Re: HF+ problem below 300kHz - Alpha signals [SOLVED]


D R
 

Hi Patrick,

See the attached photos of what I did to R3.  If I want to return it to its original state I can just cut the bottom of the U, then put a blob of solder across the cut to re-shunt it.  Adding a switch would be easy enough, but I'd like to keep the nice box intact.  I suppose all mods are carried out at owner's risk, but anyone with a decent soldering iron and a modicum of skill can safely do this one.

When I got mine I did a quick comparison against the ELAD S2 and they were pretty much on a par down to the NDB band, where the S2 was rather better, and the MSF time signal on 60kHz was well below the level on the S2.  At the Alpha end, 11 - 15kHz, there was absolutely nothing on the HF+, although they were easily seen and heard on the S2 and (to a lesser extent) the RSP1A.  I didn't look closely enough to judge exactly where the S2 and HF+ started to diverge, but it probably started just below MW, and they were well separated below the LW BC band.  After the mod, however, the results speak for themselves - the HF+ is now quite a bit better than the S2 in the VLF range, and its equal in the NDB band (and probably on MW and HF, but I haven't done any comparisons myself to test other frequencies after the mod).  For anyone interested in VLF, the R3 mod (if it can even be classed as such) is what would currently be termed a "no brainer".

I've also attached another couple of screenshots to show the HF+ / S2 comparison today.  Have fun with yours when it arrives.

Regards,
Dave



From: Patrick <aunumero73@...>
To: main@airspy.groups.io
Sent: Monday, 8 January 2018, 8:51
Subject: Re: [airspy] HF+ problem below 300kHz - Alpha signals

Hi Dave,

<< The R3 capacitor is nowhere near anything else, and soldering a bridge across it takes only a few seconds >>
It would be nice if someone could post a "How to" with some pictures or a video for non-technie users. Keep in mind that some SWLs have no skill at all for this, even if it looks like the easiest thing to do for you !
What about the warranty is the unit is modified ?

BTW, what is lowest frequency where the HF+ shows its 'normal' sensitivity ? This thread states 300, does it mean that LW stations are affected or only frequencies below 100 Hz or so ?

Have a nice day !








2018-01-08 0:51 GMT+01:00 D R via Groups.Io <robsond90@...>:
There's no need to be concerned about opening it up, Patrick - there's very little inside except fresh air and a little bit of fairy dust.  The R3 capacitor is nowhere near anything else, and soldering a bridge across it takes only a few seconds.  You won't hear a thing below 50kHz without doing the little mod.

Regards,
Dave



From: Patrick <aunumero73@...>
To: main@airspy.groups.io
Sent: Sunday, 7 January 2018, 22:50
Subject: Re: [airspy] HF+ problem below 300kHz - Alpha signals

<< Like one or two others, I wasn't pleased to find that the HF+, as delivered, is stone deaf at VLF when used with a 50ohm antenna.  However, following prog's advice to bypass R3, I placed a crocodile clip across it and the difference was staggering >>
I'm worried to read that the HF+ has to be modified when using a 50 ohms antenna to get its full potiential  on LF/VLF ...
I don't intend to open my unit though when it arrives. We'll see how it behaves with my ALA1530 and the mini-whip.






2018-01-07 21:39 GMT+01:00 D R via Groups.Io <robsond90=yahoo.co.uk@groups. io>:
Like one or two others, I wasn't pleased to find that the HF+, as delivered, is stone deaf at VLF when used with a 50ohm antenna.  However, following prog's advice to bypass R3, I placed a crocodile clip across it and the difference was staggering, as the dead zone below 50kHz immediately came back to life.  A quick scan of the NDB / MW / HF bands up to about 20MHz revealed no obvious impact above VLF so the clip was replaced by a piece of U-shaped hookup wire soldered across R3, which can be easily removed or cut if the need arises.

I carried out a comparison between the HF+ and the ELAD S2 using a Wellbrook LFL1010 antenna, and you can see from the attached screenshots that the HF+ is the clear winner (which surprised me, as I thought that the S2 would have had the edge).

I intend to make one of Mendo's filters to see how it performs, but there's no doubting that bypassing R3 actually works, and works very well (and only takes a couple of minutes from start to finish to carry out!).

Regards,
Dave




From: Mendo Mendevski via Groups.Io <germanikos=yahoo.com@groups. io>
To: main@airspy.groups.io
Sent: Friday, 5 January 2018, 20:57
Subject: Re: [airspy] HF+ problem below 300kHz

For best results in receiving VLF and LW frequencies with Airspy HF+ I am using homemade 9 pole Low pass filter (fc=530 kHz)
The performance is much better without IMD from AM Broadcast stations.

You can see this link for my LPF:  Mile Kokotov LPF_530kHz




Mile Kokotov, Z33T


On Friday, January 5, 2018 9:46 PM, Patrick <aunumero73@...> wrote:


That's intesting because I'm a NDB DX'er (and regularly tuned to VLF/LF frequencies).
Also own an ELAD S2 + mini-whip and ALA1530LN loop.

Still haven't received my HF+ to test in this range.



2018-01-05 21:40 GMT+01:00 Aldo <iw2dzx@...>:
>
> Your antenna might be not well matched in the LF with the HF+. Can you test
> with a mini-whip?

I place a Miniwhip (4 mt. high only) for test.
http://www.iw2dzx.it/BC/ Miniwhip.jpg

No Alpha signal on HF+ and low SNR from MSK stations.

73
Aldo









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