1. Airspy
  2. Теми

AirSpy HF+ Dual Port Sensitivity Mod. Was: Airspy HF+ Discovery

 

On Mon, Dec 23, 2024 at 12:24 PM, Siegfried Jackstien wrote:

for good sensitivity on vlf and lf (and also better on mediumwave and 160m) i increased the input couplig cap in my hf+

see pictures ... (yes same antenna used and same gain settings)

That's a substantial increase. I had heard of this mod before but never screen captures of the before and after.
 
I'm tempted to try. What's the value of the cap?
 
73 de Vince, VA3VF
 

Very interesting results, Sigi.  Have you tried that modification on a 'newer' HF+ Discovery?  The images seem to suggest one of the older "pre-Discovery" HF+ models.  The presence of two SMA antenna ports looks like an older HF+ Dual-Port as opposed to the 'newer' single-port HF+ Discovery. 

The increase in gain down at the frequencies below 160 kHz is impressive.  Did you notice any indications of overload and/or increase in intermodulation signals?  The two images with the SDR tuned to 77.5 kHz seemed to indicate that there was not really any adverse impact on the noise floor, whereas the signals were night-and-day different.  The before-and-after images at 23.4 kHz were more difficult to compare the noise floor in that the signal strength scale changed, but again, the signals were night-and-day different.

More details about the capacitor value and any adverse indications like overload and intermod would be appreciated.  Great job, and thanks for sharing.  Merry Christmas, good DXing, and 73.

Ken -- WBØOCV

From: airspy@groups.io <airspy@groups.io> on behalf of DXer via groups.io <hfdxmonitor@...>
Sent: Monday, December 23, 2024 1:31 PM
To: airspy@groups.io <airspy@groups.io>
Subject: [airspy] AirSpy HF+ Dual Port Sensitivity Mod. Was: Airspy HF+ Discovery
 
On Mon, Dec 23, 2024 at 12:24 PM, Siegfried Jackstien wrote:

for good sensitivity on vlf and lf (and also better on mediumwave and 160m) i increased the input couplig cap in my hf+

see pictures ... (yes same antenna used and same gain settings)

That's a substantial increase. I had heard of this mod before but never screen captures of the before and after.
 
I'm tempted to try. What's the value of the cap?
 
73 de Vince, VA3VF

--

Ken, WBØOCV East Falmouth, MA USA
41.5997N, 70.5614W  FN41ro
 

0.01 to 0.1 uF as bigger you go as lower is the pass frequency

even 0.22 or 0.33 can be used without problems if you do not find a 0.1 uF in your junk box

i found no problems ... gain can be set to 0 or to -24 or -30 (only signal level changes but not the snr) ...tested on a non amplified passive wire loop with about 28m circumference and a 1:9 transformer

also connected to my 168m loop i see no problems

dg9bfc sigi


Am 23.12.2024 um 22:31 schrieb DXer via groups.io:

On Mon, Dec 23, 2024 at 12:24 PM, Siegfried Jackstien wrote:

for good sensitivity on vlf and lf (and also better on mediumwave and 160m) i increased the input couplig cap in my hf+

see pictures ... (yes same antenna used and same gain settings)

That's a substantial increase. I had heard of this mod before but never screen captures of the before and after.
 
I'm tempted to try. What's the value of the cap?
 
73 de Vince, VA3VF
 

no overload problems found ... I started with 0.01uF and already that made a big difference .... but now use an even bigger one with 0.1uF ... even bigger one does not hurt

i also tested 0.22 and 0.33 but that did not help any further to increase snr

what you receive and if you receive any "false" signals also depends a lot where you set the lo qrg and what bw setting you use ...

yes its the "older" dualport hf+ where the input cap just had a few pifs and sensitivity was very low at 160m and mediumwave and almost unusable on longwave and below (vlf area) ...

