Re: MW Images In LW Band

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ridgescan

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Re: MW Images In LW Band

Just wanted to make an observation to all who are participating in WA8ZTZ's thread "Ham Tranceiver As LW RX" regarding my receivers here. First, I want to thank the guys over there for the low-pass filter suggestions. I will look for those.
But here's my point-it's very perplexing to me that my Icoms R75 and R71a, one a double-conversion and the other a triple conversion and both are legendary-each get strong MW images every 10kHz in LW. But here's the rub: my single-stage Realistic DX-160 gets NO images at all in LW! I wonder why that is. And this is with RF gain all-out and ant. trim full-on. LW is actually cleaner on that older, less complex rig. I wonder if it has something to do with the LW band in the DX160 not being as staunchly aligned to the tee as the other two? Or not being digital.
EDIT: I forgot to add something maybe important; the DX 160 runs via an Alpha Delta antenna switch to the Wellbrook loop.
 
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majoco

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Yes, Ridgy, and you will see from the snippet of the schematic attached that it again adheres to the 'maximum selectivity before any amplification or frequency changing" theory. Directly from the antenna connection on the left via the RF gain control and a couple of clipping diodes, the signal goes to one of five tuned transformers - tuned by the "Main tuning" control - what you have is an effective tuned preselector right at the front of the receiver keeping the BC band rubbish out while you listen to the LF band. Very good design in a 'domestic' receiver. Should be a very hot receiver with the FET RF amplifier tuned both sides.
 

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ridgescan

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Thanks Marty:) that's really something there and I appreciate the education. Hey the SX-88 has the similar "preselector" within it and wouldn't that be a killer LW rig as you've said before!
Also I should add that the DX-160 has fantastic selectivity sans filters in MW. I can snuggle right up next to the fat mamas there and pick out some weak ones hiding under their skirts:D.
 

SDRPlayer

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I have never heard a more apt description of dxing!! Awesome!
 

WA8ZTZ

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These MW "images" you speak of may not be true images but rather various mixing products.
Judging from the description of your QTH relative to KFSO (in the other thread) and based on a quick search, it looks like the KFSO signal at your QTH is somewhere near 100 mV/m. Plus there are at least another half dozen or so stations that cover your QTH with at least a 50 mV/m or greater signal. Yikes ! You live in the RF equivalent of Death Valley. It is amazing that you do as well as you do given what you are up against. A mind boggling array of potential internal and external mixing combinations. However, hopefully, all is not lost. The solution includes filtering and preselection. Additionally, you want to make sure that all your antenna and grounding connections are clean and tight, no corrosion.
 

ridgescan

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These MW "images" you speak of may not be true images but rather various mixing products.
Judging from the description of your QTH relative to KFSO (in the other thread) and based on a quick search, it looks like the KFSO signal at your QTH is somewhere near 100 mV/m. Plus there are at least another half dozen or so stations that cover your QTH with at least a 50 mV/m or greater signal. Yikes ! You live in the RF equivalent of Death Valley. It is amazing that you do as well as you do given what you are up against. A mind boggling array of potential internal and external mixing combinations. However, hopefully, all is not lost. The solution includes filtering and preselection. Additionally, you want to make sure that all your antenna and grounding connections are clean and tight, no corrosion.
Plus I have Sutro Tower about 1.7 miles from me. Along with gobs of agencies, cellphone stuff, pagers, and TV, KFOG FM is up there and drives right through my FM traps. Hence I am a stickler for reliable connections and grounding like you said.
 

dlwtrunked

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Plus I have Sutro Tower about 1.7 miles from me. Along with gobs of agencies, cellphone stuff, pagers, and TV, KFOG FM is up there and drives right through my FM traps. Hence I am a stickler for reliable connections and grounding like you said.

Get a better FM trap or use two. I use two from Mini-circuits and they almost even kill the station only 0.8 miles away. https://www.minicircuits.com/pdfs/ZBSF-95+.pdf but they are about $100 each.
 

Boombox

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I used to get a few MW images in the LW on my DX-160, but use of a tuned loop on LW got rid of all of them. I also agree, the DX-160 is an excellent MW DX machine. Fun to use, also.
 

dlwtrunked

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Thanks for the advice and links-I am using two Radio Shack FM traps (remember those?) and I should invest in better ones.

