PA0RDT mini-whip  - Page 1
Forum section: electronics / rf-microwave

author: Terry Bites
author_rank: Super Contributor
timestamp: June 26, 2024, 07:09:24 am
content: I'm not an RF bod.I'm interested in using a PA0RDT mini-whip. I know it has to be mounted above ground on a non-conductive pole but will a few stainless steel ties near the socket end affect its performance?What might be a robust and rational way to afix it to a 30mm carbon fibre pole.I’m averse to nylon cable ties on the grounds that I can’t predict how long they’ll last. Any ideas, experiences?I am also toying with idea of diplexing my passive VHF on the same down cable. Advice, ideas?Cheers

author: A.Z.
author_rank: Super Contributor
timestamp: June 26, 2024, 08:56:15 am
content: Quote from: Terry Bites on June 26, 2024, 07:09:24 amwhere did you hear about the "non conductive pole" ?In my experience, the correct way to install a "miniwhip" is shown in the two images belowin short, the antenna is installed on a metallic pole (connected at bottom to a ground stake with a very short run of fat wire or, if a stake isn't viable, to a metal grid laid on ground) as up and in the clear as possible, but using a clamp (or a piece of PVC pipe tied to the pole) so that it stands ABOVE the pole and the ground (shield) of the coax has a good electric connection to the pole (see first image), the coax then runs downward along the pole (tie it to the pole using good UV resistant "nylon" cable ties in pairs) and, at bottom we'll place at least one good choke (three spaced ones would be better), for example 15 turn of coax wound on an #43 material toroidIf possible, that is if a roof terrace or a garden is available, the antenna should be placed as far away as possible to keep it at a distance from the cloud of domestic "electrosmog", also, the bias-tee power supply should have good filtering so that it won't inject noise in the antenna preamp, so avoid using "phone chargers" or generic "brick" PSUs and pick a decent oneregarding the coax, a general rule is to stay away from RG-58/RG-174 and use a better (lower loss, better shielding) type of cable, for example RG-213you can find further infos regarding the "miniwhip" and other active antennas herehttps://web.archive.org/web/20230722120107/https://www.g8jnj.net/activeantennas.htmsorry for the link to "web archive" but Martin's site was migrated tohttps://g8jnj.net/and is currently "under rebuild"

author: A.Z.
author_rank: Super Contributor
timestamp: June 26, 2024, 09:49:59 am
content: And since we're at it, take a bit of time to watch thisP.S.The only modification I'd make to that "hula loop" would be replacing the wideband preamp with a tuned one and adding a galvanic isolation transformer between the loop and the preamp, as for the latter, this one is pretty nicehttp://www.arrl.org/files/file/QEX_Next_Issue/Jan-Feb2018/Steber.pdfsince it will turn the loop into a "tuned" one (ok, not exactly, but ...)

author: Geoff-AU
author_rank: Frequent Contributor
timestamp: June 26, 2024, 11:27:40 pm
content: The basic way the PA0RDT whip works is by being a very electrically short "monopole" (vertical) fed against "ground" (or a counterpoise). Then it has active amplification to make its low sensitivity usable.The active element is a rectangular patch (behaves similarly to a short vertical whip), and the counterpoise is either your coax shield or metal pole (or both). The counterpoise is doing a considerable amount of the receiving work.It's important to either earth-ground your coax shield, or put a common mode choke, where you want it to stop being part of the "receiving antenna" part of the system. Otherwise, the shield is still part of the antenna and will receive all of your internal building noise.Stainless cable ties will be fine if they wrap around the lower part of the mini-whip, where the amplification circuit is. Keep them away from the patch element. Nylon cable ties only last a couple of years exposed to UV.You might get diplexing to work, but I don't really like the idea because the mini-whip already is a bit fussy. Depending on where your common mode choke is, the coax shield side of the VHF antenna could end up being part of your mini-whip receiving system too.

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: June 29, 2024, 07:08:14 am
content: I hope you haven't bought one of the eBay "look alike" mini whips. The PA0RDT style active antenna is very easy to make, I have used one for several years and they work really well and cost little. This page describes how to make and install one.https://www.qsl.net/g4aon/pa0rdt_aa/SJ