for testing you can just add the cap with two short jumper wires and test what value fits your needs (i guess that also depends a bit what antenna you connect) .... the input cap and the input "resistance" (impedance of the receiver) forms an RC highpass filter ... so no wonder if the input cap is small the sensitivitiy drops as lower you go in frequency

no i do not own a single port hf+ (i got that dualport as a donation (THANK YOU!!!) ... but found its performance to be very low on mediumwave and longwave and have read that you can modify it with bridging that cap ... to still have a dc block i then tried different values until i found it does not make it any better with increasing it further up ... closed the case and be done with it :-)

greetz sigi dg9bfc

Am 23.12.2024 um 23:03 schrieb Ken Sejkora via groups.io:

Very interesting results, Sigi.  Have you tried that modification on a 'newer' HF+ Discovery?  The images seem to suggest one of the older "pre-Discovery" HF+ models.  The presence of two SMA antenna ports looks like an older HF+ Dual-Port as opposed to the 'newer' single-port HF+ Discovery. 

The increase in gain down at the frequencies below 160 kHz is impressive.  Did you notice any indications of overload and/or increase in intermodulation signals?  The two images with the SDR tuned to 77.5 kHz seemed to indicate that there was not really any adverse impact on the noise floor, whereas the signals were night-and-day different.  The before-and-after images at 23.4 kHz were more difficult to compare the noise floor in that the signal strength scale changed, but again, the signals were night-and-day different.

More details about the capacitor value and any adverse indications like overload and intermod would be appreciated.  Great job, and thanks for sharing.  Merry Christmas, good DXing, and 73.

Ken -- WBØOCV

From: airspy@groups.io <airspy@groups.io> on behalf of DXer via groups.io <hfdxmonitor@...>
Sent: Monday, December 23, 2024 1:31 PM
To: airspy@groups.io <airspy@groups.io>
Subject: [airspy] AirSpy HF+ Dual Port Sensitivity Mod. Was: Airspy HF+ Discovery
 
On Mon, Dec 23, 2024 at 12:24 PM, Siegfried Jackstien wrote:

for good sensitivity on vlf and lf (and also better on mediumwave and 160m) i increased the input couplig cap in my hf+

see pictures ... (yes same antenna used and same gain settings)

That's a substantial increase. I had heard of this mod before but never screen captures of the before and after.
 
I'm tempted to try. What's the value of the cap?
 
73 de Vince, VA3VF

--

Ken, WBØOCV East Falmouth, MA USA
41.5997N, 70.5614W  FN41ro
 

On Mon, Dec 23, 2024 at 06:40 PM, Siegfried Jackstien wrote:

0.01 to 0.1 uF as bigger you go as lower is the pass frequency

even 0.22 or 0.33 can be used without problems if you do not find a 0.1 uF in your junk box

i found no problems ... gain can be set to 0 or to -24 or -30 (only signal level changes but not the snr) ...tested on a non amplified passive wire loop with about 28m circumference and a 1:9 transformer

also connected to my 168m loop i see no problems

dg9bfc sigi

Thank you very much, Sigi!
 
I'll try your non-amplified passive wire loop as well.
 
73 de Vince, VA3VF
 

its just half of a normal k9ay loop (one instead of two crossed loops) ... a ground stake .. a 1:9 (handwound) and a 560 ohms to ground on the reverse side

no relays, no control cables, no preamp ... just simle as that (if you can live with "half of the world only") ...

otherwise you need a few dpdt relays and two loops crossed (classical k9ay antenna) ... on shortwave my preamp in the rig is enough ... signals are a tiny bit lower as on the tx antenna but with a lot better snr

have fun

dg9bfc sigi

ps ... no preamp, no relays .. nothing that can fail or burn up if your tx antenna is close :-) and you can simply hang it down near a tree

Am 24.12.2024 um 01:44 schrieb DXer via groups.io:

On Mon, Dec 23, 2024 at 06:40 PM, Siegfried Jackstien wrote:

0.01 to 0.1 uF as bigger you go as lower is the pass frequency

even 0.22 or 0.33 can be used without problems if you do not find a 0.1 uF in your junk box

i found no problems ... gain can be set to 0 or to -24 or -30 (only signal level changes but not the snr) ...tested on a non amplified passive wire loop with about 28m circumference and a 1:9 transformer

also connected to my 168m loop i see no problems

dg9bfc sigi

Thank you very much, Sigi!
 
