecil Moore wrote in message
A 102 ft dipole 40 feet in the air fed with 50 ft of ladder-line tuned with a dual-gang variable cap on the antenna side of a balun/ choke and no tuner box. Doesn't that sound like a perfect 75m field day antenna? I hope you are successful in making people think so. :/ It'll be easier pickings for me and my superior, lower overall loss, radiating device. I already use the *perfect* 75m field day antenna. It's a regular old full size coax fed dipole. Why would anyone want to clutter up low loss perfection? Boggles my mind...:/ But it's ok, like I said, it's to my advantage on that bug infested night in June. I hope everyone else is using G5RV's, windoms, isotrons, EH's and other such things.. Makes it easier for us. . MK |
#6
|
|||
|
|||
Mark Keith wrote:
Cecil Moore wrote in message A 102 ft dipole 40 feet in the air fed with 50 ft of ladder-line tuned with a dual-gang variable cap on the antenna side of a balun/ choke and no tuner box. Doesn't that sound like a perfect 75m field day antenna? I hope you are successful in making people think so. :/ It'll be easier pickings for me and my superior, lower overall loss, radiating device. I already use the *perfect* 75m field day antenna. It's a regular old full size coax fed dipole. Why would anyone want to clutter up low loss perfection? Boggles my mind...:/ But it's ok, like I said, it's to my advantage on that bug infested night in June. I hope everyone else is using G5RV's, windoms, isotrons, EH's and other such things.. Makes it easier for us. . MK I suspect the above antenna is more efficient than your coax-fed dipole. There's negligible loss in the 50 ft. of ladder-line and negligible loss in the series caps. No tuner required, therefore no lossy coil. So where's the loss? Please be specific and provide data to back it up. -- 73, Cecil, W5DXP -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
#7
|
|||
|
|||
Cecil Moore wrote in message
I suspect the above antenna is more efficient than your coax-fed dipole. There's negligible loss in the 50 ft. of ladder-line and negligible loss in the series caps. No tuner required, therefore no lossy coil. So where's the loss? Please be specific and provide data to back it up. I suspect you would be in for a surprise at field day.. What about your balun/choke connection? I assume you will be running coax to that choke, and then to 50 ft of ladder line? And the variable cap on the antenna side of the choke...How convenient... All I can say is why? There is no way on earth that setup is *more* efficient than a coax fed dipole. It may be *fairly* efficient, maybe even quite so if you are real lucky, but it's not going to be as good as the full size dipole fed with good coax. No way. The only real loss I have is the loss of the feedline "213", and on 80m, it's about as good as ladder line. Dunno...I think complicated gimmicky setups that are inferior to the ultra simple coax fed dipole are kind of silly. :/ But to each his own. If it were better, I could see it. But it's not. It's inferior. If it were not, I would be using one here at the house. Why would anyone want to do more work, for something a step in the wrong direction? Boggles me mind...I've never seen why people want to use smaller or compromise antennas when you have the whole wide outdoors to string up anything you want. The "average" storebought G5RV is pitiful on 80m compared to the coax fed dipole. Not even a real contest. But everyone ignore what I say. I'm really fibbing, and just messing with ole Cecils head....I suggest all field day op's on 80m use G5RV's, windoms, isotrons and EH antennas. If you all follow my advice, I might be able to mop up quick, and be able to go home early and get some sleep in my cool, bug free, air conditioned bed.. :/ MK |
#8
|
|||
|
|||
Mark Keith wrote:
What about your balun/choke connection? W2DU choke, virtually lossless. The tuning cap is also virtually lossless, much more so than a tuner with a coil. The only real loss I have is the loss of the feedline "213", and on 80m, it's about as good as ladder line. It's about as good as open-wire line with a 10:1 SWR. The matched line losses in 100 ft. of RG-213 are higher than the unmatched line losses in 100 ft. of open-wire line with a 10:1 SWR on 80m. According to Wirebook II, the matched line loss for RG-213 is ten times higher on 80m than the matched line loss for open-wire line. If it were better, I could see it. But it's not. It's inferior. If it were not, I would be using one here at the house. You are so biased, you wouldn't use one if your life depended on it. :-) Why would anyone want to do more work, for something a step in the wrong direction? It's a step in the right direction, Mark, toward an all-HF-band antenna. I modified my G5RV yesterday to work well on all eight HF bands plus 6m. Field strength measurements indicated it is virtually identical to my 130 foot dipole on 80m. The "average" storebought G5RV is pitiful on 80m compared to the coax fed dipole. Mine is virtually equal to a resonant dipole. Your "average" storebought G5RV must be poorly designed - maybe lacking a balun - maybe using RG-58 coax - maybe using the wrong length of the series section transformer. But everyone ignore what I say. I'm really fibbing, and just messing with ole Cecils head... I asked for some scientific proof of what you say. All you responded with is prejudice and hand-waving. Please take time to calculate the matched line losses in RG-213 Vs the unmatched line losses for open-wire line and you will change your mind (if you are rational). -- 73, Cecil, W5DXP -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
#9
|
|||
|
|||
Cecil Moore wrote in message ...
