Messages

31

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

32

General Radio Discussion / Re: Scoop: Congress moves to preserve AM radio in cars

« on: May 21, 2023, 1835 UTC »

I assume you are talking about the wording in Sec 2: 7 (a) and (b).  I don’t read it that way.

To me, the way the whole bill is written implies they really want digital AM.  If the car radio only had conventional AM, it would not be compliant.  It would have to be a hybrid receiver.  Sec 2: 14 (b) 3 clearly shows they want digital.

I could see this as a bone thrown to the automobile manufacturers as it might ease their worries about vehicle generated RFI.  The RFI would still be there, but the end consumer would not hear it.  All he would notice is poor range on AM.

The exclusion against an all digital AM station receiver is weird.  Maybe that is a concession to all of the analog AM stations out there, that they are being included.

33

General Radio Discussion / Re: Scoop: Congress moves to preserve AM radio in cars

« on: May 21, 2023, 1353 UTC »

It’s worth noting that the proposed bill specifically calls for digital audio AM receivers.

34

SDR - Software Defined Radio / RX-888

« on: May 15, 2023, 1330 UTC »

I don’t know how recent this is.  Phil Karn KA9Q is developing a multi channel program to work with the RX-888 receiver.  He calls it KA9Q-Radio.  I don’t see a date on the sdrutah page.  The youtube link looks to be a month old.
I don’t know how recent this is.  Phil Karn KA9Q is developing a multi channel program to work with the RX-888 receiver.  He calls it KA9Q-Radio.  I don’t see a date on the sdrutah page.  The youtube link looks to be a month old.

http://www.sdrutah.org/info/using_ka9q_radio_with_the_rx888.html

https://github.com/ka9q/ka9q-radio

This Youtube video has Phil talking about it.
https://youtu.be/7nhBFSGby2o


edit:

KA9Q-Radio is actually designed to work with multiple radios, like the RTL-SDR and the AirSpy.  The neat thing about it is the ability to simultaneously decode multiple channels.  A radio that could capture the entire HF spectrum, like the RX-888 might have, would allow the ability to capture all HF at once.  In the video Phil shows how he has been capturing every 2M, 440, and 220 repeater in his location all at once, using 3 Raspberry Pi computers, and saving to disk.  He said he had 2 years of data, occupying about 2 TB.

Phil says his code is relatively stable now and he is looking for other programmers to develop better end user interfaces.

35

Equipment / Wellbrook Antennas closing

« on: March 24, 2023, 1526 UTC »

Wellbrook antennas is closing at the end of April.  The owner is retiring.

https://www.wellbrook.uk.com/loopantennas/

36

VHF/UHF Logs, including satellites and radiosondes / Re: UHF mil air

« on: February 21, 2023, 1510 UTC »

On this page, that I've linked to in several places in this very thread, is a box where you can enter your zip and see logs from within whatever rx range chosen;
http://www.milradiocomms.com/mil_freq_database.html

I’d advise caution on this link.  It worked for me a long time ago when I tried it, but now it delivers strange behavior and browser security alerts.  I think it is compromised.

37

For Sale / Wanted / Barter / Re: WTB/WTT For Halicrafters SP-600 Reciever

« on: January 23, 2023, 1337 UTC »

I think you are looking for a Hammarlund SP-600, not a Hallicrafters.

Hallicrafters made their own version of the SP600, called the R-274 or SX-73.  While it was supposed to be functionally the same, it looked much different.  They are somewhat rare and I have only seen a handful over 50 years in the hobby.

https://www.radioblvd.com/hallicrafters_r274_receiver.htm

38

Longwave Loggings / Re: WA1ZMS/4 486 AM 1212 UTC 25 DEC 2022

« on: December 27, 2022, 1413 UTC »

Heard S6 at 0140Z on 25 Dec 2022.  I was using a Wellbrook loop and a KiwiSDR, located in Northern VA.  It wasn’t audible on a end fed wire due to local EMI.

39

General Radio Discussion / Re: Garage Door Opener Damaged by HF RF?

« on: December 11, 2022, 1559 UTC »

Testing this should be easy enough.  Look at your garage door receiver to see what the operating frequency is.  Use a SDR like a RTL or a RSP and examine the spectrum near that frequency, looking for strong signals. 

