Antenna noise?

Thread Starter

ApacheKid

Joined Jan 12, 2015
617
Like I mentioned in an earlier thread I'm playing around with setting up an antenna for my much under used Icom IC-R75 receiver.

Yesterday I setup a pretty poor basic antenna but this was purely a "what if" experiment, not intended to become a real antenna.

It is a horizontal wire about 33 ft. long, mounted about 7ft off the ground.

One end is directly attached to a metal hook screwed into a wooden structure (that encloses my chickens) the other is also attached to a metal hook screwed into the masonry wall near where my workshop/garage door is, that hook is electrically insulated (well galvanically) because it is screwed into a plastic wall plug.

That end of the wire has a tough multi stranded copper wire joined as part of the wire's crimp, for now it's just coming in through a gap on the garage door, of course the door and supporting frame is all steel and aluminum, a lot of metal.

The wire is stainless steel and I used aluminum "crimpable" sleeves to create the end loops of the wire.

Here are a few pics:

1642432018244.png

1642432049883.png

1642432078510.png

So this is a crude, poor "long wire" antenna I suppose, with the "feed" being a direct connection to one end.

The receiver has two antenna connectors available:

1642432478257.png

1642432400141.png

On the right, the red/black are Ant2 and the SO239 is Ant1, the one in operation is selectable from the front panel.

My antenna is connected to the red and there is nothing connected (yet) to the black.

I believe I have a DSP option installed (Can't recall because I bought this new in 2001 and have hardly ever used it).

OK, so having said all that and given you the details of the setup, here's the big observation, I can get some signals but there's a lot of noise. In particular there's a noisy "tone" that's fairly constant across a wide spectrum from like 5MHz up to around 25MHz where it begins to diminish.

That noisy tone is greatly reduced in LSB/USB mode, but very pronounced in AM mode.

What might that noise be? if its some local RF interference then that's pretty much the end of any DXing aspiration because I have no idea what it is, where it comes from or whether it can be reduced.

This was just a crude experiment, I have all sorts of insulators on order as well as coax and other stuff and fully intended to do a much better job, this was just to see what kind of stuff I experience with a very crude setup and the noise is a concern.


Thoughts?

PS: I don't have a simple portable transistor radio around just now, but I do seem to recall very decent reception when I did have one, can't recall if I ever tried that portable on AM though...
 
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nsaspook

Joined Aug 27, 2009
9,444
See if connecting an earth ground to the P.7 helps. RFI/EMI is a big problem in a world filled with digital electronic gadgets. A coax shielded input feed might also help. You might want to try a magnetic loop antenna because many times the localized near-field RFI/EMI sources are high impendence with less energy in the magnetic component of the noise signal.
https://swling.com/blog/2015/10/gue...guide-to-mitigating-urban-radio-interference/
https://swling.com/blog/2018/02/indoor-shortwave-antenna-options-to-pair-with-a-new-sdr/
 

MisterBill2

Joined Jan 23, 2018
11,580
Yes, first a good ground to the radio. Then, to see if the noise is coming from your place, while listening, switch off the circuit breakers one at a time to see if any have an effect. I recently experienced huge noise while attempting to track a power cable in a basement with a dozen LED bulbs. Noise much stronger that the tracer signal. Also, try it with a different antenna, a hunk of insulated wire on the ground.
Cheap switching power supplies have a reputation for huge amounts of noise production. Grow lights being an earlier worst case.
 

Thread Starter

ApacheKid

Joined Jan 12, 2015
617
See if connecting an earth ground to the P.7 helps. RFI/EMI is a big problem in a world filled with digital electronic gadgets. A coax shielded input feed might also help. You might want to try a magnetic loop antenna because many times the localized near-field RFI/EMI sources are high impendence with less energy in the magnetic component of the noise signal.
https://swling.com/blog/2015/10/gue...guide-to-mitigating-urban-radio-interference/
https://swling.com/blog/2018/02/indoor-shortwave-antenna-options-to-pair-with-a-new-sdr/
OK I will try that, I'll get that connected to the house electrical ground.

I did discover that once I get below approx 1.5 MHz, I get more reasonable behavior, many stations, the noise is hardly present and it behaves like a "normal" radio, but as we get to 2, 3MHz and upwards the stations become very scarce and the noise more pronounced.

Perhaps it is just very poor at these frequencies and the noise is nothing special...
 

Thread Starter

ApacheKid

Joined Jan 12, 2015
617
Attaching the wiring system ground to the black rear connector has no audible effect, either on a pure noise frequency or when I have a reasonably clear AM station on; at say 1.5 MHz or so.
 
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SamR

Joined Mar 19, 2019
4,122
Great radio! I use coax coming into the house to eliminate noise pickup from house AC, Switches, and all the muck on my bench. And an Unun.
ant.JPG.png
The Zap Trapper is Lightning Suppression. And coming into the house is an MFJ Window Pass-Thru For Coax With a GND stud connected to a driven 10' copperclad Ground rod by bare #10 copper wire. I also have an inside ground buss block connected to it for anything I want to ground directly instead of through the inside power wiring safety ground. Notice that all of the other coax entries are also lightning suppressed.
GND.png
I would also highly recommend the MFJ preamp and tuner. The Alinco is the Power supply for my ICOM XCVR just below the riser under the R75.r75.png
There is a Hi Voltage 3Ph feeder in front of the house so running the antenna perpendicular to the feeder helps a bit as does the MFJ.

