HOW TO GET RF OUT OF THE SHACK

[w3duq]

I have been trying a G5RV on 75 and there is rf everywhere- especially in the shack.  HOWEVER, using the old tv twin lead / aluminimum foil ploy I cleaned it up.
Here is what you do:

make a multi loop arrangement with about 3 fot loops from a piece of coax about 50 feet long and insert it in series with the g5rv coax in the shack.  NOW, take a couple of 12 inch pieces of aluminum foil and wrap it around the coil of coax.  Voila- no more rf in the shack !!

[KB2WIG]

paper towel  cardboard rolls filled with steel wool works 4 me

[Steve - WB3HUZ]

I use a piece of coax to get the RF out of my shack. Takes it right up to the antenna where it radiates. The best length to use is the one that spans the distance from your transmitter to your antenna. FB OM>

[Pete, WA2CWA]

From one of the g5rv trivia sites:
"Under certain conditions, either due to the inherent "unbalanced-to-balanced" effect caused by the direct connection of a coaxial feeder to the base of the (balanced) matching section, or to pick-up of energy radiated by the antenna, a current may flow on the outside of the coaxial outer conductor. This effect may be considerably reduced, or eliminated, by winding the coaxial cable feeder into a coil of 8 to 10 turns about 6in in diameter immediately below the point of connection of the coaxial cable to the base of the matching section. the turns may be taped together or secured by nylon cord."

[W5AMI]

I need to do this on my HF beam, but I'm wondering what coax to use so that the center conductor does not migrate too far and get too close to the shield.  I've heard some is better than others, but not sure which.  I've got 9913 high flex.  Will that be okay to roll in a 6" diameter coil, or should I use something like 213 for the choke?

[WA1GFZ]

RF is the reverse of sewage it wants a good pipe heading upward to the sky.
I would use RG213 or RG214 but 1/2 inch andrews would also be good.
Tom Vu did a thing on coax baluns a while back check back in time for the data.
I used this very cool big teflon coax on my log for my balun. I've never seen it listed anywhere but much bigger than RG393. I think it was 8 turns 8 inch ID.

[WA1GFZ]

I thought 213 was the same as 8 but a better shield coverage. Yup stay away from foam on a tight radius bend. 214 is double shielded silver plated shield solid dielectric.

[Steve - WB3HUZ]

I'm thinking just don't use a G5RV and the problem is solved.

[WA1GFZ]

Yea wasn't the G5RV designed by Lucas Electric?
Get an amerikan antenna

[K1JJ]

I'm thinking just don't use a G5RV and the problem is solved.

Yep, I agree.  Use the G5RV for parts, Bill. You have plenty of room to put up a separate antenna for 160, 75 and 40M.

The right way is to wind 10-12 turns of coax on a 4" ABS or PVC plastic form and mount it right at the dipole's feedpoint. One antenna for each band.   The idea of going from a balanced G5RV openwire feedline to unbalanced coax using a simple coaxial choke scares me to the point of volunteering to be the first citizen to receive a govt brain mind-control implant.  (It will "work", but why not do the job right?)


T

[Steve - WB3HUZ]

The G5RV was originally designed for use on 20 meters. Trying to make it a multiband antenna seems futile.

Heh, heh.. Lucas Electric. Their switches have two positions: Off and Intermittent.

[Pete, WA2CWA]

I need to do this on my HF beam, but I'm wondering what coax to use so that the center conductor does not migrate too far and get too close to the shield.  I've heard some is better than others, but not sure which.  I've got 9913 high flex.  Will that be okay to roll in a 6" diameter coil, or should I use something like 213 for the choke?

I just replaced my old Hy-Gain balun on the Wilson System 1 Tribander with one from DX Engineering. Old one was up there for 25 years. Case was cracked from weathering. I use 9913F7 coax from the balun, around the rotor, and down to the shack. For years I used RG214. Great cable for straight runs, but with the double shield, it's not very fexible.

