New LZ1AQ commercial amp and dual loop antennas.
edited August 2018 in Installation, Antennas and Interference
I bought a commercial version of the LZ1AQ amplifier a while back and just got around to putting it in service. It is running at http://ka7u.no-ip.org:8074 . I like it, but it has about the same gain as my 210' top dipole and so 1260 and 1380KHz stations are up above -20dBm and OV the kiwiSDR. I think it will be worth wiring up a couple of filters to attenuate those 2 stations and so that is the next project. The DIY LZ1AQ amplifiers work quite well and they don't have enough gain for these broadcast stations to overwhelm the KiwiSDR, but I never connected 2 loops to them either. I might give that a try and then I might be able to see just what I gained from the commercial version versus the home built models. I am very impressed with the quality of the LZ1AQ commercial amp.
Sounds like you have the space to try four crossed loops, the info on building antennas seems to imply that is a very sensitive antenna for quiet areas.
Your site has an enviably low noise level so I'm guessing that would do the trick.
Ron - KA7U
My use of old push bike wheels for the loops was just a hunch after trying various aluminum lying about and trying to get an idea of the best trade off sensitivity to noise, I must compare it to something larger in a quiet location, here they do OK and anything larger would be a waste.
I did (recently) try loops at 90degrees but can't remember them working well with this "98% from one direction QRM", didn't try for long so you may tempt me to revisit when next playing aerials.
I have a second LZ1AQ amp, want to put that up at the works QTH assuming I can with low risk to the company kit and finding somewhere to hide the loops.
I haven't decided which antenna to connect to the Kiwi (assuming it eventually arrives from MassDrop) but it might be this one. The other choice would be the sky loop which is the best overall performer, but I am not sure I want to lose a few dBs from a splitter. I rely on it for my overnight netSDR recordings.
Also adds some level of surge and over power protection. I realise they aren't cheap but at least it should allow you to keep your existing recording setup without any degradation and add other receivers at any time.
I considered one but then remembered as space it tight and I run only small antennas a second LZ1AQ would be cheaper.
I started out with intention to use a clear top junction box
but while considering dissimilar metal corrosion I remembered I'd also ordered a larger enclosure that may keep most electrical connections inside, I decided to temporarily use that while I working out the external connector layout for the original box (dependent or orientation and ease of inspection/rework).
The element wiring exits out the back of the box through four M6 machine screws and lugs driven by the enclosure layout (same as the original box in one dimension, shorter in the vertical) I have two 6mm nylon plates behind that, the idea was to have a test base I could swap out elements without too much risk to the PCB, I also wanted the bike rims to be self supporting if I have it horizontal.
I do still want to work on the clear top enclosure as it is neater but this should hopefully survive the winter and I can swap the current rims out for something larger.
I used a 4mm banana plug socket for the drain wire and an overly expensive (Bulgin?) waterproof RJ45 housing from the work junk pile, I've since found more reasonable RJ45 connectors on Ebay/Amazon.
I'll put another spade crimp socket on the CAT5 connector shield so I have the choice to earth through the shield or separate wire.
Right now it is screwed to the fence, I had to think about that, ended up with the nuts on the back so I remove the back nylon plate screw that to the fence then bolt the box+rims to that, not very good solution as things flex while the back plate is off and kept the holes close to bolt size, but this is just a way to test mechanical ideas and get back into CAD (Sketchup for now) which I used to quite enjoy.
A nice build :-)
A couple of observations, sorry if I sound a bit picky (I know, just can't help it), but I've learnt from past experience and a lot of rusty water..........
You will get water ingress via the loop mounting bolts where they pass through the plastic case. Anything passing through the top or sides of boxes mounted outside like that will let in water.
The only way to avoid this is to either use a box within a box (the outer as a rainshield) or put all the connectors and cable passthoughs on the bottom face of the box.
Condensation is another problem. It will probably be OK if the LZ1AQ amplifier is powered at all times as the heat will help keep it under control, but personally I'd drill a small hole approx 3mm diameter in the bottom face of the box to let any condensate evaporate / drip out.
For general information purposes, you can get better use of switched loop directivity / nulls if the two loops are mounted at right angles to each other rather than in the same plane, but I guess you knew that anyway. Otherwise you may get better S/N in loop mode by just connecting the two loops in parallel rather than having them switched.
Martin - G8JNJ
It can be so bad here it's like trying to work out if it is 85% noise or 89% noise.
I'll leave it connected for a long enough to affect the graphs at http://sibamanna.duckdns.org/sdr_map.html then change some things.
These rims are 58cm Diameter some 8% less diameter than the others so losing some sensitivity is expected.
Yes I was going to drill a hole on the bottom and seal the bolt entries with silicon once I'd run it for bit in case the layout, long bolts, penny washers made it worse.
I don't like the huge box for home but need something small (antenna size)and low value to hide at work, camo paint is next.
The enclosure has some deep lugs where the bolts go through so the water would have to wick along the threads a fair way, so that should be sealed OK with (non acid) silicon I assume.
That was one of my concerns on the other enclosure, didn't want to route wires to the bottom and back up also wanted a dipole option so suddenly lots of holes to seal depending on orientation.
At the bottom is the waterproof CAT5 socket and the ground socket both plastic and solid body I could stand about 10mm of water before it hit anything.
It's a good point about right angling one loop, I've spent so long propitiating the null gods I will have to arrange some other way if I find the noise acceptable at another location. I have build it with a 25mm square route through the loop gaps so it should be trivial to extend on a 25mm fibreglass square tube ( I checked was available while assembling) and rotate one loop, does add back in connections but then I also want to try the four loop thing so that will also take some extra connections.
I'm glad I bit the bullet on these amps at they work better than others here and getting the drill and spanners out makes a change from screen "work".
I did the second amp with 700cc rims (covered in heatshrink).
I added a link earth socket to CAT5 shield for grounding route options.
Angled loop null as best I could for next door, buried the CAT5 and earth drain wire (for about 2m).
Obviously more sensitive with larger loops but the usual interference was pretty bad, spent some time with noise blanker and others tweaks but I noticed rather than peaking at 7MHz with affects seen at 25MHz+ it seemed to be slightly less sharp but visible across hf.
Played with modes and the dipole mode was not as bad as before (very strange) so tried loops and hit a switch combination that seems to turn the noise off, I can currently listen to HF here.
I did spend some time getting the element feed wires the same length and both the shield routes are connected but, for whatever reason with these loops, in this mode and alignment right now I have nulled my main source of interference. Not going to disturb anything and will record feed length and everything else tomorrow as I've been working on this noise issue for ages, I might have finally hit a workable combination.