HFU HF Underground
Technical Topics => Equipment => Topic started by: ChuckConner on June 20, 2016, 2303 UTC
-
A Russian ham, RA0SMS, is selling a mini-whip active antenna on "the" auction site. His version appears to be similar to the PA0NHC design. The PA0NHC design apparently contains improvements over the original PA0RDT design. The RA0SMS model is cheap ($37 assembled with free shipping) and he has lots of good feedback. I've been considering buying one but would like some additional opinion. I'm hoping someone here may know more about it. Thanks!
-
Hello Chuck,
I own both antennas the PA0RDT & RA0SMS.
Please take look at this topic: http://www.hfunderground.com/board/index.php/topic,22537.0.html
If I compare my PA0RDT vs the R0SMS, there is not much difference in performance. The P0RDT kit seems to perform slightly better.
For $37 you can’t go wrong in my opinion. On the other hand RA0SMS does also offer a $15 DIY Kit for the Mini Whip, if you rather build one yourself.
The PA0RDT is also as DIY Kit & assembled Version available on fleabay.
Good luck and maybe you can provide some feedback once you have one of the antennas installed.
-
Thanks for that information, I will order one. Too bad it may take up to 2 months for shipping!
-
If one is interested in rolling their own active, here's a good one;
http://home.earthlink.net/~christrask/Complementary%20Push-Pull%20Amplifiers.pdf
-
I agree with Josh. Short verticals with the complimentary output stage amp can give excellent performance, depending on what freq range you are DXing. Mini-whips with lengths between 3 and 10 feet are one of the commonly used antenna types for NDB DXers in the 200-500 kHz range.
I use an active mini-whip for LF NDBs in conjunction with a resonant loop; they are very complimentary antennas. I have used it with whips from 36-72", but tend to keep it at the shorter 36". It also works well into HF.
-
Oliver,
Did the mini whip from RA0SMS come with a power supply? And is there any need to convert it to take 60 Hz AC? He's in Russia where AC is 50 Hz, that's why I ask. His listing doesn't say and I figure I'd rather ask someone who's using it already.
Thanks!
-
MDK2,
yes the antenna came with the power feed unit.
All you will need is a 12V source.(I made my own adapter Pic. 4 chinch to dc jack).
His updated version has a different housing / modified power feed unit.
As shown in (Pic. 1-3) all antenna connectors are BNC.
Depending on your setup, you may need some adapters to PL 259 or what ever connection you desire.
You can find several videos of the Mini Whip on his website.
http://ra0sms.blogspot.de/p/video-antenna-miniwhip.html
Here the ebay link:
http://www.ebay.com/itm/Mini-Whip-HF-VLF-active-RX-antenna-10kHz-to-30MHz-with-RF-isol-trans-/201576908470?hash=item2eeeeb86b6:g:48cAAOSwxp9W5sSA
-
Thank you very much Oliver! That's all extremely helpful.
-
It appears the 1:1 isolator is integrated into the voltage injector, thus the antenna likely is relying upon common code currents on the feedline as part of the antenna. It is a common approach with small active antenna designs, and like many of such designs, a good RF ground probably will help. Likewise, if incurring increased noise, try improving RF grounding and/or moving around the voltage injector to another location if possible.
-
As the OP on this thread, I thought I would give you an update on my experiences with the RA0SMS mini-whip active antenna. I actually ordered two of them because I have an antenna phasing unit and wanted to try some phasing experiments with them. My order arrived in only two weeks – much faster than I expected! Unfortunately, I haven’t been able to mount them properly (high and far from the house) yet. My first experiences were with them located indoors (bad idea!). I’ve been battling RFI for some time now in my listening area. I use common-mode chokes and a galvanic isolator on the antenna lead-in. The antennas are definitely sensitive to local RFI sources as expected, they make great RF sniffers! I briefly moved one outside (onto a wood fence) and compared it to my indoor mag loop antenna. The station signal levels were similar but the active was still picking up RFI (from somewhere) pretty well! The receiver noise floor when using the antenna is fairly low – can be higher or lower than the mag loop depending on the frequency. One interesting (bad) thing I discovered with the active antenna was the presence of images from a strong local AM station on 1230 Khz (1 KW, 1 mile away) – these were at harmonic frequencies (e.g. 4920 and 6150). Those are not seen with the mag loop so I am calling them images. I hope to get at least one of the mini-whip antennas mounted outside better in the near future. With proper installation and grounding, I’m sure they could be a reasonable choice for someone with limited real estate and/or finances. Hopefully I will have more information to share later.
-
Thanks for your review Chuck. I got one a few weeks ago (asked for it for a birthday present), and it only took about two weeks too. I haven't been able to do anything with it as of yet, other than plug it in to make sure it works (lots of RF indoors as you say). I need a mount and think I may get a telescoping fiberglass mast so that I can get it up as high on above my roof as I can. I'm limited to 40' per zoning but can probably get away with a few more. I have to get up there with one of the portables in order to see what the RFI situation is like. I'm not in much of a hurry because our swamp cooler is on the roof and has proven to be a great RFI generator, so I will not really get to use it until September or so. I still have my homebrewed loop and random wire to tide me over til then.