LF reception on HF+?


Andy <g1hbe43@...>
 

I don't yet own an HF+. I am thinking about getting one, but I hear several reports of images of MW signals in the LF range (below 400 KHz). I am asking because I want to hear what other users have noticed before I purchase. I know there is a recent hardware mod which has improved LF performance, but I would like to know the experience of others. Thankyou.


Alan G4ZFQ
 

t I hear several reports of images of MW signals in the LF range (below 400 KHz).
Andy,

I did the mod, a SMD component requires shorting.

I have not noticed any bad effects below 400KHz, indeed it seemed to work well on the Russian Alpha stations at 12KHz+/- (Are they on at the moment?)

I HAVE noticed problems using amplified antennas, but that is not the HF+.

Alan G4ZFQ


I am asking because I want to hear what other users have noticed before I purchase. I know there is a recent hardware mod which has improved LF performance,


prog
 

You can refer to these tests by Roelof PA0RT:

These tests also show that second order intermodulation from strong
signals at relative close frequency spacing is not easy to happen.
At my location, unlike other low cost offerings, the AIRSPY HF+ does
not suffer at LF from IMD from strong medium wave broadcast
stations.
https://groups.io/g/Perseus-SDR/message/27488?p=,,,20,0,0,0::Created,,airspy,20,2,0,8578805


Andy <g1hbe43@...>
 

Thanks Alan and Prog. I ask because I have tried other tuner-based SDR's and they have suffered from aliasing from MW signals. They all responded well to a 400 KHz LPF and worked well, but I'd heard so much about the HF+ it sounded tempting.
Alan - I can't get below about 17 KHz as my Wellbrook seems to roll off sharply around there.


Guy Atkins
 

Hi Andy,

HF+ owner and top MW DXer Bjarne Mjelde has summarized his recent findings here: https://app.box.com/s/d2dni57dzrsxgs38gxbbfz9gm26brqpk

With the simple mod and a firmware update the HF+ is extremely capable from MW on down,

73, Guy


Mark
 

Hi Andy

I purchased a Airspy HF+ and overall am very happy with it...even before I did the bypass mod and firmware update it seemed better than my SDR play RSP2.

Since the mod and firmware update sensitivity from LW and up seems far better than my RSP2.  And I have not noticed any spuri or out of band signals at all.  On the RSP2 in the NDB section lots of images would show up.

The only problem I have with the HF+ since doing the bypass mod is that down on LW and the NDB section I am getting interference from 100khz the Loran C transmitter at Anthorn about 50-60 miles from my location I use a mini whip on my balcony so it appears to overload the HF+  Once I tune to 530khz and up no more interference.  So only on LW and NDB area Before the mod this was not a problem.  I have a step attenuator inline and once I use about 20db it goes away pretty much.

So I am torn between removing the bypass mod and putting back to factory default or I may build a Loran C notch as described on Bjarne Mjelde website/blog.

As for software I have not really had much use with SDR# so am still learning it but even when I used the RSP2 I always turned to Simon Browns SDR console v3...for me its a winner all the way and its not even officially released yet !

The HF+ is certainly a very nice receiver and for the price it certainly packs a punch I have no regrets buying it

But if like me you will be using a active antenna and happen to be near a Loran C transmitter just maybe think twice before the bypass mode.  With a passive antenna I doubt it would be a problem.  If the Loran C was not such a messy transmission I doubt it would be a problem to the HF+ as it appears to handle strong signals exceptionally well for example the signal from radio 4 on 198khz end stops the s-meter on SDR console v3 put I don't get any interference from it.

Cheers
Mark
Southern Scotland


paul
 

I've picked up the 12kHz Alpha signals loud&clear with a triangular 1x1x1m indoor wire loop through a 9:1 transformer.
The HF+ is *very* sensitive down to a few kHz.
(R3 bypassed)
73
Paul


Alan G4ZFQ
 

I can't get below about 17 KHz as my Wellbrook seems to roll off sharply around there.
Strangely my discone gives the best reception of those stations, Wellbrook, "e-probes", wires either bad or not at all.

