Kracken RF Discovery Drive

[Stephen Arbogast]

Here is  an update....    https://www.crowdsupply.com/krakenrf/discovery-drive/updates/project-status-report-a-new-video-review-and-more-faqs

I asked  about  RFI  from  the  drive  motors and WiFi  and immediately got  a  response asking   "what frequency?"  So  I immediately  replied  the  Hydrogen  Line at 1420.405751768 MHz.  So far no reply  so  maybe  they  are  doing  some testing...    I hope.

I know there is some concern about this......

Stephen

[Alex P]

Its not so much the "Frequency" as its  "Amplitude" as the first LNA transistor is Unfiltered.

[Stephen Arbogast]

Alex,

I think  I remember  at some  time in the past  I was  reading   about  the  Kracken RF  Hydrogen Line  feed  and  I seem  to remember it  uses  two filters  one before  and  one  after  the LNA   but  my memory might be  wrong.

Still,  I am looking  forward to  the  response  from Kracken RF.

[b alex pettit jr]

Not Before : that would require an expensive integrated cavity filter.

I can't photo my antenna when in use as the autofocus motor momentarily  fills the screen with spikes even when the camera is 10-15 ft away

Alex

[b alex pettit jr]

[Stephen Arbogast]

I  am still  waiting  for  Kracken RF  to  reply  to my questions.    I am confident they will.  I have  not  ordered  the   discovery  drive  yet   because  of  some   concerns  expressed  here in SARA.  I am hopeful  the  discovery  drive is  a success.

On Thursday, March 26, 2026 at 5:28:46 PM UTC-6 b alex pettit jr wrote:

[Adrian]

"as the first LNA transistor is Unfiltered. "    That isn’t entirely accurate, because in most practical LNA designs the first stage active device, usually a FET rather than a bipolar transistor, is not actually exposed to the antenna without filtering. Its active control gate is almost always fed through a series coupling capacitor that, together with the antenna’s source impedance, forms a high‑pass filter path whose cutoff frequency increases as the capacitor value decreases. This naturally suppresses lower frequency signals while allowing the intended higher frequency components to reach the LNA but still subjecting the first stage to potential RFI from the higher frequencies passed by the input capacitor high pass characteristics.

[Andrew Thornett]

Hi Folks,

Can I ask how the amplification and filtering on Discovery feeds compares to the Nooelec design?

As I understand it (please correct me if I am wrong), the Nooelec works as follows:

LNA with sufficient amplification to compensate for losses on the SAW filter.

-->

SAW filter +/- 50 MHz centred at 1420 MHz.

-->

2^nd LNA providing amplification to compensate for losses on the coaxial cable to SDR.

Andy

Sent from Outlook for Android

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From: sara...@googlegroups.com <sara...@googlegroups.com> on behalf of Adrian <kjan...@gmail.com>
Sent: Saturday, March 28, 2026 4:00:32 AM
To: Society of Amateur Radio Astronomers <sara...@googlegroups.com>
Subject: [SARA] Re: Kracken RF Discovery Drive

 

"as the first LNA transistor is Unfiltered. "    That isn’t entirely accurate, because in most practical LNA designs the first stage active device, usually a FET rather than a bipolar transistor, is not actually exposed to the antenna without filtering. Its active control gate is almost always fed through a series coupling capacitor that, together with the antenna’s source impedance, forms a high‑pass filter path whose cutoff frequency increases as the capacitor value decreases. This naturally suppresses lower frequency signals while allowing the intended higher frequency components to reach the LNA but still subjecting the first stage to potential RFI from the higher frequencies passed by the input capacitor high pass characteristics.

On Thursday, March 26, 2026 at 4:07:28 PM UTC-7 Alex P wrote:

Its not so much the "Frequency" as its  "Amplitude" as the first LNA transistor is Unfiltered.

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[Adrian]

LNA (First low noise stage-critical) with sufficient amplification. (10-15 dB)

-->

SAW filter +/- 50 MHz centred at 1420 MHz.

-->

2^nd  (second stage-low noise not as critical) providing more amplification (another 15-20 dB) to compensate for losses on the SAW filter and therefore sufficient to compensate for losses on the coaxial cable to SDR.

https://www.everythingrf.com/rf-calculators/cascaded-noise-figure-gain-calculator

[Adrian]

In the late 1970s–early 1980s bipolar transistors faded out of serious use in first‑stage L‑band LNAs once low‑noise FET technologies—especially GaAs FETs and later pHEMTs—began outperforming BJTs in noise figure, input impedance behavior, and stability at microwave frequencies.

In RF contexts—like that in an LNA—the series RC is typically described by its function:

• Series coupling capacitor (if R is the source impedance, e.g., 50 Ω)
• "High‑pass input network"
• RC matching network (if part of an impedance‑transforming structure)

The name shifts depending on whether the goal is DC blocking, shaping the passband, or setting the input match.

