THE LISTENING POST.
- Thread starter BillC
- Start date
Hi Geoff, Bill would be able to clarify the issue a bit better, but my understanding is that it's only one or two stations that are overloading the reciever front end. My guesses would be 1260 and 756 as likely culprits. So rather than a band reject notch something a little less drastic and just a tunable notch for a specific frequency.
I found a tuneable one made by Chris Scott and associates, but seems to be no longer made. I'm thinking that you could knock up something suitable using a few parts from an old AM transistor radio. Salvaging the ferrite rod and tuning capacitor for a parallel resonant circuit could be a good start.
I found a tuneable one made by Chris Scott and associates, but seems to be no longer made. I'm thinking that you could knock up something suitable using a few parts from an old AM transistor radio. Salvaging the ferrite rod and tuning capacitor for a parallel resonant circuit could be a good start.
Just for fun, here is a quick example of a pi type reject notch filter calculated for 3SR 1260 kHz. Simulated sweep from 500 kHz to 1700 kHz using QUCS. QUCS is a free download from https://qucsstudio.de/
Here is a band stop filter that kills the whole AM band. I have ordered PCB's and parts to make a couple for testing.
MW Band Notch Filter
MW Band Notch Filter This device is specifically designed for radio enthusiasts and operators who experience interference from strong local Medium Wave (MW) broadcast stations. ...
www.rx-888.com
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A Very Nice deep notch Ray, I never much cared for horses either.
Hi Geoff and Ray, The AM band stop filter could be very handy. Some recent study on my part has suggested that overload on lower bands may upset the noise level performance in the higher frequency ranges especially with a wide range device e.g. SDR. I might build an equalization filter too. There is plenty of chance for experimentation. Cheers.Here is a band stop filter that kills the whole AM band. I have ordered PCB's and parts to make a couple for testing.
View attachment 3450
MW Band Notch Filter
MW Band Notch Filter This device is specifically designed for radio enthusiasts and operators who experience interference from strong local Medium Wave (MW) broadcast stations. ...www.rx-888.com
Here is a WORK LOG for the LISTENING POST to date. Just in case any of you radio enthusiasts might be looking to install a remote SDR. The following could help with planning etc. This log basically deals with site preparation,construction and reinstatement. The WORK LOG - dig pit for tower base,back fill and ram dirt. assemble tower,mount fittings and halyards. raise tower. dig four foot hole for post, place post and back fill and ram by hand. dig six four foot deep holes for hut poles, place poles back fill and ram by hand. construct the hut frame and clad with CGI. fit solar panel mounting pole. mount data and GPS antennas. fit two earth stakes,dig fifty meters of trench, lay coax cables back fill and roll dirt, source and cut six poles for hut, source and cut the listening post 3.5 mt, source and cut four 11.5 mt poles for the loop, source and cut four 3.5 mt stumps for loop pole mountings, dig holes and place four stumps for the loop poles, fit up and raise four 11.5 mt loop poles, bolt poles to stumps, lay out fit up and raise the loop wire, connect coax. Now to enable the loop to be constructed on the site, as follows, dismantle 90 mt of fence, Now to repair, dig eleven fence post holes, place eleven posts, back fill and ram by hand, fit up four end assemblies, hang and fit two gates, reconnect the fence parts and strain up around 56 wires. I suppose most will not bother to read this all, but the reading is a lot easier than the doing!
VK3EB
Active member
Looking good Bill.
We can try the flydog on the loop and see if it overloads, the kiwi's have a RF unity buffer amp, could that be a problem, needs checking.
If the broadcast band signals are and ongoing problem we need a notch from say 500k to 1meg it seems to be the stations in the bottom half of the MW band.
We can try the flydog on the loop and see if it overloads, the kiwi's have a RF unity buffer amp, could that be a problem, needs checking.
If the broadcast band signals are and ongoing problem we need a notch from say 500k to 1meg it seems to be the stations in the bottom half of the MW band.
Good idea, I think the band stop filter from the web-888 website could be modified to cover the lower AM band, I have pcb's and parts ordered, so when they arrive, I'll give you and Bill a couple to play with.
Lots of people like listening to the AM broadcast band ( except for the horse station 1260 !! ) and it would be a shame to block the whole of the band, and even in some cases decrease the sensitivity on the 160M band.
Bill's big loop is an amazing antenna, we just need a receiver configuration to take full advantage of it's incredible performance.
Lots of people like listening to the AM broadcast band ( except for the horse station 1260 !! ) and it would be a shame to block the whole of the band, and even in some cases decrease the sensitivity on the 160M band.
Bill's big loop is an amazing antenna, we just need a receiver configuration to take full advantage of it's incredible performance.
VK3EB
Active member
Mr Kiwi also has a MW filter, but again made with lots of attenuation, we only want a little bit.
Main culprits are 594, 756, 675, 1260 is strong via ground wave but remains steady, skywave not an issue like other stations.
kiwisdr.nz
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Main culprits are 594, 756, 675, 1260 is strong via ground wave but remains steady, skywave not an issue like other stations.
SDR MW Filter
Designed by John Futter ZL2J, this bandstop filter attenuates signals in the MW band 500kHz to 1.5MHz for locations that have very high levels from a nearby broadcast station. It is bandstop, not high pass so the VLF band is unaffected. The circuit is covered in clear heatshrink for physical...
kiwisdr.nz
VK3EB
Active member
More ideas to reduce overload on SDR's, from a well known SDR owner.
ka7oei.blogspot.com
Revisiting the "Limited Attenuation High Pass" filter - again.
In several previous posts (See: " A Limited Attenuation High Pass Filter " and " Revisiting the Limited Attenuation High Pass Filter " I d...
ka7oei.blogspot.com
VK3EB
Active member
Given the wide band nature of the sampling front end , I reckon you are right Ray. The overloading at the lower frequency end upsets the noise performance higher up. We shall experiment with Equalization Filters.A bit of light reading....
I wonder how much of the noise is actually coming from intermod products in the AM band. My guess would be it's a significant contributor.
Here is an article by L.B. Cebic (SK 2008) that was presented at Atlanticon '99. The HOHPL Antennas, or, Horizontally Orientated, Horizontally Polarized Large Wire Loop Antennas. Probably listed as- HO-HO- HOHPL's
He prepared a large number of Antenna Modelling article that were originally listed on his website, now at:- https://www.antenna2.net/cebik/
It is a series of .gif files within the article.
He prepared a large number of Antenna Modelling article that were originally listed on his website, now at:- https://www.antenna2.net/cebik/
It is a series of .gif files within the article.
I have been working on a Band Stop filter today, juggled a few component values and tested this evening, the idea seems to be working. Check the images, marker 1 at abt. 470khz and marker 2 at abt. 1750 khz . I think the filter took around 4 hrs to build. I will try a live test on Friday morning around 9AM.
Looks good Bill, the printed circuit boards for the Band Stop Filter arrived today, but I'm still waiting on the components to populate the board
it will be interesting to see what difference these filters make to the intermod noise.
Getting low loss at 160 M is nice.
it will be interesting to see what difference these filters make to the intermod noise.
Getting low loss at 160 M is nice.
Cheers Ray I decided to connect the filter this evening so as to be able to test it in the strong signal environment that night time presents. As we observed the mid band attenuation of the broadcast signals looks good. The Horse Station was 14.1 millivolts ( - 24 dbm), now with the filter in line the signal has dropped to 0.286 millivolts ( - 58 dbm) also 3RN has dropped to 0.64 millivots ( - 51 dbm) . I reckon that the band stop filter idea will work and we will try your filters when they are ready. Cheers !!