I'll try your non-amplified passive wire loop as well.
 
73 de Vince, VA3VF
 

On Mon, Dec 23, 2024 at 10:28 PM, Siegfried Jackstien wrote:
its just half of a normal k9ay loop (one instead of two crossed loops) ... a ground stake .. a 1:9 (handwound) and a 560 ohms to ground on the reverse side
Ahh...OK. I thought it was even simpler than that, similar to the one PA2OHH uses for QRSS reception.  :^)
 
I use a W2PM Mini Diamond Receiving Flag, my favorite RX only antenna. Easy to build, no active components and ground independent. The last two "features" practically mandatory for me, I'm tired of dealing with then in my very small suburban backyard. If curious about it, check the following link:
 
 
Not for VLF and LF though, as performance drops substantially around 1000kHz.
 
Thanks again and Seasons Greetings.
 
Vince, VA3VF
 

hmm ... looks like the k9ay is half of that loop (earth acts as a "mirror") but your loop is way smaller in size (lower sensitivity but usable up to 30 megs)

i guess the sensitivity on lf and vlf drops very low with such a small loop PLUS the transformer may not be big enough for those low frequencies

merry xmas to all

dg9bfc sigi

Am 24.12.2024 um 13:33 schrieb DXer via groups.io:

On Mon, Dec 23, 2024 at 10:28 PM, Siegfried Jackstien wrote:
its just half of a normal k9ay loop (one instead of two crossed loops) ... a ground stake .. a 1:9 (handwound) and a 560 ohms to ground on the reverse side
Ahh...OK. I thought it was even simpler than that, similar to the one PA2OHH uses for QRSS reception.  :^)
 
I use a W2PM Mini Diamond Receiving Flag, my favorite RX only antenna. Easy to build, no active components and ground independent. The last two "features" practically mandatory for me, I'm tired of dealing with then in my very small suburban backyard. If curious about it, check the following link:
 
 
Not for VLF and LF though, as performance drops substantially around 1000kHz.
 
Thanks again and Seasons Greetings.
 
Vince, VA3VF
 

its done in a minute or two (and reversible also) ...

for testing out the cap value you can solder two short jumper wires with alligator clips and test the sensitivity increase on the vlf and elf end and then fit a cap inside

lots of room to even use a non smd cap (picture shows a 0.01uF ... but i now use an even bigger one ... smaller in size but bigger in value)

dg9bfc sigi

Am 24.12.2024 um 13:50 schrieb DXer via groups.io:

Hi again Sigi,
 
On second thought, I'll wait a little longer before modifying the HF+ Dual Port.
 
I just received a Behringer UMC202HD external USB soundcard to try on VLF. This is the current recommendation from the guys on the VLF list.
 
73 de Vince, VA3VF
 

Airspy_hfplus_modding.jpg

 

On Thu, Dec 26, 2024 at 08:48 AM, Siegfried Jackstien wrote:

its done in a minute or two (and reversible also) ...

for testing out the cap value you can solder two short jumper wires with alligator clips and test the sensitivity increase on the vlf and elf end and then fit a cap inside

lots of room to even use a non smd cap (picture shows a 0.01uF ... but i now use an even bigger one ... smaller in size but bigger in value)

Hi again Sigi,
 
I'm only seeing your message here now. As I replied directly, VLF and LF are new interests. I also have a Discovery. The Dual Port is mostly for FM DXing. I don't know if I have an earlier production of the Dual Port, never checked. On second thought, it may be an earlier production, the one that needed a reset before upgrading the firmware for the first time.
 
73 de Vince, VA3VF

1 - 10 з 10