PA0RDT mini whip active HF antenna

 

When M0XDK first asked my opinion on the PA0RDT mini whip design I told him I had no idea how it could possibly work. I think “snake oil” may well have figured in my reply. I didn’t put him off and he put one together from junk box parts. There were probably too many substitutions as it showed more promise as a jammer than an antenna being very unstable and oscillating at the slightest provocation. He bought a kit of parts from an eBay seller and was impressed with the result. Naturally when I looked the seller had no more on offer but I was able to find a kit of parts sold by WA3IAC Chuck Steer as eBay seller chuckwa3iac. Well after building mine and doing some initial testing which has unfortunately been brought to a premature end by a mishap with my FT817ND power connector which I won’t be able to fix till I get back home I still have no real idea how this design works but it certainly does. From the WSPR trials I did manage to do it was between 2dB and 7dB down on the 20m loaded whip I’m using for WSPR here at my holiday caravan on 20m and a few other bands using an LDG Z 817 QRP auto antenna tuner whose testing too will have to wait a while now. Now 7dB down on an antenna that is already down by no doubt a fair bit on a dipole isn’t world shattering until you consider it is less than 30cm total size and covers from MW to at least 30MHz and possibly more. I’ve been impressed enough to order another kit to mount at home.



PA0RDT whip assembled circuit board

Assembled cicuit board with short additional whip soldered on.

PA0RDT whip circuit board in plastic trunking

Circuit board with a block connector for the coax inserted in a short length of white plastic cable trunking I had to hand. Some pieces of foam packaging are used to hold it in place.

Power injector circuit board for active antenna
The active antenna kit also included a power injector board. I’ve added connector blocks to that and mounted it in a short length of white plastic cable trunking along with some more pieces of foam packaging to wedge it in. As there is no strictly defined impedance I’ve used some TV cable and F connectors on both this and the antenna itself with a PL259 UHF connector for the receiver rather than 50 ohm cable simply because I had some to hand.

PA0RDT active antenna ready for initial testing

This is the assembled antenna section ready for initial testing. The short pieceof copper wire in this version is poked through the self amalgamating tape top seal. I decided to shorten the extra whip to avoid the reduction in water tightness in the version mounted on the caravan.

Power injector circuit board for active antenna in plastic cable trunking

PA0RDT whip mounted on caravan antenna

This is the antenna mounted on my caravan TV aerial. I have found that the TV antenna is not grounded to the van walls and roof so will be running the earth wire which is currently under one of the TV antenna mounting wing nuts down to a gutter screw as was done for the 20m loaded whip.

Unfortunately the FET blew just before end of the caravan season so I’ve had to bring it home for repair. I’m not sure if this was just bad luck or is going to happen regularly – time will tell. If it does happen again then I may put a 1 meg resistor from gate to ground to bleed off any static that builds up. Testing will resume about April 2015 when we start using the van again. I have built the extra kit for use at home but haven’t got around to installing it yet – there are a number of outstanding antenna projects and it looks like I’ll need to drill yet another hole through the wall to accommodate the cables. I’ll take the opportunity to bring the weathercam feed in with RX antennas only as just the 120mW my WSPR beacon generates is producing some severe interference on it.



  13 Responses to “PA0RDT mini whip active HF antenna”

  1. On S-metre FT-767GX level noise fell with 7 before three, on 40 metre ranges.
    The Attenuator 20дб is unplugged.
    Passage on SQ presently practically is absent, very bad

  2. I have no idea what the above comment actually means but it looks like a bad report and isn’t spam so I’ve approved it.

  3. The 2nd line says that the 20db attenuator was unplugged. I have no idea about the rest but PA0RDT stuff is usually absolutely spot on.

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