Messages

16

SDR - Software Defined Radio / SDR front end filtering and preamps

« on: September 07, 2023, 1240 UTC »

http://ka7oei.blogspot.com/2023/09/

KA7OEI’s conclusions:


“….The best HF weak-signal performance for the RX-888 (Mk2) will occur with the receiver configured for "High" gain mode, 0 dB attenuation and a gain setting of about 20dB.  Having said this, you should always to the "antenna versus no antenna" test:  If you see more than 6-10dB increase in the noise level at the quietest frequency, you probably have too much gain.  Conversely, if you don't see/hear a difference, you probably need more gain - taking care in doing so.

For best HF performance of this - or any other wideband, direct-sampling HF SDR (RX-888, KiwiSDR, Red Pitaya, etc.) additional filtering is suggested - particularly the "shelving" filter described above.

In situations where the noise floor is very low (e.g. a nice, receive quiet location) many direct-sampling SDRs (RX-888, KiwiSDR, Red Pitaya) will likely need additional gain to "hear" the weaker signals - particularly on the higher HF bands.  While some of these receivers offer onboard gain adjustment, the use of external high-performance amplification (along with filtering and careful adjustment of the devices' gain adjustments) will give improved absolute sensitivity while helping to preserve large-signal handling capability.

Because the RX-888 is a computer-connected device, there will be ingress of undesired signals from the computer and the '888's built-in circuitry.  The use of external amplification - along with appropriate decoupling (e.g. common-mode chokes on the USB cable and connecting coaxial cables) can minimize the appearance of these signals…….”

17

Equipment / Re: Grounding receiver ??

« on: September 01, 2023, 1358 UTC »

If I can add on to what Chris and others have already said…

Much of the confusion over grounding is rooted in not understanding why you are doing this.  There are probably a half dozen different goals someone might be pursuing in “grounding”, and what you do to accomplish them may be in conflict with each other.  Examples include (but are not limited to):

* Electrical Safety
* Lightning Protection
* EMI Control
* Hum prevention
* Antenna counterpoise needs

I see people make mistakes grounding their station all the time when they mix these up.

For instance, in the US, the National Electric Code (NEC) has a section that states a grounding conductor is not required to be larger than #6 gauge.  However, this is in a section that deals with electrical safety.  #6 was chosen because that was enough to ensure that safety devices like circuit breakers would function normally.  Larger wire was unnecessary for that purpose.  Lightning protection, however, is covered in another document.  #6 would be inadequate for that purpose; you would want a larger conductor to ensure most of the surge current went down that path rather than alternate grounding paths.

Ufer grounds are another example.  In the US they are allowed for electrical safety grounding.  I wouldn’t want to use that as a means for lightning protection grounding though.  I would be worried that the heat generated from the lightning surge would cause entrapped moisture in the concrete to vaporize and explode the concrete.

Adding to the confusion are frequency dependent effects.  An adequate grounding design for 60 hz probably has problems at 6 MHz.

When designing a grounding system for my station, I would start with an NEC compliant implementation for electrical safety.  Then I would address changes for lightning protection.  I would follow that with any measures necessary for EMI control, ensuring that I didn't compromise any steps taken for the first two.

18

General Radio Discussion / HF Traders

« on: August 13, 2023, 1453 UTC »

This epub contains a number of news about applications for FCC STAs.  Most of the issues have an article of some sort about HFT stations.  It is free, but you do have to provide your email address.

https://www.experimentalradio.news/

19

General Radio Discussion / Long Wave STA

« on: August 13, 2023, 1433 UTC »

From Experimental Radio News, issue 8:

(https://www.experimentalradio.news/experimental-radio-news-8/)

Longwave for remote sensing

Lunasonde was issued Special Temporary Authorization WV9XBO for experiments at 119-121 kHz, as it develops an Earth-sensing constellation to detect ground resources.

“Lunasonde’s ability to look 15,000 times deeper than current satellites and sensors is the next frontier in resource exploration," the company said. “Our small satellite can locate groundwater, mineral deposits, and other geological resources up to two kilometers underground. Our data is collected in three minutes and provides a true 3D map of the earth's subsurface."

For the low-frequency STA, “The proposed testing is necessary to increase the technology readiness level of the Lunasonde LF transceiver. A 100-foot structure located in Tucson, AZ will transmit in the requested frequency band.

“During a test mission, one uncrewed high-altitude balloon will carry one LF receiver system approximately 60,000-100,000 feet above ground level over the transmission structure. Transmitted signals that reflect from the Earth’s surface would be received by the free-floating balloon receiver system. ...

“The system is equipped with a redundant cut-down device, a radar reflector, and an ADS-B transponder… The balloon is returned to the ground either when it reaches maximum altitude (approximately 100,000-130,000 ft) or when the cutdown is commanded, at which point a parachute is used to safely return the payload to the ground. In either scenario, Lunasonde will retrieve the balloon and equipment.”

‘No expectations’ for future approval

“Lunasonde, Inc. shall have no expectations that future requests for operational use of this transceiver from low earth orbit using the 119-121 kHz band will be approved, and Lunasonde, Inc. should ensure that any future operational use of this equipment be conducted in appropriately allocated frequency bands,” the FCC told the company.

