Homebrew Antenna for DIY Receiver

[OscarKilo]

Hi all,

Recently I have built a K8TND regen receiver seen here: K8TND Regenerative Receiver - QRPGuys

It may be a little more esoteric than most shortwave receivers, but that is part of the fun of it for me. Unfortunately, I have yet to pick up any transmissions on it. All I've got is a random wire antenna made from 100' of 14ga stranded wire. I can't get it very high off the ground, so I'm wondering if an indoor antenna might work better in my situation. Does anyone have any recommendations for a better antenna? Would such a long antenna produce an impedance mismatch between it and the receiver?

I'm located in Vancouver, Canada, north of Seattle. It is probably not the best location for monitoring shortwave, and apparently conditions aren't too good for propagation right now. I'm hoping a better antenna might improve my chances of picking something up. I'm sure the receiver is functioning as it should, but I use the antenna with an AM crystal radio and SDR receiver with no trouble.

Thanks for any suggestions!

 

[WA8ZTZ]

First of all, congratulations on building your own receiver.
My guess is that you may have to play with the windings on that T1 toroid. It can be a bit tricky to get
a regen set to function properly. It would be nice if you can access a signal generator to provide a
known steady signal source.

 

[OscarKilo]

First of all, congratulations on building your own receiver.
My guess is that you may have to play with the windings on that T1 toroid. It can be a bit tricky to get
a regen set to function properly. It would be nice if you can access a signal generator to provide a
known steady signal source.

Thanks WA8ZTZ! I have tried moving the windings around on the toroid, and the receiver seems to oscillate with the regen turned up. A signal generator would come in handy. If I disconnect the antenna, the hiss in the speaker gets quieter, so I'm pretty sure the set is at least picking up background noise.

 

[WA8ZTZ]

If you think the receiver is working, then you should be hearing something... WWV or hams or something.
Properly tuned, a regen set is very sensitive.

An RF signal generator would be ideal but if you cannot access one then you may be able to pick up the local oscillator signal of a shortwave set if you have one, even a portable will do.

Place your regen set close by the shortwave set. Tune the shortwave set to a frequency somewhere near the center of the regen set
tuning range then slowly tune the regen set dial throughout its range and listen for the shortwave set local oscillator signal.

 

[OscarKilo]

If you think the receiver is working, then you should be hearing something... WWV or hams or something.
Properly tuned, a regen set is very sensitive.

An RF signal generator would be ideal but if you cannot access one then you may be able to pick up the local oscillator signal of a shortwave set if you have one, even a portable will do.

Place your regen set close by the shortwave set. Tune the shortwave set to a frequency somewhere near the center of the regen set
tuning range then slowly tune the regen set dial throughout its range and listen for the shortwave set local oscillator signal.

I'll see what I can come up with for generating a shortwave signal. I wonder if there is too much interference that is blocking out shortwave broadcasts in the air. All I hear is hissing and popping through the tuning range.

I've tried to educate myself the best I can on the operation of regen receivers, so that I can get the highest sensitivity. If I can confirm that the receiver is working correctly, then I will look into different antennas more.

 

[majoco]

Regens aren't the easiest things to tune and you have to set the regen control exactly right - not quite oscillating for AM stations and only just oscillating for CW - I've never tuned a regen for SSB, I don't think SSB was invented when I had my regen! The regen control is not a set-and-forget - the amount of regen feedback is dependant on the tuning so everytime you change the tuning you have to reset the regen. The popping noise you are hearing is the radio going in and out of oscillating - I think you may need to be a little more gentle with the control! I had a quick look at the ARRL notes here....

Tuning A Regenerative Receiver

The American Radio Relay League (ARRL) is the national association for amateur radio, connecting hams around the U.S. with news, information and resources.

www.arrl.org

....which seemed to sum it up quite nicely. There's probably nothing wrong with your antenna, just check to make sure you're not connected to the "Atttenuate" connection.

