Re: An interesting noise blanker

by **Ivan** Thu Jun 09, 2022 2:08 pm

Andrew wrote: if one is plagued by switchiing PSUs, inverters and similar stuff, that NB may be a nice weapon

Hi Andrew,
if there is much QRM, it would be better to multiply the power line frequency by 6 instead of 2, as the QRM can come from all three powergrid phases. The frequency of blanking pulses would be 300 Hz in EU and 360 Hz in the US. A 4046 and a divider by 6 would perform the job.

here's another interesting RX antenna
http://www.crosscountrywireless.net/cardioid_loop_antenna.htm

This antenna could probably be made switchable to both modes by adding a switch or a relay across the 110 ohm resistor. Such antennas are good for ARDF on HF or for locating of QRM sources. First the rough azimuth to the TX is established by finding a maximum using the cardioid pattern. Then the exact azimuth is found by finding a (sharp) minimum using the "eight" pattern.

VBR from Ivan

by Andrew Thu Jun 09, 2022 9:09 am

sm0vpo wrote:
Ok Andrew.
I understand that a NB cannot tell the difference, and I also believe the best method is to remove the noise rather than muting the audio when the noise pulses are present.

Hi Harry !

Well, yes that's the idea behind that NB circuit, notice that it isn't just about "line noise" but also about noise which is radiated by some devices/lines, so if one is plagued by switchiing PSUs, inverters and similar stuff, that NB may be a nice weapon

I will do some work on antennas soon, but now I have to build my workshop/office/computer room. My new office/radio shack is 10 square metres and it was only yesterday that a gang of lifter removed 9 packing boxes of book and three 2m high bookshelves; a total of 350 books.

When I have done this I will have a shack at the antenna/garden side of the house. At the moment the shack is in a 5.5 square meter room, with not enough room to swing a cat, and the antenna feeder is 50m of RG-58 laid outside beside the house. Loss must be about 8dB and there is a lot of pickup.

Hey, sounds like you'll have a lot of "fun" Very Happy

as for the cable, if that's for RX only, a cheap run of RG6 (the one used for sat/tv) will serve you better than the RG-58 and probably pick up less noise

I have also got 18 m of decent double-screened, low-loss cable, and that is long enough to connect my radio to the antenna at the bottom of the garden. I am hoping that will really improve the noise levels and losses. I reckon the cable loss will be reduced to less than 1.5dB, at worst.

When the shack is at the back, I can have more than one cable, so I will have the opportunity to have seperate receiving and transmitting antennas, and if QRM is still a problem then the newly seeded/renovated lawn will become the home to a LOG antenna.

As for the coax, having two runs may be a good thing since it will allow to separate the feeders for RX and TX antennas, my suggestion is to add to the combo one or two CAT-5 cables, those will allow you to carry out whatever additional power/control line you may need (e.g. to control relays or a remote ATU or a remote varactor tuned preamplifier ... and so on) also, having separate CAT-5 to carry such stuff, you may add to the outside end of (one or both) coax a remote antenna switch controlled over coax like the one described here https://www.hayseed.net/~jpk5lad/K5LAD%20Memories/Vols%2031-35/Memories--Vol33.htm and you'll still have the CAT-5 lines to allow you to power preamplifiers and whatever else Very Happy

What else... oh yes, as for the LoG, willing to avoid issues when mowing the lawn, a trick is to pick some length of (relatively thin) garden hose, in such a case the LoG antenna wire will pass inside the hose, the latter will then be tied to ground and sealed at both ends (leaving a bit of the antenna wire out to connect the balun) to prevent water/mist from entering the hose, at that point you won't have issues mowing the lawn Very Happy

oh, and since we're at antennas, here's another interesting RX antenna

http://www.crosscountrywireless.net/cardioid_loop_antenna.htm

https://groups.io/g/CrossCountryWireless/topic/how_to_make_a_cardioid_loop/78194527?p=

the above has a nice cardioid pattern and works from LW/MW up to around 8MHz so it may be another weapon when seeking for signals Very Happy

by sm0vpo Wed Jun 08, 2022 10:25 pm

Ok Andrew.
I understand that a NB cannot tell the difference, and I also believe the best method is to remove the noise rather than muting the audio when the noise pulses are present.

I will do some work on antennas soon, but now I have to build my workshop/office/computer room. My new office/radio shack is 10 square metres and it was only yesterday that a gang of lifter removed 9 packing boxes of book and three 2m high bookshelves; a total of 350 books.

When I have done this I will have a shack at the antenna/garden side of the house. At the moment the shack is in a 5.5 square meter room, with not enough room to swing a cat, and the antenna feeder is 50m of RG-58 laid outside beside the house. Loss must be about 8dB and there is a lot of pickup.

The room is the second bedroom and it was Maj-Lis's library / gyest room. But nearly all the books were in Swedish and we have never had any guests in the two years we have been living here. So the little 5.5 sq.m room will become the new guest room with bunk-beds. I figure that any guest that comes to visit me wants to spend time with me, and not admiring the posh room. As long as it is comfortable.

I have also got 18 m of decent double-screened, low-loss cable, and that is long enough to connect my radio to the antenna at the bottom of the garden. I am hoping that will really improve the noise levels and losses. I reckon the cable loss will be reduced to less than 1.5dB, at worst.

When the shack is at the back, I can have more than one cable, so I will have the opportunity to have seperate receiving and transmitting antennas, and if QRM is still a problem then the newly seeded/renovated lawn will become the home to a LOG antenna.

As usual it is ~~work~~ [play] in progress.

BR Harry - sm0vpo (my third post on this forum).

by Andrew Mon Jun 06, 2022 10:29 pm

Well, Harry, a noise filter/blanker is the last resort imHo, since all of them can't really tell signal from noise; but if you can't setup a noise "killing" dedicated rx antenna like the Loop on Ground I suggested you time ago, then a noise reduction circuit may be useful

by sm0vpo Mon Jun 06, 2022 10:19 pm

Hi Andrew,
Thank you for sharing the link. I thought it was really interesting.

I have never used a noise-blanker, other than the preset on my new IC-7300. But here in Märsta there is QRM blanketing 1.8MHz, although 3.5MHz seems to be a lot better, only S7 of noise.

So if the QRM is really heavy, then it must often be in a state of permanent blanking? I have read the blurb, but I shall read it again when I have more time.

BR Harry - ~~SM0VPO~~ sm0vpo (new user, this is my second post)

by Andrew Wed Jun 01, 2022 2:26 pm

just stumbled upon this noise blanking circuit

http://www.ka7oei.com/syn_blank.html

and it seems quite interesting, also since it takes a somewhat different approach from the one found in regular NB circuits, plus it can be used "in cascade" with the receiver internal NB

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