WHAT IS A DOUBLET ? - G5RV - ZS6BKW

[@DXCommanderHQ]

My take Stu - and this comment for future readers, not you - and I'm only half way through video as I type! Balanced feeder has extremely low loss even while suffering extremely high SWR (unlike coax which does have high losses on extreme SWR). Assuming you have a good outboard tuner, you can be very efficient with a doublet by making the tuner effectively part of the antenna circuit and delivering a good amount of wigglies to the doublet elements and massive SWR. Band changes are a pain in the ass though.. Now then.. G5RV (and derivatives) use a very particular length of balanced feeder as an impedance transformer (transmission line theory which I'm crap at) to give you a FAIRLY good match at a specific point in time (frequency) where you can connect your coax and in the main, achieve better than 2:1 SWR. Then in the late 60s, Brian (G0GSF / ZS6BKW) worked out (with a slide rule - really!) that by adjusting G5RVs dimensions, he could achieve very slightly better match on 20m. Now for the killer... He also said that on 20m, due to some imbalances, that the vertical part of the ladder line also radiates. I just don't understand that bit...! So to conclude! A G5RV is a Doublet with some trickery on the balanced line length, a doublet in the main doesn't care about any lengths - just a fat high quality outboard tuner (say Palstar At4K) and a Dipole needs precise element lengths to give you a pretty close match to 50 ohms for your coax. We don't use a tuner to tune the nuts off a coax dipole. ALso doublets can give you some weird patterns if you use big ones on higher bands.. Geez. I don't often type that much!!

[@G5STU]

Cheers Cal, I've used a doublet but the constant retuning is a ball ache, from what I've heard the G5RV type antennas are very fussy when it comes to installation as they are obviously length / height specific (i.e need to be correctly tuned). I only use antennas I can plug straight into the Acom these days. Happy new year.

[@andy2E0JIU]

Cal I remember the doublet you had up a few years ago now,worked awesome n you were always strong especially on 80m

[@timg5tm941]

I’d just whack up a dipole and feed it with 300/450 ohm window line. Run the feeder either to a balanced tuner or via a beefy 1:1 current Balun and a short piece of thick coax to an unbalanced tuner. The G5RV and ZS6BKW are convenient but bloody fussy antennas in many ways as their USP depends on specific dipole and feeder lengths. More a triumph of mathematics over real world simplicity IMHO.

[@G5STU]

yep, I can see why people lean towards the end fed half wave for multi band as they are just more tolerant to a `bad` insulation although I'm not a fan as they just don't work well on the higher bands in my experience, which is why I have the vertical.

[@g4lmn-ron401]

I was fortunate to go to a couple of lectures given by Lou, G5RV, where he talked about his antenna. Lou was surprised at the popularity of the antenna.The G5RV is from the valve era of output stages and it was fed with ladder line, wide spaced stuff, 150mm, then 72 ohm twin feeder, no coax in sight. The tune was done with the output stage of the radio. I don't think it works well in the modern era because we have way more bands now than in 1947 and rigs with solid state output stages. The ZS6BKW works better, and I have one of these but it still needs a tuner and is a pain in the bum. The end fed half wave and/or Callum's fan vertical are the way to go in the 21st Century IMO. Happy New Year!

[@John_Ai9D]

Great explanation! Thanks!

[@stevegordon2869]

I have used g5rv and tried zs6bkw. I cut the coax off g5rv ladder line all the way to mfg-962 tuner works wonderfully no rf in shack with 500watts. I have have used fan dipole before. I get bored with that quickly. I love the idea of antenna tuners so 450 ohm line is my thing.also found 102 ft top with 90 to 100 ft feed line is easy to tune. 115 ft is hard to tune low band width on 20meter. 73s

[@2SD251Jim]

Nonsense....your not drinking tonight???😂😂😂😂

[@G5STU]

🤣 happy new year Jim

[@2SD251Jim]

HAPPY NEW YEAR MY FRIEND...NX8T

[@G5STU]

What did I get wrong ?

[@Bobby63208]

Dublet was a very dangerous horse down here in the late 1980's 😆

[@artc9114]

G5RV or ZS6BKW antennas are not Doublet antenna systems. A true Doublet from any old ARRL antenna handbook is achieved by using a 300ohm, 450ohm ladder line or preferably 600ohm balance line directly terminated to the back of an L or T network type balanced tuner/matchbox, then cutting the antenna legs length to the lowest band of operation. No COAX at all for minimum losses which gives maximum efficiency. A G5RV or ZS6BKW must have at least 50-plus feet of coax to counterbalance the antenna, tuner, and radio.

[@G5STU]

That's what I said.

[@brianhind6149]

Sorry...all feedlines have loss. Open wire balanced feedlines have low losses compared to co-ax lines.

[@G5STU]

That’s what I said

[@artc9114]

but the advantage of a true doublet fed with open balance lines is the ability to tune the antenna system from 10 to 160-meter bands with way less loss than coax which makes it a great multiband antenna system for the path of least resistance.

[@m0ttf]

Happy new year de mw0ttf