[Pete, WA2CWA]

I'm thinking just don't use a G5RV and the problem is solved.

Yep, I agree.  Use the G5RV for parts, Bill. You have plenty of room to put up a separate antenna for 160, 75 and 40M.

The right way is to wind 10-12 turns of coax on a 4" ABS or PVC plastic form and mount it right at the dipole's feedpoint. One antenna for each band.   The idea of going from a balanced G5RV openwire feedline to unbalanced coax using a simple coaxial choke scares me to the point of volunteering to be the first citizen to receive a govt brain mind-control implant.  (It will "work", but why not do the job right?)

T

Have to agree with Tom here. Going from balanced line to an unbalanced coax connection, with or without a simple coaxial choke, is still probably not the best design criteria. I would also vision a nice transmission line bump right at that junction. If you want multi-band action with one antenna, why not just run the balanced line directly into a balanced line tuner. Mount the tuner either remotely or directly in the shack.

[K1JJ]

I thought 213 was the same as 8 but a better shield coverage. Yup stay away from foam on a tight radius bend. 214 is double shielded silver plated shield solid dielectric.

What ya need is RG/213/U Mil-C17 or equivalent. This uses a hard polyethylene dieletric. I just went through 1000' and ordered 1000' more. It can be had cheaply at the surplus outfits.

HOWEVER, there are many outfits selling a so called RG-213 that is cheap, possibly foam and not mil spec. I saw an ad on the web offering it real cheap/ft and axed them about the mil spec. Turns out it was a CB company. Here's the professional response I got : "Sir we dont carry that coax te coax we have we get is from Workman thanks"....   caw mawn.

Here's the real spec: 50 Ohm 95 % Shield 66 % Velocity 30.80 pF/ft. Capacitance .285" Solid Polyethylene Insulation .405" Black Non Contaminating PVC Jacket

I once axed the vendor of the Mil-spec RG-213 if his RG-213 was mil spec. He laughed and said that ALL RG-213 was supposed to be mil spec.  But as I have found, there are knock-outs that are not.


And the plot thickens - I just found this on the web:

"By the way, there is no such thing as RG-213/U any more.  It's been discontinued as a spec (DoD doesn't buy polyethylene insulated wire any more due to fire hazard), so all you really can get is: "manufactured to meet (cancelled) MIL STD-c-17-74 RG/213" or "RG-213 type"

So, guess you just have to see a sample these days or buy and old roll with the mil spec printed on it.


T
 

[John Holotko]

The G5RV was originally designed for use on 20 meters. Trying to make it a multiband antenna seems futile.

Heh, heh.. Lucas Electric. Their switches have two positions: Off and Intermittent.

I've never used or experimented with a G5RV myself  but most of the times  I've heard them used on the 40 or  75meter bands the signals  have been relativelyweak, i.e.I haven't heard anyone really strap on 75 with a G5RV. Personally I like an open wire fed dipole or inverted vee coupled via a REAL link coupled tuner.

[K1JJ]

I've never used or experimented with a G5RV myself  but most of the times  I've heard them used on the 40 or  75meter bands the signals  have been relativelyweak, i.e.I haven't heard anyone really strap on 75 with a G5RV.

I've often wondered this myself... why are the G5RV guys usually weaker than they should be?

I think the reason is that many newcomers buy them as a first antenna. They think it will handle everything. Just like me and my first experience with a Gotham vertical. Most newcomers put up antennas that are low to the ground, zig zagged around the yard - balanced line too close to objects creating inbalances, etc. Thus, G5RV's don't usually get the break they need to perform.

The reason I say this is that a G5RV modeled should be within a db or so to a full sized dipole if put up straight, at the same height, in the clear. The 2:1 or 3:1 swr on various bands is really insigificant. My challenge someday will be to actually put one up in the clear at 60' and see if anyone can tell the difference between it and a full sized coax fed dipole. I think not. 

