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locked VLF Reception

D R
 

Anyone wanting to test their VLF reception can now do so at the bottom end of HF+ range again, as the Russian Alpha navigation signals are now back on air after a near four month shutdown.  The 11.90, 12.65 and 14.88kHz signals are coming in well in the UK at the moment.

Regards,
Dave

Dana Myers
 

On 5/10/2018 11:37 AM, D R via Groups.Io wrote:
Anyone wanting to test their VLF reception can now do so at the bottom end of HF+ range again, as the Russian Alpha navigation signals are now back on air after a near four month shutdown.  The 11.90, 12.65 and 14.88kHz signals are coming in well in the UK at the moment.
Several months ago, I cobbled-together an e-probe antenna and had good
results with VLF reception here in California. I did the 'R3' mod (100nF cap
piggybacked).

Recently, on a whim I connected my 25-1300MHz discone antenna to the HF
port. Without doing an A/B comparison, I can't say for sure, but I think it
works essentially as well as the e-probe did (and is less prone to overload).

I'll take a listen for the Russian Alpha stations this evening.

Cheers,
Dana

Alan G4ZFQ
 

Anyone wanting to test their VLF reception can now do so at the bottom end of HF+ range again, as the Russian Alpha navigation signals are now back on air after a near four month shutdown.  The 11.90, 12.65 and 14.88kHz signals are coming in well in the UK at the moment.
Dave,

Thanks, I'd almost given up looking.
My HF+ does have the R3 mod. The only reception I get is on my discone, so I'd suggest anyone tries any "stupid" antenna they have.
(I've also tried my Wellbrook, various wires, dipoles, e-probes, vertical to simulate the discone's situation and receive nothing there.)
The discone also did very well on SAQ hearing the carrier leakage before they started keying. Surely I can make something better...

73 Alan G4ZFQ

prog
 

On Fri, May 11, 2018 at 03:35 am, Alan G4ZFQ wrote:
The only reception I get is on my discone, so I'd suggest anyone tries any "stupid" antenna they have.
Not uncommon. Good HF antennas are in general poor in the VLF band. In the other hand, the NF of the HF+ is so low that a small whip would work just fine and without modding anything. Just make sure you are not contaminating your antenna with your own noise. Leif posted a series of videos about this topic, so I invite everybody to check his YouTube channel: https://www.youtube.com/channel/UClmNy6VRE1YqOeBHwb3o0Yg/videos

FYI. The newer HF+ batches have a 4.7 nF coupling cap in the HF path and the RF front-end was programmed accordingly. This helps getting a better impedance matching with some antennas like the active loops/mini whips. Other antennas should work the same.

D R
 

Hi Alan,

You were hearing Krasnodar and the double pulse from Novosibirsk in that recording.  Here's what they looked like on my HF+ and Wellbrook LFL1010 loop.

Regards,
Dave


On Friday, 11 May 2018, 11:35:13 GMT+1, Alan G4ZFQ <alan4alan@...> wrote:


> Anyone wanting to test their VLF reception can now do so at the bottom
> end of HF+ range again, as the Russian Alpha navigation signals are now
> back on air after a near four month shutdown.  The 11.90, 12.65 and
> 14.88kHz signals are coming in well in the UK at the moment.

Dave,

Thanks, I'd almost given up looking.
My HF+ does have the R3 mod. The only reception I get is on my discone,
so I'd suggest anyone tries any "stupid" antenna they have.
(I've also tried my Wellbrook, various wires, dipoles, e-probes,
vertical to simulate the discone's situation and receive nothing there.)
The discone also did very well on SAQ hearing the carrier leakage before
they started keying. Surely I can make something better...

73 Alan G4ZFQ




D R
 

Hi prog - would you recommend the 4.7nF cap in place of the short across R3 which I've had in place since early January, or would it not make much difference?  The short works very well with my loops, but every little extra is welcome.

Regards,
Dave


On Friday, 11 May 2018, 11:47:25 GMT+1, prog <info@...> wrote:


On Fri, May 11, 2018 at 03:35 am, Alan G4ZFQ wrote:
The only reception I get is on my discone, so I'd suggest anyone tries any "stupid" antenna they have.
Not uncommon. Good HF antennas are in general poor in the VLF band. In the other hand, the NF of the HF+ is so low that a small whip would work just fine and without modding anything. Just make sure you are not contaminating your antenna with your own noise. Leif posted a series of videos about this topic, so I invite everybody to check his YouTube channel: https://www.youtube.com/channel/UClmNy6VRE1YqOeBHwb3o0Yg/videos

FYI. The newer HF+ batches have a 4.7 nF coupling cap in the HF path and the RF front-end was programmed accordingly. This helps getting a better impedance matching with some antennas like the active loops/mini whips. Other antennas should work the same.

prog
 

On Fri, May 11, 2018 at 04:40 am, D R wrote:
Hi prog - would you recommend the 4.7nF cap in place of the short across R3 which I've had in place since early January, or would it not make much difference?  The short works very well with my loops, but every little extra is welcome.
 