 

[OscarKilo]

Regens aren't the easiest things to tune and you have to set the regen control exactly right - not quite oscillating for AM stations and only just oscillating for CW - I've never tuned a regen for SSB, I don't think SSB was invented when I had my regen! The regen control is not a set-and-forget - the amount of regen feedback is dependant on the tuning so everytime you change the tuning you have to reset the regen. The popping noise you are hearing is the radio going in and out of oscillating - I think you may need to be a little more gentle with the control! I had a quick look at the ARRL notes here....

Tuning A Regenerative Receiver

The American Radio Relay League (ARRL) is the national association for amateur radio, connecting hams around the U.S. with news, information and resources.

www.arrl.org

....which seemed to sum it up quite nicely. There's probably nothing wrong with your antenna, just check to make sure you're not connected to the "Atttenuate" connection.

Good advice! I think I need to get some bigger knobs for the three PCB mount pots, I'm pretty much just turning the shaft, making it very hard to fine tune the receiver.

 

[majoco]

Good idea! Take the radio with you when you shop for the knobs, there are many varieties of pots with different diameters and number of splines!

Oh - and welcome to RR!

 

[OscarKilo]

I found this neat tutorial on building a loop antenna in the wiki on this website: A Magnetic Loop Antenna for Shortwave Listening (SWL) - KR1ST

I might build it just for fun and see if it works with my receiver. Certainly would be more convenient than stringing my long random wire!

 

[majoco]

So you want to introduce yet another knob to twiddle so you can lose the signals in another way! String up your long wire - it doesn't need tuning and will be broad band over the frequency range of your receiver. Listen in the evening after dark, set the main tuning somewhere around the centre of its travel, turn the audio to about 75% full, increase the regen until you hear an increase in the noise but no a plop of going in to oscillation, now tune the fine tuning from one end to the other slowly. If you don't hear anything, tweak the main tuning a tiny bit, readjust the regen and try again. There should be heaps of signals from 9MHz to 15MHz in the late afternoon and 5.5MHz to 10MHz in the evening.

 

[OscarKilo]

So you want to introduce yet another knob to twiddle so you can lose the signals in another way! String up your long wire - it doesn't need tuning and will be broad band over the frequency range of your receiver. Listen in the evening after dark, set the main tuning somewhere around the centre of its travel, turn the audio to about 75% full, increase the regen until you hear an increase in the noise but no a plop of going in to oscillation, now tune the fine tuning from one end to the other slowly. If you don't hear anything, tweak the main tuning a tiny bit, readjust the regen and try again. There should be heaps of signals from 9MHz to 15MHz in the late afternoon and 5.5MHz to 10MHz in the evening.

Yes, I can never have enough knobs to fiddle with! Hahaha! That's a good suggestion, I keep trying to find signals with the coarse tuning knob, but the signals might be too narrow to find with it. Do the lower shortwave frequencies come in better the later it gets into the night, or is late afternoon/early evening the best time?

 

[OscarKilo]

Oh boy, I think I actually picked something up last night! It was faint, but I could hear some SSB. I couldn't modulate it to make it intelligible, but it sounded like speech. I think it was in the 40 meter band. My new loop antenna is what picked it up, it took a lot of knob twisting to tune in. Regen receivers definitely take some skill to tune. I will try again tonight and see if I have any more luck! Thanks for the tips on tuning majoco, I think I'm getting the hang of it now.

 

[WA8ZTZ]

Oh boy, I think I actually picked something up last night!

That is encouraging.
A regen set has to be tuned slowly and carefully but you really should be hearing all kinds of signals.
Have you tried taking the radio to another location? Maybe there is some local interference that is
covering the desired signals. Otherwise, is there perhaps a local ham radio club that may be able to
help you to determine that the set is properly peaked up. They may have somebody who has a RF
signal generator.