Edit: Good thing I took that picture, just noticed my #10 ground rod connection was missing. Someone must have knocked it loose weedeating! It's back on now! Need to replace the spade with a ring connector and bolt it down with a hex nut instead of the wing nut! No lightning suppression without a ground. Plus it left my XCVR ungrounded as it uses a 2 wire connection from the Alinco power supply instead or having a 3 wire grounded house power cordset.
 
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Thread Starter

ApacheKid

Joined Jan 12, 2015
617
This is very useful info @SamR

I will likely get an ATU can only help I guess, in a few minutes I'm going outside to setup some simple insulators, easy enough to play with and see what happens.

The coax too is a simple idea I can, try I have a bunch of old coax sitting around so a simple experiment is pretty doable.

Thanks
 

Thread Starter

ApacheKid

Joined Jan 12, 2015
617
Something that confuses me about this receiver @SamR is that if I just set the frequency to say 15.0 MHz then press "SCAN" the displayed frequency immediately jumps to 1.0 MHz and it starts scanning from there, totally confusing me.
 

Thread Starter

ApacheKid

Joined Jan 12, 2015
617
Another that has always mystified me, if an ATU is a simple device (which they are) then why isn't it simply built into the receiver?
 

SamR

Joined Mar 19, 2019
4,122
Scanning is confusing on the R75 and even on my XCVR. You have to set up the scanning parameters using its menus. Start f, Stop f, rate, etc. You'll have to read the manual. I use Ham Radio Deluxe computer software with a serial connection to the R75 to scan with. It used to be free software, but he got bought out years ago and it's now a commercially paid product. But it is much easier to program and even generates waterfall visual representation of the scan and can easily be used to lock in on the spikes of broadcasts. It now cost $150(?), and I use it also with my XCVR but it is USB instead of Dshell. Very similar to what you use with a SDR dongle. There are also some online band opening reports and visuals of band performance online.
 

Thread Starter

ApacheKid

Joined Jan 12, 2015
617
Scanning is confusing on the R75 and even on my XCVR. You have to set up the scanning parameters using its menus. Start f, Stop f, rate, etc. You'll have to read the manual. I use Ham Radio Deluxe computer software with a serial connection to the R75 to scan with. It used to be free software, but he got bought out years ago and it's now a commercially paid product. But it is much easier to program and even generates waterfall visual representation of the scan and can easily be used to lock in on the spikes of broadcasts. It now cost $150(?), and I use it also with my XCVR but it is USB instead of Dshell. Very similar to what you use with a SDR dongle. There are also some online band opening reports and visuals of band performance online.
Ahh OK so there are parameters that govern this, I had no idea, I lost the manual some years ago, have hardly used the radio and today lazily speed-read the manual PDF.

THx
 

SamR

Joined Mar 19, 2019
4,122
Another that has always mystified me, if an ATU is a simple device (which they are) then why isn't it simply built into the receiver?
Most of the Ham Rigs and I think the RCV that replaced the R75 do have it built in now. My first tuner was a Heathkit model good for 2kW and bigger than a breadbox. Huge roller inductor and air capacitors. The R75 was a big step up in sensitivity and software defined filtering and audio refining from the older units. The new units are pretty much microprocessor/computer controlled.
 

SamR

Joined Mar 19, 2019
4,122
I don't know where my manual is but I do know where my PDF is! LOL Someone also published little cheat cards and booklets for them that may still be available. I had/have them also, especially for my XCVR and it's kept under it for quick access.
 

Thread Starter

ApacheKid

Joined Jan 12, 2015
617
Well I'm certainly using the receiver better than I was yesterday, still most AM signals are being found around 1.5MHz and below which is really MW and not SW, after that they are scarce or unrecognizable.

I'm a pretty good listener too, spent a lot of time in my teens with headphones on old radios seeking out faint signals.
 

SamR

Joined Mar 19, 2019
4,122
I used to enjoy listening to China Radio I think it was. Came on early in the morning as I was getting ready for work. Always enjoyed listening to the hilarious spin they would put on world news. Always good for a laugh and enjoyable way to start the day. Their response to BBC and VOA.
 

Thread Starter

ApacheKid

Joined Jan 12, 2015
617
I once got a true QSL card, I think it was from Singapore or Burma or some place like that if I recall, picked up the station one afternoon in the early 1970s (when I was a teen, I lived in Liverpool UK back then) and wrote down all the details and mailed off my "SINPO" rating of the station.

The radio was an old tube desktop radio, good quality, nice colored glass front with tuning dial that moved a pointer across the face, probably a 1960s model of some kind.

Back then my antenna was no better than what I setup yesterday but perhaps was a lot longer, running around the inside edge of our back yard wall.
 
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Thread Starter

ApacheKid

Joined Jan 12, 2015
617
I would isolate you antenna wire with insulators, such as shown in post #6.
It may not help, but it's good practice.
I just tried this, used some decent cable ties for now, I also ordered a bunch of ceramic egg insulators too.

I guess 33ft is also really not very long, now I do have rather a lot of space so might attempt a much longer one as my next experiment. But I'm very curious too about the height, the current thing is only 7ft above the ground.
 

Thread Starter

ApacheKid

Joined Jan 12, 2015
617
Well my coax arrived, 40 feet with presoldered PL259 at each end. This coax is/was intended to be routed along the interior wall of my workshop and connect up to the receiver which would be on a shelf.

For now, I've soldered an SO239 connector right to the antenna wire outside and cut off the simple temp wire I had been using, that's white wire you see in the first image in this thread, now you can see a SO239 soldered onto that white wire.

This has had zero effect on the noise which is audible from 2 MHz to around 20.5 MHz.

I'm gonna shut down this PC to see if this is the source...
 
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