I own a shortwave receiver (bought from Radio Shack) I built back in the late 70s from a kit, a Science Fair "Globe Patrol". It still works(!) but not well: for an antenna I'm using a @22ft piece of 18 gauge wire strung up on my room's walls, and tuning is very erratic/unpredictable and just placing my hand near the metal face plate causes major static issues. I am very sure this is occurring because it requires an external ground & living in an apartment I am not able to install a 4ft copper rod into the soil outside my window as I did 40+ years ago, so I cannot provide it with that.
Is there any way to convert this radio to an internal ground system, like so many portable SW radios use? I've uploaded a scan of the radio's schematic to aid with this. FYI: electronics-wise, I never progressed past building simple gear like this, so hopefully I have the skills to undertake such a conversion (if it's even possible).
BTW, I am aware the electrolytic capacitors may have aged sufficiently to cause their own problems, but I want to figure out the grounding issue first.
I appreciate any advice with this! 🙂
Is there any way to convert this radio to an internal ground system, like so many portable SW radios use? I've uploaded a scan of the radio's schematic to aid with this. FYI: electronics-wise, I never progressed past building simple gear like this, so hopefully I have the skills to undertake such a conversion (if it's even possible).
BTW, I am aware the electrolytic capacitors may have aged sufficiently to cause their own problems, but I want to figure out the grounding issue first.
I appreciate any advice with this! 🙂
What's happening with the static is your body is acting like the other end a capacitively coupled dipole antenna, thus increasing the radio's RF sensitivity as you adjust the coupling. You get background static because there is more resulting RF signal strength.
If not a dipole as Marcel suggested, you could also try grounding the radio to a cold water pipe, or to AC power ground, say, through the screw that holds an AC outlet cover on.
Whatever you do, the radio antenna/ground system you set up will be sensitive to frequency and to arrival direction of radio signals you are trying to pick up. Therefore moving the antenna around and or adjusting its length may help with pick up of particular stations.
If not a dipole as Marcel suggested, you could also try grounding the radio to a cold water pipe, or to AC power ground, say, through the screw that holds an AC outlet cover on.
Whatever you do, the radio antenna/ground system you set up will be sensitive to frequency and to arrival direction of radio signals you are trying to pick up. Therefore moving the antenna around and or adjusting its length may help with pick up of particular stations.
From the circuit diagram this is a regenerative (i.e. not a heterodyne type with an IF) receiver. It should be adjusted close to self-oscillation with VR1, where sensitivity is at maximum. When you overadjust it, it will function as a RF transmitter. No wonder this type is not produced any more (perhaps against to FCC rules, too).
There is a tremendous amount of RF noise in most buildings. Switching power supplies, motors and many other sources. A large loop antenna can reject much of it. Try winding about 10 turns of wire around a couple if crossed wooden supports and connect to the ground and antenna terminals. Two yardsticks or something similar could be used. Such antennas do have sharp directivity nulls and can be used to reject inteferrers. You will just have to experiment with tuning and positioning to get best performance. Once tuned to a station such antennas can perform surprisingly well. This radio is simple conceptually, but take quite a bit of finesse to bring in stations. They can be very sensitive and high performance. They were meant to encourage expirimentation. Search loop antennas to get more ideas. Have fun!
Thanks for the explanation. The AC power ground method sounds interesting (if a bit ominous! 🤔), though the screws here are painted - have to dig up some sandpaper first......
RF noise: yep! Recently I walked around with my Sony ICF-P36 portable switched to the AM band, and placed it near various electrical devices. WOW. LED bulbs were among the worst, along with phone chargers. But the worst offenders by far were a 42" flatscreen TV and its accompanying Polk Audio soundbar - especially the latter, which generated eerie noises like something heard in a sci-fi movie. On the other hand, my Pioneer A/V receiver was pretty much silent, despite all its processing chips and large power supply (no surprise here though, since such a device needs to be electrically quiet).
That antenna sounds easy to assemble (and that's a good thing since I'm on a budget) - thanks for the suggestion.
Markw4: I appreciate the links.