Alan G4ZFQ


Alan G4ZFQ
 

So I am torn between removing the bypass mod and putting back to factory default or I may build a Loran C notch as described on Bjarne Mjelde website/blog.
Mark,

Why not just use the attenuator?

Essentially that's all the shorted 300pF R3 is.

73 Alan G4ZFQ


D R
 

Andy,

The Alpha transmitters have been off for the last three days.  They were giving very good signals over the weekend but nothing at all from Tuesday.  In contrast, RDL in Archangel, 18.10kHz, was very strong today between 1230 and 1250, so the 14.88kHz Alpha transmission from Revda, at least, would certainly have been visible if it was on.  (I use a Wellbrook LFL1010 loop for VLF, which has no trouble in picking them up - especially with a modified HF+).

Dave



From: Alan G4ZFQ <alan4alan@...>
To: main@airspy.groups.io
Sent: Thursday, 1 February 2018, 17:16
Subject: Re: [airspy] LF reception on HF+?


> t I hear
> several reports of images of MW signals in the LF range (below 400 KHz).

Andy,

I did the mod, a SMD component requires shorting.

I have not noticed any bad effects below 400KHz, indeed it seemed to
work well on the Russian Alpha stations at 12KHz+/-  (Are they on at the
moment?)

I HAVE noticed problems using amplified antennas, but that is not the HF+.

Alan G4ZFQ


> I am asking because I want to hear what other users have noticed before
> I purchase. I know there is a recent hardware mod which has improved LF
> performance,








Andy <g1hbe43@...>
 

That's very interesting, Mark. I too use an RSP2. With a suitable LPF in front of it it works very nicely in the beacon and 'time signal' bands, very clean - but without a filter it is plagued with images. Funnily enough I don't get any problems with LORAN on 100KHz on my Wellbrook loop, despite living in the NW of England.
By chance, a friend has just been to see me and he brought his Colibri DDC sdr, a direct-sampler. Oh crikey. Very clean everywhere except for a spot of mild FM imaging when tuning around 10m and above. But of course it is about four times the price of the RSP2 and three times as much as the HF+. And of course the Colibri has no coverage above 60 MHz unless you are prepared to muck about with filters for the under-sampled bands.  Hmm. I think I'll sit & watch for a while. Thanks again.


Mark
 



Why not just use the attenuator?

Essentially that's all the shorted 300pF R3 is.

Hi Alan

My thinking behind the Loran C notch is hopefully it just attenuates 100khz and hopefully everything else is not affected .  because at the moment using the step attenuator does just about take the it away to remove it completely I am adding a lot of attenuation no good for DXing NDBs

With the factory default setting no interference but signals still seemed pretty good but yes from MSF 60khz down there was a massive hit to signals hence like everyone else I did the bypass mod.

without the problems from Loran C the HF+ handles the mini whip well.

Cheers Mark

 


Paul Higginson
 



>>Why not just use the attenuator?

>>Essentially that's all the shorted 300pF R3 is.


The capacitor in the position marked R3 isn't 'just an attenuator' at all, a 300pf capacitor at 100KHz has a series reactance of 5K which will significantly alter the input match at that frequency, depending on the behaviour of the amplifier in an active antenna this could be far from optimal. That same capacitor at 10MHz will add a series element of just over 50R.

Like many things in life one solution won't fit all circumstances, blindly changing values without considering the effect may not do what you expect.

73 Paul GW8IZR






jdow
 

A 100 kHz notch worth 20 dB would not be all that hard to make in a little metal project box. (A better box would be some copper-clad PCB with the joints fully soldered and a tight fitting top. But that's more work.) Heck, for 20 dB you might get away with simply using flying wire construction after cutting open a section of the feed line to access the center conductor.