Brian Kelly wrote: I'll have some fairly long runs of coax to HF antennas (21Mhz max) to Field Day antennas. One of the antennas will be an 80M G5RV with their usual nasty SWRs so a foam-type cable is indicated. Hi Brian, what bands will the G5RV be used on? Only 80m? The SWR is not all that nasty on 80m being about 20:1 on the ladder-line and 2:1 on the coax. Greetings Cecil: I've been on the road for the past three days and am just now catching up with my e-mail and such. The answer to your question is that I intend to use a Van Gordon 80M G5RV at about 40 ft. on 80/75/40 as a minimum. I'm "ambidextrous", I motor-mouth and twitch paddles on FD so I need "bandwidth" on 80/75. I'm building a close-spaced wires duo-band dipole for 20 & 15 which will be hung at around 25-30 ft. If that antenna doesn't work right I'll also have to use the G5RV on 20/15 too. In the ideal scenario both antennas would work and I'll be able to swap antennas around for 20 & 15 depending on the pattern & propagation condx of the moment. I'll use 8X to feed the G5RV balun which will be 8-10 foot above ground level to keep the weight on the G5RV down From there I'll run a length of RG-8 to the operating position. Looks like a 75 or so foot run. I'll use my LDG-11MP ATU to tame the G5RV. With all this coax involved the ATU won't have much "work" to do . . . Here's one of my rules-of-thumb for which I am infamous. :-) Heh. Given a 102 ft. Dipole at 40 ft. fed with 450 ohm ladder-line and used on 3.8 MHz, for a ladder-line length between about 25 ft. and 100 ft., the resistance looking into the ladder-line is about equal to the length of the ladder-line. Thus for 25 ft. of ladder-line, the impedance looking into the ladder-line is about 25+jXL1. For a ladder-line length of 50 ft., the impedance looking into the ladder-line is about 50+jXL2. For a ladder-line length of 100 ft., the impedance looking into the ladder-line is about 100+jXL3. Does that give you any hints on how to match it? According to EZNEC, the impedance looking into 50 ft. of ladder-line is about 50+j466. Use two series 180pf caps to neutralize the inductive reactance and you have a feedpoint impedance of 50 ohms. A dual ganged 300pf variable would be ideal. A 102 ft dipole 40 feet in the air fed with 50 ft of ladder-line tuned with a dual-gang variable cap on the antenna side of a balun/ choke and no tuner box. Doesn't that sound like a perfect 75m field day antenna? I've read the whole thread thru Tuesday AM, I get your point and it should work well on 80. I suspect the real advantage of your scheme is that it might be possible to cover both 80 and 75 with low overall losses which is difficult to accomplish with a fullsize dipole. Since you already have the EZNec model on hand how 'bout running a 3.50-3.85 Mhz. sweep to see if it's possible to cover that range with some single specific length of ladderline and the two-section BC variable cap? If yes I think you have a real keeper idea. Davis RF has "RG-213 Economy" cable, whatever that is, for $0.23/foot. Good enough for Field Day. Brian w3rv |
#10
|
|||
|
|||
Eskay wrote in message ...
On 2 Apr 2004 07:38:00 -0800, Brian Kelly wrote: I'll have some fairly long runs of coax to HF antennas (21Mhz max) to Field Day antennas. One of the antennas will be an 80M G5RV with their usual nasty SWRs so a foam-type cable is indicated. Since it's a very temporary non-critical installation I'm not about to spend premium bucks on 9913 or any of it's relatives like I do for the home station. A non-contaminating jacket would be nice but is not much of an issue. Does anybody have any suggestions about vendors who are selling foam RG-8 for lower-than-usual prices? Thanks, Brian w3rv Could you get hold of 75 ohm cable instead? G5RV recommended it for this antenna anyway and regardless of what you use you will need a tuner. RG 59 may be cheaper and CATV cable may be free or someone may have enough to help you out. Using 75 ohm coax is probably a good idea, I'll look into it. But I don't want to use any small-diameter coax, the losses would be prohibitive considering the lengths of runs I'll use. 73 de VE3JUA. Brian w3rv |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|