BTW, if anyone wants to see this radio, you can do so via the following excellent website: https://www.radioshackcatalogs.com/flipbook/1979_radioshack_catalog.html
It's located on page 137. FYI: to go there directly, enter that number into the black rectangle at the bottom of the page. Use scroll wheel to enlarge page.
BTW, if anyone wants to see this radio, you can do so via the following excellent website: https://www.radioshackcatalogs.com/flipbook/1979_radioshack_catalog.html
It's located on page 137. FYI: to go there directly, enter that number into the black rectangle at the bottom of the page. Use scroll wheel to enlarge page.
Shouldn't be painted on the back side. The screws are commonly used for grounding ground adapter plugs such as the ones at: https://www.amazon.com/ELEGRP-Groun...1&sprefix=ground+adapter,aps,173&sr=8-15&th=1
The little silver tab with a hole in it is for that same screw. Its used to ground the adapter.
Markw4: I forgot about those adapters - thanks (full disclosure: I'm a bit paranoid about 120V-related systems: the only 120V kits I've made are an on/off touch switch from Heathkit; a sound activated "color organ", another RS kit; and a 9V DC power supply kit made in an 8th grade electronics course that used a large ceramic resistor to drop the 120 volts to 9 volts i.e. no transformer used! Yes, that resistor became hot quickly & I only used that supply once).
The AC line ground the cover screw is connected to is in turn connected to a ground rod near the main breaker panel at each building. There is also another ground rod at the distribution transformer secondary (e.g. the small-ish transformers you see mounted on local telephone poles). Just don't stick things that don't belong there into AC wall outlet slots where the power is.
I had one of those as a kid. It is a regenerative receiver. It will never perform as well as a superheterodyne.
You can probably get a shortwave radio very cheaply since there isn't much on shortwaves nowadays. I have a DX-390 that I fire up on occasion when I am feeling nostalgic.
Ed
You can probably get a shortwave radio very cheaply since there isn't much on shortwaves nowadays. I have a DX-390 that I fire up on occasion when I am feeling nostalgic.
Ed
I didn't mean to imply I get sweaty palms just inserting the plug of a device into an AC outlet - I realize that screw, being exposed, IMO couldn't pose a shock hazard.
Fun facts: I have received a 120V shock twice, definitely not pleasant & obviously lived to tell about it, but for me the worst shock I received was via the ignition coil on a '73 Corolla. I briefly touched the rubber-covered plug cap on the cable leading to the distributor cap & didn't realize I was standing in a small puddle of water in our garage. Doing so literally & immediately knocked my arm backwards with no conscious effort of my own, not to mention the pain was nearly as bad as the 120V incidents. My dumb teenager brain didn't think the ignition system of such a small engine could do such a thing!
I bought a little Kaito WRX911 a couple years ago. Works pretty well but unfortunately you're right, as far as what it can pick up there's not much to listen to. I was prepared for this while reading reviews before buying it, but still have hope something is still out there that's interesting.
You can try it on a battery supply, to rule out mains induced noise.
HF means about 1.5 to 2 meters long vertical wire...may work, if outside the window.
An old whip antenna from a surplus source may work, common in military and police use.
Search for 'Yagi array'.
And yes, receivers are cheap, a diary sized unit, cheap Chinese item, is less than US $3 here in India.
HF means about 1.5 to 2 meters long vertical wire...may work, if outside the window.
An old whip antenna from a surplus source may work, common in military and police use.
Search for 'Yagi array'.
And yes, receivers are cheap, a diary sized unit, cheap Chinese item, is less than US $3 here in India.
Shortwave radios with external antennas can sometimes be useful for troubleshooting electronics. Described using one for that myself here in the forum. IIRC sometime later someone else told me Jim Williams talked about doing more or less the same thing at one of the old Silicon Valley engineering get-togethers.
Some kind of handy signal tracer for conducted EMI/RFI, is what I used it for.
Some kind of handy signal tracer for conducted EMI/RFI, is what I used it for.
This receiver operates on four "C" cells, so fortunately mains noise isn't a problem.
Unfortunately, I live in an apartment & am pretty sure the management would frown on a wire hanging outside the window.😕 BTW when I bought the kit I also purchased a shortwave antenna system, also from Radio Shack (see it on page 166, underneath the Realistic DX-160 receiver).
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