If you don’t know the door opener frequency, look at the entire spectrum from 300 to 400 MHz.  Most garage door openers seem to operate in this range.

If the problem is there all the time,  an interfering signal would be there all the time, like a LMR repeater.  It would be pretty strong to override your car remote.

Around here we have Government trunk radio systems in the 380 MHz frequency range.

40

General Radio Discussion / Re: Garage Door Opener Damaged by HF RF?

« on: December 11, 2022, 1410 UTC »

We had a number of locals suddenly have problems with their garage door openers.  The problem turned out to be a new trunked radio installation at a nearby government base.  The local hams were able to verify that the new system was up and running by using SDR receivers.  The local press picked up the story.

As I remember, the garage door openers that were impacted were using frequencies in the 300 MHz band as secondary users.  The government was primary, but agreed to delay going operational with the new system for a short time to give homeowners a chance to modify their door openers.  Amazon sells new receivers to retrofit older openers.

Considering how this problem suddenly impacted everyone, RFI seems a likely cause.

https://www.insidenova.com/headlines/top-secret-government-center-admits-interference-with-fauquier-garage-door-openers/article_b09dd948-0116-11ea-b4d6-db45151e2c1c.html

https://www.creativedoor.com/blog/troubleshooting-garage-opener-remote-range-and-interference-issues

41

Equipment / Re: Can a LoG be too big?

« on: December 02, 2022, 1220 UTC »

Isn’t that the truth?  Lord help you if they find a way into your attic.  My Lab has gotten quite good at chasing them from the bird feeders while barking “Get off my lawn”.  She caught one once and it had the audacity to bite her before she dispatched it.  Since then it has changed from a game to serious Lab business.

42

Equipment / Re: Can a LoG be too big?

« on: November 30, 2022, 1232 UTC »

….but for those buying, an 1000' spool of flooded direct bury bulk RG-6 is under $100 shipped on eBay. That builds several typical LoGs or one quite large LoG.

Good point, but I will stick with the THHN wire for this season because I still think the squirrels will still be a
problem.  Repairing a wire break will be much easier.

43

Equipment / Re: Can a LoG be too big?

« on: November 29, 2022, 1209 UTC »

Do not put too much thought into impedance transformation IMO. An 1:1 should suffice if needing additional isolation for common mode, though admittedly I ran my LoG for many years without any balun or transformer. 1:1, 4:1, or whatever else tried when constructed did not affect it much. FWIW, there were just a few relatively useless ferrites on the feedline near the feedpoint.

I think that a significant part of a successful LoG is suppressing common mode pickup on the feedline.  I would either use ferrite cores (type 77 or 75 if your interest is LF) or a CM filter (KD9SV and DXEngineering sell them).  Place a filter at the antenna feedpoint and at the receiver.  Burying the feedline helps a lot and may even negate the need for the common mode filter.

44

Equipment / Re: Can a LoG be too big?

« on: November 29, 2022, 1134 UTC »

   The only way to make one last (here anyway) would be to use large gauge wire, which is cost prohibitive.

I’m going to try another loop this year….a bit smaller, maybe 500 ft.  This time I will use #14 THHN electrical wire (I used cheap CCA CAT5 last time).  I’m hopping this will be more rodent resistant.  I’ve got no idea how sunlight tolerant THHN is, but I will know soon enough.

THHN has jumped in price - a few years ago a 500 ft spool was about $50.  Today it is closer to $80.

45

Equipment / Re: Can a LoG be too big?

« on: November 28, 2022, 1249 UTC »

I ran a 1000 ft LoG one winter season.  It worked well (my interest was in LF at the time).  I didn’t pay much attention to directionality effects.  It worked on other bands too.   I used a 9:1 balun.

When I went to pull it up in the Spring I found it was in pieces.  Squirrels had chewed on it during the winter.  I would recommend you take a continuity measurement of the loop after you install it.  Later, if performance seems off you can recheck it to see if squirrels have had their way with your antenna.  This is a lot quicker than walking the length of the antenna.

Considering that BoG antennas are shorter than their elevated counterparts, a 1000 ft on the ground is like a much larger elevated loop.