20

Pirate Radio History / Re: The 1620 WJDI Story

« on: August 07, 2023, 0942 UTC »

I saw Dave at the Berryville, Virginia Hamfest yesterday.  He had a large booth space outside, selling electronic parts.  I haven’t seen him at a hamfest in a long time.  He seemed to be doing well and I was able to chat with him for a few minutes.

21

General Radio Discussion / Re: Fair Radio Sales is Closing

« on: August 05, 2023, 1018 UTC »

I’ve been expecting this (with sadness) for a while.  I don’t know of any other dealer of military surplus electronics left.

It’s hard to appreciate the sheer magnitude of surplus electronics that hit the market at the end of WW2.  Even some 25 years after WW2 (when I got started in ham radio), you could still buy things like ARC5 receivers still sealed in their factory packages.  Heathkit built their company on military surplus components.  There were scores of local surplus stores throughout the country…I can remember several in the Wash DC area where I grew up.  The legends about Radio Row in NYC are unbelievable.

Today, the government would rather destroy their surplus than sell it.  While the reason given is often about embedded security devices, manufacturers like Motorola would rather sell the public new equipment than compete with their own offerings via the surplus market.  There is a case to be made that the commercial aviation manufacturing industry after WW1 was depressed due to the number of surplus aircraft the government sold.  Maybe that is the reason so many aircraft after WW2 ended up going to the scrappers rather than the public.

You can see early catalogs from Heathkit, Fair Radio, G&G electronics, etc here:

https://worldradiohistory.com/Electronics_Catalogs.htm

22

Equipment / Re: Solar Panel RFI 18 Jul 2023

« on: July 26, 2023, 1041 UTC »

It was an article by K1KP in the April 2016 issue of QST.  The issue was all of the panels were connected in series and due to the geometry of the wiring you ended up with a large loop of wire which was more efficient in radiating noise.  The recommendation was to double back the wire (to eliminate the open surface area of a loop).  The downside is the additional length of wire and it’s IR drop.  You probably ought to look at the article; the explanation is clearer than mine.

It’s the same article as the RSGB file link in Sigint’s posting earlier.

23

Equipment / Re: Solar Panel RFI 18 Jul 2023

« on: July 26, 2023, 1023 UTC »

I seem to remember something from a QST article years ago that talked about the impact of how the wiring was run from the panels making a difference.  In one case the wires were twisted together; and in another the two panel wires were separated and ran on different edges of the panel because this made it easier to connect up multiple panels.  The twisted wires radiated less noise as I remember.

24

Equipment / Re: Solar Panel RFI 18 Jul 2023

« on: July 24, 2023, 1150 UTC »

Some advice:

http://ka7oei.blogspot.com/2020/08/it-is-possible-to-have-rf-quiet-home-pv.html

25

The RF Workbench / Re: All Electronics going out of business

« on: June 27, 2023, 1113 UTC »

I chatted on the phone with one of the employees.  She said that it has been very busy with a lot of in store and on line sales since the closing was announced.

The reason for the closing was simply that the owners wanted to retire.  We’ve seen that before with Universal Radio, EZNEC, and others.  I can think of several other dealers/vendors that are probably approaching the same situation. 

26

SDR - Software Defined Radio / Re: KiwiSDR future/replacement?

« on: June 22, 2023, 1515 UTC »

Yeah, I should really stop.

Please don’t!

Your efforts are greatly appreciated by everyone I know.

I own literally dozens of receivers yet my Kiwi is the one I use the most.  It works well and the integrated decoders are exceptionally convenient.  For all it does and how well it works, I still marvel at the tiny footprint it has and how little it actually cost.

Most hams and SWLs go through their life enjoying the hobby, but contributing little.  Not so for you.  You’ve made a huge impact.

27

The RF Workbench / All Electronics going out of business

« on: June 19, 2023, 1238 UTC »

All Electronics, a vendor of electronic parts, is closing in August.  They were a source of some hard to find electronic parts (like old school high voltage mica transmitting capacitors).

www.allelectronics.com

28

The RF Workbench / Ferrites and Inductors for EMI Control

« on: June 01, 2023, 1732 UTC »

This is a good basic article on choosing ferrites and inductors for EM noise suppression.  It discusses choices, best practices, and why your filters may be ineffective.

https://digital.incompliancemag.com/issue/june-2023/inductors-and-ferrites-for-use-in-emc/

29

Equipment / State of HF transceiver art

« on: May 25, 2023, 1120 UTC »

This is from the 2023 CTU, and discusses the performance of current HF transceiver offerings.  Most of the discussion is on receiver performance.

Note that it says 60,000 Icom IC7300 radios have been sold.  This is surely the most popular HF radio ever.  I have heard anecdotal stories of SWL’s buying them just to use as a receiver.

https://www.contestuniversity.com/wp-content/uploads/2023/05/Transceiver-Performance-Selection-of-a-Radio-2023.pdf

30

SDR - Software Defined Radio / SDRPlay SDR Receiver problem

« on: May 23, 2023, 1127 UTC »

This article identifies the possibility of undesired signals when using SDRPlay receivers.

While the article focuses on SDRPlay, the problem might exist on other brands.  If this turns out to be a problem for you, the fix is to use an outboard filter.

http://ka7oei.blogspot.com/2023/05/


One possible source of low cost bandpass filters is here:

http://www.qrp-labs.com/bpfkit.html


and low pass filters here:

http://www.qrp-labs.com/lpfkit.html