The major disadvantage of the G5RV is on the higher bands where the pattern turns into a multi-lobed octopus. This can't be helped even with an open wire fed dipole cut for 75 or 160M used up on 20-10M. 4X the freq gives a cloverleaf with a big null in the front lobe. (A 160M dipole used on 40M = four lobes with a null broadside ... on 20M = eight lobes, etc)

I still recommend a separate coax fed dipole for each band to give a predictable, broad figure 8 pattern. (With 1:1 coax choke balun at the feedpoint)  As second choice, an open wire fed dipole and tuner. The G5RV would be a last resort, but still a good performer if erected high and straight.

T

[Glenn NY4NC]

What was that routine about.. "I have a G5RV and a Kenwood 520, can I be a strapping Am'er on 75?"

 

(something like that...)

[Pete, WA2CWA]

What was that routine about.. "I have a G5RV and a Kenwood 520, can I be a strapping Am'er on 75?"

 

(something like that...)

I don't think the 520 does AM but I agree with the point.

G5RV's seem to be the 21st century Gotham antennas.

[W3SLK]

Steve said:

The G5RV was originally designed for use on 20 meters. Trying to make it a multiband antenna seems futile.

I think I would dispute that, Steve. Duane, KK4AM (sans KN0R), had one that we doubled the size of the flat top and the 450 ohm feeder, (from 102' to 204'; 32'feeder to 64' feeder). It worked quite well on 160, 75, & 40 that I know of. But I will agree with you on attempting to use the original G5RV on 160 was feeble at most. Running in Marconi style let you work all TV's, radios, stereos, etc.

[Pete, WA2CWA]

I don't think the 520 does AM but I agree with the point.

Glenn may be thinking of the TS-830M which did give you 40W AM.

Mark K3MSB

Could be, but not many around here in the U.S. since they were never sold here new. Low level modulator with, I think, only rated at 25 watts.

[Blaine N1GTU]

i turned off my transmitter, now the RF is completely gone 

[k4kyv]

. 214 is double shielded silver plated shield solid dielectric.

I once used some military surplus 214 outside, exposed to the sun.  The UV did a job on the outer jacket.  It just sort of became a mosaic, with cracks in a rectangular pattern.  Water got in, contaminated the dielectric, and efficiency dropped from over 90% to about 70%.  Also, critters started gnawing holes in the part of the jacket that was buried.

I think I  still have it around here somewhere. Might be useful for constructing a small ground radial system.

Picked up some direct-burial RG-213 at a hamfest, and have never had any problem with it.  Mine is solid dielectric, not foam.

[K1JJ]

Hey Ozzie - woof woof!    Blaine - I found some of Ozzie's fur here and let Yaz smell it. He recognized it and went looking around for him....    He wants to see Ozzie again!

[k4kyv]

"By the way, there is no such thing as RG-213/U any more.  It's been discontinued as a spec (DoD doesn't buy polyethylene insulated wire any more due to fire hazard), so all you really can get is: "manufactured to meet (cancelled) MIL STD-c-17-74 RG/213" or "RG-213 type"

Now I guess they really are worried that coax dielectric is going to burst into flames!

[K1JJ]

I once used some military surplus 214 outside, exposed to the sun.  The UV did a job on the outer jacket.  It just sort of became a mosaic, with cracks in a rectangular pattern.  Water got in, contaminated the dielectric, and efficiency dropped from over 90% to about 70%.  Also, critters started gnawing holes in the part of the jacket that was buried.

Don, I noticed the same kind of cracks EVEN on the RG-213/U mil-C17 stuff.  I have some baluns that were in the sun for a few years and show the cracks, though the inside is still bright and shiny. I'm wondering if spray painting the outside with enamel paint will solve the problem, or at least keep it good for a few more years.. The baluns are small enuff. I just took them down for maintainence and can get at them. The main feedlines are new, so no worry there.

T