Active preselector + YouLoop?

[ka3jjz]

I've almost settled on getting a Tecsun H501x shortly - but what to do for an antenna? A loop is an obvious solution, seeing I have a HOA and live in a condo. (and no, I can't put anything outside - too many kids running around). i do have an old Palomar active preselector in my closet that might be a starting point, though

In an urban environment (I live some 8 miles from the DC border), active preselectors are usually things to avoid. There's already a ton of RF in the area, and increasing the noise level is also a consideration. Even putting an active amp on a loop like the LZ1AQ might cause issues. But....

If I built a YouLoop and fed it to the Palomar, then into the H501x, it seems that this might do the trick. The Palomar is tuned, has a battery for power, and the gain is fully adjustable. It would almost certainly be a whole lot cheaper than a AOR LA400 (don't even look at the prices on fleaBay if you have a weak heart). It would also be cheaper than the W6LVP experimenter's kit (which is my second choice). The Palomar is in my storage closet somewhere, so the cost here is quite small.

If you see an active preselector like the Palomars, the Radio West (Kolb / Sanserino) or the MFJ offerings in a used list or hamfest this might be a way to go if you are in a similar situation.

As soon as I gather a few things up, I will report back. Any comments are welcome....Mike

 

[ab3a]

I have lived in this region most of my life. Believe me, I sympathize with your dilemma. I have a PL-680 that I take with me when I'm camping or when I am headed to a rural area. Doing much HF listening near a city like DC is difficult. And don't think it's just switching supplies and all that. DC has some terrible RF density from some of the weirdest and off-normal stuff you can imagine. I can tell you all sorts of interesting stories of odd things we have seen on the air.

When you build your YouLoop, you should do your best to keep it balanced. The commercial one you can buy from rtl-sdr.com or YouLoop HF loop antenna – Airspy.US are pretty good and you can't beat the price. I hang one in a window near me and feed it to an HF+Discovery with Spyserver running on a Raspberry Pi4.

The HF+Discovery is very sensitive, so I don't really need a preselector of any sort and I don't live near any major radio stations. But you probably will. So I'll be interested to see some feedback from you on how well it works.

 

[vagrant]

It looks like a good plan, although I am not familiar with the Tecsun. Anyways, you already have the preselector and can adjust the gain. When you null the noise with a loop (hopefully), a little gain can sometimes help.

I just remembered that I have one of those Realistic 20-280 active preselectors. I previously tested it with that store bought Youloop and it does increase the gain after a null of the noise, as it should. Still, with that Realistic one it must be turned on if it remains inline, versus a passive preselector.

 

[ka3jjz]

Yes, a lot of folks think that running an active preselector at 100% gain all the time is the answer. Nope - you could induce overloading and introduce more noise issues. The max you should ever set this would be at the point the AGC clamps down and/or where the noise starts to increase. That is very dependent on the radio - a desktop like, say a Drake R8, is going to be more tolerant to this than a portable. It will be an experiment and a good way to learn about the front end of the Tecsun....Mike

 

[merlin]

I suppose I will start with some basic 'rule of thumbs' for HF/MF
>Mag loops are very worth considering, many in your shoes install them in attics or veranda.
DIY youloop, construction can be quite critical unless you can closely clone commercial loops.
>Gain/loss: you need the least amount of noise possible. The lower the noise,, the better the sensitivity.
>Amplification: Sadly at HF/MF frequencies, gain increases noise in proportion to signal.
too much just makes bad even worse. Get the best S/N ratio you possibly can.
A word about preselectors: My observation is most(all) are really not that. that simple tuner hardly 'selects' bandpass.
Many lack attenuation or bandstopping and that part really helps. In example, my best SWL preselector >>
1>first stage is tunable trap/bandstop. with bypass.
2> second stage is tunable bandpass/low pass/high pass
3>third is gain amp, 0 to +21Db, with bypass. (really does little more than compensate for filter loss.)
4>Decade attenuator, 0 to -30Db with a post 2Db attenuator to help coupling.
Back to the loop, I have been eyeing the MLA-30 loop. You don't have to spend lots of money for a good loop.
this will likely be installed in shack, or a small rotator, maybe just above the roof.
The Davitu Module Board is another option.
I have several "high end" receivers, for now, an HF/MF/LF SDR and Icom IC-R71A
(a lot of stuffing for my tiny shack)
PS: that W6LVP loop is very well worth considering, I am not ruling it out.
73s

 

[ka3jjz]

Actually the Palomar I have is pretty good with out of band rejection - here in the DC metro, I'm expecting to have issues. So I'm going to need all the help I can get - particularly since I am going to be using a portable. Even the H501X might have issues with all the FM and TV crud. Filters being installed are not out of the question. It's just a portable, after all

As I understand it, the original MLA30 uses a broadband video amp - something I need to avoid at all costs. I'm unsure whether the MLA30 plus has the same amp. Also this Facebook group might be interesting if you're serious about getting a MLA30 model...

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Mike