I have used the Radio Shack ones. In some cases they are fine but in measurements, they are not as good and are especially poor at the low end of the FM band (88-90 MHz). But they are better than nothing. I also use the ones available on eBay for portable use--they are cheaper and not as good as the Mini-Circuits but worthwhile.
https://www.amazon.com/Broadcast-FM...d=1521115720&sr=8-1&keywords=sdr+fm+broadcast
Of course you will likely needed coax adapters for the SMA connector to whatever.
 

ka3jjz

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A little OT here, as the topic clearly states MW as the source, however....

If memory serves me correctly, the 88-90 Mhz range is reserved for lower power FM broadcasters; however if you're really close to the tower, I can see where that might cause issues in some cases.

PAR electronics is one place to check for FM traps (as well as MW filters); they are a bit expensive but well worth it...now let's get back on topic...Mike
 

ridgescan

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I thank all of you for the help and links! BTW KFOG operates on 104.5megs and is 7100 watts. Good good info guys-just gotta get old Frank to try and peel open his wallet:D
 

WA8ZTZ

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Another idea to perhaps enhance your LW listening experience... Given your challenging RF environment, a low pass filter by itself may not be enough. If this proves to be the case, Tee the input of a high pass filter (500 kc and above) into the line before or after the LPF ( experiment here to see which may be best). Terminate the output of the HPF with a 50 ohm load (51 ohm or 2 100 ohm in parallel carbon resistors). Be sure to use carbon resistors as they are non-inductive. You will have an L network that passes the desired low frequencies on to the RX while shunting and absorbing the undesired higher frequencies.
 

ridgescan

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Another idea to perhaps enhance your LW listening experience... Given your challenging RF environment, a low pass filter by itself may not be enough. If this proves to be the case, Tee the input of a high pass filter (500 kc and above) into the line before or after the LPF ( experiment here to see which may be best). Terminate the output of the HPF with a 50 ohm load (51 ohm or 2 100 ohm in parallel carbon resistors). Be sure to use carbon resistors as they are non-inductive. You will have an L network that passes the desired low frequencies on to the RX while shunting and absorbing the undesired higher frequencies.
Thanks for this info. I emailed PAR for pricing on both filters and am waiting for the replies.
 

ridgescan

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WA8ZTZ

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These two
SWL Filters | PAR Electronics | Filters for the commercial 2 way market, MATV, FM broadcast, laboratory, marine industry, amateur radio, scanner and short wave listening enthusiasts
He emailed me back and said they're $69.95 each plus $14.00 shipping-I need to ask him if that's $14 per filter or to ship both. Why-you know of any maybe cheaper yet very good?

The LPF (low pass filter) passband is 0 to 500 so that would pass all the LW frequencies and stop AM broadcast band and higher frequencies. This filter would go in line with the antenna coax lead-in and should be placed as close as possible to the RX.

The other filter is a HPF (high pass filter). Its specs say it will pass frequencies above 1700 and therefore attenuate all frequencies below 1700. If you were planning on using this as the HPF in the L network as described in my earlier post #15, it would have no affect on the AM broadcast band. It would only shunt and absorb freqs higher than 1700. For this particular dual filter L network application you would need a HPF that passes everything above 500 so as to absorb the unwanted AM broadcast signals.

Did a quick search and couldn't find a readily available off the shelf HPF that would work in the application described above.. You may have to build your own. Or, you could contact PAR and see if they could build one. In fact, you may want to explain your situation to them and see what else they may have or recommend. No sense in reinventing the wheel.

Hopefully my rather long winded reply didn't confuse you. Any questions don't be afraid to ask.
 

ridgescan

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The LPF (low pass filter) passband is 0 to 500 so that would pass all the LW frequencies and stop AM broadcast band and higher frequencies. This filter would go in line with the antenna coax lead-in and should be placed as close as possible to the RX.

The other filter is a HPF (high pass filter). Its specs say it will pass frequencies above 1700 and therefore attenuate all frequencies below 1700. If you were planning on using this as the HPF in the L network as described in my earlier post #15, it would have no affect on the AM broadcast band. It would only shunt and absorb freqs higher than 1700. For this particular dual filter L network application you would need a HPF that passes everything above 500 so as to absorb the unwanted AM broadcast signals.

Did a quick search and couldn't find a readily available off the shelf HPF that would work in the application described above.. You may have to build your own. Or, you could contact PAR and see if they could build one. In fact, you may want to explain your situation to them and see what else they may have or recommend. No sense in reinventing the wheel.

Hopefully my rather long winded reply didn't confuse you. Any questions don't be afraid to ask.
No Sir, not confused at all. Your way of direct explanation is why and the more I read your stuff I can see you've a lot of knowledge. I appreciate it!
 
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