{^_^}

On 20180201 11:01, Mark wrote:
Hi Andy
I purchased a Airspy HF+ and overall am very happy with it...even before I did the bypass mod and firmware update it seemed better than my SDR play RSP2.
Since the mod and firmware update sensitivity from LW and up seems far better than my RSP2.  And I have not noticed any spuri or out of band signals at all. On the RSP2 in the NDB section lots of images would show up.
The only problem I have with the HF+ since doing the bypass mod is that down on LW and the NDB section I am getting interference from 100khz the Loran C transmitter at Anthorn about 50-60 miles from my location I use a mini whip on my balcony so it appears to overload the HF+  Once I tune to 530khz and up no more interference.  So only on LW and NDB area Before the mod this was not a problem.  I have a step attenuator inline and once I use about 20db it goes away pretty much.
So I am torn between removing the bypass mod and putting back to factory default or I may build a Loran C notch as described on Bjarne Mjelde website/blog.
As for software I have not really had much use with SDR# so am still learning it but even when I used the RSP2 I always turned to Simon Browns SDR console v3...for me its a winner all the way and its not even officially released yet !
The HF+ is certainly a very nice receiver and for the price it certainly packs a punch I have no regrets buying it
But if like me you will be using a active antenna and happen to be near a Loran C transmitter just maybe think twice before the bypass mode.  With a passive antenna I doubt it would be a problem.  If the Loran C was not such a messy transmission I doubt it would be a problem to the HF+ as it appears to handle strong signals exceptionally well for example the signal from radio 4 on 198khz end stops the s-meter on SDR console v3 put I don't get any interference from it.
Cheers
Mark
Southern Scotland


Bjarne Mjelde <bjarne.mjelde@...>
 

The notch filter Alan was referring to is this: http://www.kongsfjord.no/bm/Notch%20Filter%20rev%201.pdf

It literally saved my DX. The Loran C station (now dismantled) was 14 km away, and I was pointing my beverages directly towards its 250 kW tx. It saturated everything within the bandpass.I made one filter for each beverage.
--
Bjarne Mjelde
World's Northernmost DX-er
arcticdx.blogspot.com
Arctic web-rx:  kongsdr.proxy.kiwisdr.com:8073


Billy Inglis <billyinglis49@...>
 

HI Mark, as there are a few of us thinking of purchasing the HF +, but are not too sure.
Why not do a review of the accessibility of the +.
We blind users would aprecitate such a rview, Billy

On 01/02/2018 19:01, Mark wrote:
Hi Andy
I purchased a Airspy HF+ and overall am very happy with it...even before I did the bypass mod and firmware update it seemed better than my SDR play RSP2.
Since the mod and firmware update sensitivity from LW and up seems far better than my RSP2.  And I have not noticed any spuri or out of band signals at all.  On the RSP2 in the NDB section lots of images would show up.
The only problem I have with the HF+ since doing the bypass mod is that down on LW and the NDB section I am getting interference from 100khz the Loran C transmitter at Anthorn about 50-60 miles from my location I use a mini whip on my balcony so it appears to overload the HF+  Once I tune to 530khz and up no more interference.  So only on LW and NDB area Before the mod this was not a problem.  I have a step attenuator inline and once I use about 20db it goes away pretty much.
So I am torn between removing the bypass mod and putting back to factory default or I may build a Loran C notch as described on Bjarne Mjelde website/blog.
As for software I have not really had much use with SDR# so am still learning it but even when I used the RSP2 I always turned to Simon Browns SDR console v3...for me its a winner all the way and its not even officially released yet !
The HF+ is certainly a very nice receiver and for the price it certainly packs a punch I have no regrets buying it
But if like me you will be using a active antenna and happen to be near a Loran C transmitter just maybe think twice before the bypass mode.  With a passive antenna I doubt it would be a problem.  If the Loran C was not such a messy transmission I doubt it would be a problem to the HF+ as it appears to handle strong signals exceptionally well for example the signal from radio 4 on 198khz end stops the s-meter on SDR console v3 put I don't get any interference from it.
Cheers
Mark
Southern Scotland


Alan G4ZFQ
 

Billy,

With software radios it is the software that matters.
The radios have no adjustments, for a blind person the ability to control the software is crucial.
The HF+ works with SDR sharp, SDR-Radio and HDSDR.
I am not sure about the first two but HDSDR has a lot of keyboard shortcuts to control it.
But, sorry, that is about all I know.

I should add that there are expensive table-top models with similar software controlled by knobs, but again, that is about all I know.

Alan

HI Mark, as there are a few of us thinking of purchasing the HF +, but are not too sure.