Regards,
Dave
It depends. The general recommendation is: Do not change anything unless you know what you are doing.
So, I will suppose you already know how the front end filtering, impedance matching and the different AGC loops all act in concert to optimize your reception. Here's a table to summarize the ideal coupling depending on the (most common) scenarios:

Target band Small whip HF Resonnant Dipole Active Loop Active Mini Whip
VLF 300 pF - Not suitable - - Not suitable - 4.7 nF
LW/MW (AM BC) 300 pF 4.7 nF 10 nF 4.7 nF
Shortwaves / HAM 300 pF 300 pF 4.7 nF 4.7 nF

The cells marked as "not suitable" simply mean that the antenna will just "eat" the available dynamic range of the radio without improving the performance in the target band.

Chris Wilson
 

Hello Alan,

I sometimes use Martin G8JNJ's web based SDR which is a KiwiSDR. If
you go on his site you need to select "Antenna 5" which is a monopole.
I haven't looked at what it's like at VLF, but it's pretty keen on 136
Hz, and trying it costs nowt :) His web site has a lot of info on LF
and VLF antennas. Please be sure to reset the WebSDR to antenna 1 when
leaving, as the monopole is not much good on HF!

http://southwest.ddns.net:8073/?ext=ant_switch

I have not had much luck with an active mini whip on LF (136khz) so
use my resonant TX aerial for RX, into a Red Pitaya with input mods.
It seems to hear as well as most good UK set ups. What a well sited
mini whip is like on VLF I don't know, some swear by them, some swear
at them :)

Regards, 2E0ILY

Friday, May 11, 2018

Anyone wanting to test their VLF reception can now do so at the bottom
end of HF+ range again, as the Russian Alpha navigation signals are now
back on air after a near four month shutdown.  The 11.90, 12.65 and
14.88kHz signals are coming in well in the UK at the moment.
Dave,
Thanks, I'd almost given up looking.
My HF+ does have the R3 mod. The only reception I get is on my discone,
so I'd suggest anyone tries any "stupid" antenna they have.
(I've also tried my Wellbrook, various wires, dipoles, e-probes,
vertical to simulate the discone's situation and receive nothing there.)
The discone also did very well on SAQ hearing the carrier leakage before
they started keying. Surely I can make something better...
73 Alan G4ZFQ
--
Best regards,
Chris mailto:chris@...

Maurizio Marini
 

Hi Prog,

the 4.7 nF coupling cap is the new value of R3?
How do we understand if our AirspyHF + already has this change?
From the S / N?
(My s / n is 36529480D5343F93)

I use my own active loop and mini-whip on the MW and I currently shorted r3.
I would like to understand if it is more correct to put the 4.7 nF coupling cap on R3.

My interest in LW/MW.



Thank you,


Maurizio IW2GOB




Il 11/05/2018 12:47, prog ha scritto:
On Fri, May 11, 2018 at 03:35 am, Alan G4ZFQ wrote:
The only reception I get is on my discone, so I'd suggest anyone tries any "stupid" antenna they have.
Not uncommon. Good HF antennas are in general poor in the VLF band. In the other hand, the NF of the HF+ is so low that a small whip would work just fine and without modding anything. Just make sure you are not contaminating your antenna with your own noise. Leif posted a series of videos about this topic, so I invite everybody to check his YouTube channel: https://www.youtube.com/channel/UClmNy6VRE1YqOeBHwb3o0Yg/videos

FYI. The newer HF+ batches have a 4.7 nF coupling cap in the HF path and the RF front-end was programmed accordingly. This helps getting a better impedance matching with some antennas like the active loops/mini whips. Other antennas should work the same.

prog
 

On Fri, May 11, 2018 at 06:16 am, Maurizio Marini wrote:
I would like to understand if it is more correct to put the 4.7 nF coupling cap on R3.
As I said in my previous message: DO NOT change anything if you are not involved in designing RF front ends and know exactly what you are doing.
You will get better results if you avoid falling in the "not suitable" cases in that matrix - which means: Use the right antenna for the right band.

PS: The purpose of these public forums is not to educate people on how to design radios. It's an easy way for the designers to tell people how they should use the product. Ignoring the recommendations ALWAYS end up with a mess.