 

[OscarKilo]

That is encouraging.
A regen set has to be tuned slowly and carefully but you really should be hearing all kinds of signals.
Have you tried taking the radio to another location? Maybe there is some local interference that is
covering the desired signals. Otherwise, is there perhaps a local ham radio club that may be able to
help you to determine that the set is properly peaked up. They may have somebody who has a RF
signal generator.

I'm finding the circuit to be somewhat unstable, it tends to drift easily once I've tuned it. There is a lot of electrical noise in the room I'm using it, so it probably would be worth trying other locations, even outside. Interestingly, when the antenna and receiver are tuned to the same frequency, and I hold the antenna close to the receiver, it feeds back and makes quite a lot of squealing. Mine is in a plastic case, metal probably would've been a better idea for shielding. Oh well, hopefully with more practice I'll pull in more signals.

 

[majoco]

The whole idea of a regenerative receiver is that with a little bit of feedback from the output of the RF amplifier back to the input you can reduce all the lossy parts like the inefficiences of the transformer and increase the gain of the amplifier - but increase it too much and you get too much feedback and you make an oscillator - after all that's all an oscillator is, some amplification and a bit of feedback from output to input. Ever held a microphone in front of a speaker and amplifier? You get "howl round"! So that's all you're doing with your loop antenna and the radio - the loop is picking up a signal from the output of the radio.

There is a lot of electrical noise in the room I'm using it, so it probably would be worth trying other locations, even outside.

Yes, definitely. The noise comes from switch mode power supplies (wall warts!), flourescent light ballasts, motors, TV's, computers, monitors, printers and their power supplies, all sorts of things, so go round and turn off what you can - turn them off at the wall, not just the power on/off switch. I hope you are running the radio from the 9 volt battery, not a power supply!

 

[OscarKilo]

Yes, definitely. The noise comes from switch mode power supplies (wall warts!), flourescent light ballasts, motors, TV's, computers, monitors, printers and their power supplies, all sorts of things, so go round and turn off what you can - turn them off at the wall, not just the power on/off switch. I hope you are running the radio from the 9 volt battery, not a power supply!

I'm using a 12v dc power supply, but I'm also connecting the receiver ground to earth through the mains wiring. I think with that in place it keeps the hum down. I try to turn off any other wall warts in the vicinity though.

The tricky part with the receiver is getting the most regen before oscillation, again bigger knobs will be my solution there. I think I picked up some CW Morse code the other night, but trying to set the regen so it would come in clearly was a challenge.

 

[majoco]

If you have another portable radio with SW bands, try wandering around your house looking for the noise sources. My washing machine puts out a lot of hash even when not in use - I have to turn it off at the wall socket.

 

[WA8ZTZ]

I'm using a 12v dc power supply, but I'm also connecting the receiver ground to earth through the mains wiring.

Do not use the 12 volt power supply... try running direct off of a battery.
Also, not sure what you mean about "ground to earth through the mains wiring".
Stay away from the house wiring.

 

[OscarKilo]

Do not use the 12 volt power supply... try running direct off of a battery.
Also, not sure what you mean about "ground to earth through the mains wiring".
Stay away from the house wiring.

I connect the ground post on the receiver to the center screw (which is earthed in my case) on the wall outlet to properly ground the receiver. I'l try a 9v battery, but I don't think the power supply contributes too much noise.

I've also been thinking about getting an up converter for my SDR receiver so I can see if it will receive shortwave.

 

[majoco]

Yes, but that ground wire runs parallel to the power cables for a fair distance and those power cables are connected to every noise source in your house. Yes, I know they are insulated from each other so can't introduce noise - BUT THEY CAN and do! A capacitor passes AC current and the higher the frequency the more gets through - a capacitor is made from two conductors with insulation between them - just like your ground wire and the power wire.... and the same as your 12volt power supply! Your radio is designed to pick up minute signals - 50 millionths of a volt is a strong signal - so is easily masked by your locally generated noise - get rid of the noise first!