Bandpass Filter 1420MHz - Bias-Tee or not?

[Anthony]

I purchased these 1420 MHz bandpass filters to help the Saw H1+ LNA with interference signals. I've searched the Internet but can't find if these need Bias T for power. Not even on the Tindie website.

So, I'm assuming no power (Bias-Tee) is necessary?

https://www.tindie.com/products/gpio/1420-mhz-bandpass-filter-hydrogen-line-radio-astro/

[Marcus D. Leech]

Nope.  in *general* RF filters are completely passive.  IN fact, they may well NOT LIKE IT if there's power present on their ports, and you may need to come up with
  a "sneak around" for DC with these.    The filtering on the SawBird H1+ is quite good, so the only reason to have another filter right up at the receiver is if you
  have a longish cable run, and you are possibly getting some leakage through the coax of modest-to-high RF fields--a filter right in front of the receiver may be
  useful there.

--
--
You received this message because you are subscribed to the Google
Groups "Society of Amateur Radio Astronomers" group.
To post to this group, send email to sara...@googlegroups.com
To unsubscribe from this group, send email to
sara-list-...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/sara-list?hl=en
---
You received this message because you are subscribed to the Google Groups "Society of Amateur Radio Astronomers" group.
To unsubscribe from this group and stop receiving emails from it, send an email to sara-list+...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/sara-list/CAKU65TyC643m4%2BXywufhAdQMQfOFmyO-QxxP8ExuAy0Eyegr7g%40mail.gmail.com.

[Anthony]

My cable run is 25 feet, but I'm switching tonight to the low resistance 3-meter cable, not sure if this S-LMR240 coax with 50 ohms is great. I'm using a DC block, downstream the Saw H1+, then plugging the bandpass filter after the DC block, then the coax downstream to the receiver. I'm tempted to use another LNA to boost the signal, but remember what you said, unless I'm having long cable runs of 100' then that would most likely prove to boast interference or flooding?

https://www.amazon.com/dp/B07P12XW3J?psc=1&ref=ppx_yo2_dt_b_product_details.   

If I'm not mistaken, there were other lower low-loss signal cables, I need to find that SARA post. I've switched out my Blog V3 RTL-SDR in place for the AirSpy Mini and won't use Bias-Tee for the bandpass filter. 

Do you use Sensitive, Linear, or Free for the Airspy Mini settings, along with the IF plugin? Seems like the Free configuration has a higher RF Gain or SNR than the other selections. 

To view this discussion on the web visit https://groups.google.com/d/msgid/sara-list/733ce4a8-ccd5-285c-f210-d675a77124e1%40gmail.com.

[Anthony]

By the way, the Sawbird H1 is using external power, so the DC block is needed. 

On Sat, Sep 18, 2021 at 5:36 PM Marcus D. Leech <patchv...@gmail.com> wrote:

To view this discussion on the web visit https://groups.google.com/d/msgid/sara-list/733ce4a8-ccd5-285c-f210-d675a77124e1%40gmail.com.

[Marcus D. Leech]

On 2021-09-18 5:55 p.m., Anthony wrote:

By the way, the Sawbird H1 is using external power, so the DC block is needed.

Yeah so if it's powered externally (via USB connector for example), I'd put a DC-block on either end of your coax--because I'm paranoid about these things :)


Antenna-->SAWBIRD--DC-BLOCK----->COAX------>DC-BLOCK---->FILTER--->AIRSPY

WOuld be what I would do.

To view this discussion on the web visit https://groups.google.com/d/msgid/sara-list/CAKU65TwSHwrFdLKuMWQSbPGaxVtX8LRRGb6YvO4XYLu7-%2BN%2B7A%40mail.gmail.com.

[Anthony]

Ok, fortunately, I have another DC block. The other night the Hydrogen neutral signal peaked, during transit and faded as the galactic plane moved away from my Zenith, but I'm unsure because the signal range was 1420.4 - 1420.6, I need to validate tonight. 

RTL-SDR or Airspy Mini, Marcus? 

To view this discussion on the web visit https://groups.google.com/d/msgid/sara-list/cc1eba78-3c29-8fa9-95b0-0995034653c7%40gmail.com.

[Marcus D. Leech]

On 2021-09-18 6:10 p.m., Anthony wrote:

Ok, fortunately, I have another DC block. The other night the Hydrogen neutral signal peaked, during transit and faded as the galactic plane moved away from my Zenith, but I'm unsure because the signal range was 1420.4 - 1420.6, I need to validate tonight. 

RTL-SDR or Airspy Mini, Marcus?

Either will work, to be honest. The total range of galactic hydrogen is about +/- 1MHz.  I just happened to use AirSpy in my setup.

To view this discussion on the web visit https://groups.google.com/d/msgid/sara-list/CAKU65TybVTca3ahusi4NRy-sU73a4apRX81MZYCHqaG8tHYy0A%40mail.gmail.com.

[bsn...@gmail.com]

I have a Mini_Circuits VBF-1445 bandpass filter just at the SDR input.  The bias-t injector is "downstream" (toward the antenna) of the filter.

The filter seems to eliminate a bit of low-level RFI from the LEDs lights above my work area, from the wireless LAN switches, and other assorted electronic "stuff" in the shack.

I  have a 72 feet run of Belden 9913 coax that runs over the 220v line to our well and there are assorted FM radio stations towers within  2 miles.

Marcus, thanks for the Tractor Supply tip...I need to rebuild my 3-D corner reflector with something other that aluminum sheets ---it's like a mini-sail on windy days. :-)

....bill....

[Anthony]

Results of H1 emission observation, 1.53-minute timelapse video, and one screenshot attached. 

https://youtu.be/xe5K1Q9TV3Q

To view this discussion on the web visit https://groups.google.com/d/msgid/sara-list/08bbb9b3-0376-f30d-6ae2-2156831422a3%40gmail.com.