I've had questions about my antennas, how they are set up and what I do to reduce noise and RFI pickup as much as possible. Hopefully this will be interesting, and perhaps useful to others. Questions, comments, and any suggestions or notes about things you've done to improve reception and reduce RFI are certainly welcome!
Currently I have the following antennas:
670 900 ft sky loop
43/48m folded dipole
Two 20m folded dipoles
10/11m folded dipole
11m vertical dipole
250 ft V Beam aimed northeast
500 ft mini beverage aimed northeast
300 400 ft mini beverage aimed south
270 ft mini beverage aimed west-southwest
Crossed Parallel Loop (2m by 2m active antenna)
Discone antenna for VHF/UHF
1000 ft Loop on Ground (LoG)
I have a 75m dipole presently under construction
Update:
The 75m dipole is up, but presently in more of an inverted vee configuration
Also two LoG (Loop On Ground) antennas: One is 350 ft perimeter, the other 50 ft
Another update:
The Crossed Parallel Loop is now a passive antenna, the LZ1AQ amp having died. The AFE822x has enough front end gain that it works fine passively.
The 75m dipole is gone. It never worked well.
The 50 ft LoG is also gone, the 350 ft LoG is now a 950 ft LoG. It works exceptionally well on MW and LW, as you might guess.
New to the antenna farm is a 58 ft T2FD, which works exceptionally well, given the small size. Details here:
https://www.hfunderground.com/board/index.php/topic,56285.0.htmlUpdate: The 10m dipole was rebuilt as a folded dipole:
https://www.hfunderground.com/board/index.php/topic,60474.0.htmlAnd another update, now also a larger 120 ft T2FD:
https://www.hfunderground.com/board/index.php/topic,60665.0.htmlYet another update: Two new 20 meter dipoles, separate post to follow about them. Also the discone was moved to another tree and raised higher, see:
https://www.hfunderground.com/board/index.php/topic,61347.msg211568.html#msg211568All of these antennas are fed via coax cables, with the exception of the Crossed Parallel Loop, which is fed by shielded CAT5 ethernet cable, which also provides the power and control signals. One pair of the CAT5 is the return signal.
All of the antennas fed by coax have either a balun (for the dipoles and sky loop) or an unun (for the beverages). The baluns are standard commercial ham units, the ununs are my Squid Universal Matching Transformer, which I sell if you're interested:
https://blackcatsystems.com/rf-products/matching-transformer-unun-balun-beverage-longwire-k9ay-flag-ewe-dipole-antenna-shortwave-ham-radio.htmlThe advantage of the Squid is that it has multiple taps, allowing the best impedance match to be selected.
A brief description of the antennas:
The 670 ft sky loop is my "workhorse" antenna. I use it for general listening, and it feeds both the netSDR (on which I run overnight recordings of the 43 meter pirate band) as well as the KiwiSDR which I have online:
http://sdr.hfunderpants.com:8073What can I say, it's a great antenna. Excellent from the middle of the MW band up through about the middle of HF, say 19 meters. It does work on the lower end of MW, but is not as sensitive due to being too short there. And it's deaf on LW, again due to being only a fraction of a wavelength long. It does pick up signals on the upper end of HF, but it's really way too long there. But it's super sensitive on 43 meters, right where I use it the most. Picks up super weak pirates from South America. It has been patched over the years, I've had trees fall on it and pin the wire to the ground. And couldn't tell from the performance, only when I looked out my window did I know it happened. There is nothing magical about the length, it's just wha I was able to easily fit. Roughly it works down to where it is about one half to one third of a wavelength. So keep that in mind if you're building one. On the high frequency side, there is no hard limit, the performance just starts to drop off as it becomes many wavelengths long. I suspect it has a rather weird pattern especially on the higher bands, with lots of peaks and nulls.
The antenna is roughly 4 sided, although there are some bends in it, 670 feet in total perimeter. The hight varies depending on the trees used, generally 20 to 50 ft high. It is fed with a 4:1 balun to RG6 coax, which is what I use exclusively. Life is too short for dealing with soldering PL-259 connectors. I recently switched to using compression F connectors instead of crimp, which has been a life changing event. So much better.