[Stephen Arbogast]

Here is the  datasheet  for  the  IC  used in the  Kracken RF  Hydrogen  Line  feed  with performance  measurements so all can see.  Note  the  schematic is  given  for a  development board  available  from Qorvo.  I think it  would  easy to make  one's own  pcb...   add  rf connectors, bias T, and  a saw filter.

I am  still waiting  for a reply  from Kracken RF  about  my  question of RFI  from  the  Discovery Drive  due  to wifi,  motors,  esp32.....

[b alex pettit jr]

[Adrian]

Stephen

       If you are planning to make your own boards make sure to pay attention to this as it will make a significant difference

Adrian

[Stephen Arbogast]

I have no  plans  to make my own boards   but please explain?????

[Adrian]

Alex 

  In the QPL9547 spec sheet for the QORVO Evaluation Board - QPL9547EVB-01 note the important C1, 100 pF capacitor placement. This is for its design range of  0.1 ~ 6 GHz Ultra Low-Noise Amplifier.  This value works well since  the 3dB roll off with 100 pF is ~ 32 MHz needed to get down to that low 0.1 GHz broadband input design. For 1420 MHz though it would be much better to drop it down to ~22–47 pF to still keep the corner well below 1420 MHz at ~ 144 MHz  and still knock down HF/VHF crud without too much of an impedance mismatch to the MMIC transistor.

Adrian

[Stephen Arbogast]

Oh,   thanks!

[Adrian]

The use of PTFE/Teflon boards rather the more common FR4 which is a glass epoxy dielectric composition laminate, has significant influence on the circuit board design such as the width of traces to match the desired 50 ohm typical impedances. It influences other characteristics as well as overall active device function in the microwave bands.  Although for 1420 MHz going either way is not too great of an issue you just need to know which one you are planning to use or which circuit design you are planning to replicate to maximize things such as the noise levels etc. The PTFE board materials are usually called by the common names of a popular manufacturers such as Duroid  and Rodgers 

Adrian

[Marcus D. Leech]

On 2026-03-28 22:27, Adrian wrote:

The use of PTFE/Teflon boards rather the more common FR4 which is a glass epoxy dielectric composition laminate, has significant influence on the circuit board design such as the width of traces to match the desired 50 ohm typical impedances. It influences other characteristics as well as overall active device function in the microwave bands.  Although for 1420 MHz going either way is not too great of an issue you just need to know which one you are planning to use or which circuit design you are planning to replicate to maximize things such as the noise levels etc. The PTFE board materials are usually called by the common names of a popular manufacturers such as Duroid  and Rodgers 

Adrian

Indeed, dielectric loss on a PTFE substrate is generally lower--particularly if you go for thinner boards.  But at 1420MHz, you can get *close* using thinner
  FR4, and the input as close as damned possible to the gate input of the pHEMT.

The other thing I found with some PTFE substrates is that doing rework of any kind was next to impossible.  The traces liked to lift off at the slightest
  provocation.  I found this when trying to modify consumer LNBFs to take an external 27MHz clock.  Ruined 3 of them before I got one that "took".  Sigh.

To view this discussion visit https://groups.google.com/d/msgid/sara-list/bdd35964-43cb-443a-811f-063f0594ec1an%40googlegroups.com.

[Stephen Arbogast]

You  guys   are getting   me  stirred  up.  I have used  FR4  from JLCPCB for  all  my boards in the past.  I might  have to try  this PTFE/Teflon .  Don't  know  if  JLCPCB  supports this.

[Don Latham]

PTFE is noisy when flexed and will become easily charged when rubbed. Also cold flows under pressure. But has remarkable electrical. insulation properties. Just for fun, hook up a teflon cable to a guitar practice amp sometime and jiggle the cable.

 

------------
Don Latham
PO Box 404,
Frenchtown, MT, 59846
406-626-4304

 

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From: Marcus <patchv...@gmail.com>
To: sara-list <sara...@googlegroups.com>
Date: Saturday, 28 March 2026 8:47 PM MDT
Subject: Re: [SARA] Re: Kracken RF Discovery Drive

To view this discussion visit https://groups.google.com/d/msgid/sara-list/080e1328-14ef-4f9e-8f1d-17a3959ba365%40gmail.com.

[Stephen Arbogast]

Kracken RF   has not  replied to my question  about  RFI from  discovery  drive  even  after I replied  to their  request  of what frequency   I  was asking  about.  Does this mean  that  yes  there is some  observed   rfi  from wifi, esp32 and  drive motors? 

[A. C.]

I guess if all else fails you can put your dead Duroid 21cm LNA on an electric guitar, use it as a pickup and play Lynyrd Skynyrd's Free Bird on it.  LOL.

Adrian

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Adrian

"My God, it's full of stars!"
 Dave Bowman

[Stephen Arbogast]

Well.....   I  do  play   guitar..  mostly Blues  on my   acoustic...   I  built   this  Fender Champ....5c1