Next I have the 40, 20, and 10 meter dipoles. The 40 meter is a folded dipole, built with 300 ohm ladder line and fed with a 4:1 balun. The others are traditional dipoles built with regular wire and 1:1 baluns. The 40 meter dipole is sloped, the low end is maybe 6 ft high. The others are mostly horizontal, as high as I could get them. Maybe 40 or 50 feet?
The beverages run about 6 to 8 feet above the ground. As mentioned above, each is fed with a Squid Universal Matching Transformer. The antenna is connected to one of the transformer taps, and a local ground rod to the other. Then the output is fed with the RG-6 coax. So the input and output of the transformer is isolated. Each beverage is terminated into about 300 ohms. I am considering removing the termination from the NE beverage as it seems to have affected DGPS reception. But the South beverage also terminated and works great. So I am not sure exactly what is happening. These antennas of course are very short at DGPS (300 kHz) and should not be considered real beverages on that band. Who knows what the actual antenna pattern is like.
The Crossed Parallel Loop is an active antenna, built using the LZ1AQ amplifier.
A previous post about the Crossed Parallel Loop:
https://www.hfunderground.com/board/index.php?topic=38963.0My blog post about building it:
http://www.radiohobbyist.org/blog/?p=2340On LW and MW, it is directional, and I get pretty good nulls. On HF of course you can't really get a decent null and it does not seem to be very directional. It does not perform as well as any of my full sized antennas, but it is close in some cases. I actually think this would be a great antenna for anyone with limited space, and cannot put up full sized dipoles or a large sky loop. The antenna is mounting on a iron pipe that is anchored in the ground in poured concrete. There is also a rope that goes from the top of the antenna up over a tree limb, which takes some of the weight.
In the distance you can see the frame for a large longwave / medium wave loop antenna that I experimented with some time ago. Not sure if it will come back or not. The wire for it ended up in a beverage antenna:
https://www.hfunderground.com/board/index.php/topic,36639.0.htmlFor VHF/UHF I have a discone antenna, which is way way up in a tree. Hey, it works. Pretty well, actually. It's got a Radio Shack "satellite" pre-amp/LNA that is rated for 450-2500 MHz or so, but works OK even down on the VHF Air Band.
All of my feedlines (except two of the beverages) are buried. I dug trenches and ran 2" diameter plastic conduit. This carries the coax (and CAT5 for the Crossed Parallel Loop) as well as a piece of rope, so I can pull through more cable if I need to. Running underground serves three purposes. First, yes, it looks better. Second, the earth is lossy at HF, and can help to attenuate RFI/etc flowing on the coax shield. And third, it may be safer from a lightning safety point of view. I have three conduit runs to different locations of the yard.
The coax for the south and west-southwest beverages is not buried, but runs just above ground level along a fence line.
All of the coax cables are grounded at multiple points. At each end of the underground conduit run for the buried cables, and at the ends and several intermediate points for the two beverage runs at ground level. Why? At RF, a ground connection is only at ground potential for short wire lengths. Once the length becomes a large fraction of a wavelength, the impedance of the cable is no longer close to zero. So the opposite end of the wire is no longer at ground potential. Grounding at multiple locations helps to alleviate this. I also have a ground wire run buried alongside one of the conduit runs as a sort of ground radial, and plan on adding it to the other conduit runs. More grounds is more grounds.
To ground the coax cables, I make heavy use of satellite TV grounding blocks. I got a bag of 25 of them (dual inputs) for just $16 on eBay. Each is mounted on a metal rod driven into the ground. At the shack end of the runs, there is an additional connection to my multiple ground rod system of several parallel connected rods.
From the shack side of the cable runs, the cables go up the side of the house and enter the second story shack to my Patch Board, which is an array of BNC jacks. It lets me connect any antenna to any radio. There's also a pair of jacks to my antenna tuner. I have a homebrew longwave low pass filter that I use when decoding DGPS, as well as a homebrew splitter, which allows me to feed both the netSDR and KiwiSDR from the sky loop. Another thread about the patch board:
https://www.hfunderground.com/board/index.php/topic,41737.0.htmlThe coax cables from the patch board to some of radios (the netSDR and AFE822x) are wrapped around some large toroid cores, to help reduce any RFI on the shields.
Whew. I think that's about it.