We seek to understand and document all radio transmissions, legal and otherwise, as part of the radio listening hobby. We do not encourage any radio operations contrary to regulations. Always consult with the appropriate authorities if you have questions concerning what is permissable in your locale.

Author Topic: New here, and my journey building a SW xmtr  (Read 2547 times)

Offline fieldstrength1947

  • Newbie
  • *
  • Posts: 18
    • View Profile
New here, and my journey building a SW xmtr
« on: September 20, 2018, 1907 UTC »
Hello everyone, I'm new here on the board but definitely not new to radio experimentation, broadcasting, and electronics work.

I have plenty of experience on AM and FM with legal power levels, i.e. Part 15 and squeezing as much range as possible out of such systems. Recently though I've gotten interested in SW broadcasting. After doing a lot of research I've decided as a first project to try to build an AM modulated Michigan Mighty Mite, as described here: https://makerf.com/posts/so_you_want_to_be_a_shortwave_pirate

Half a watt ought to be plenty for me to mess around with for now. I don't want to go overboard. Don't have the resources to deal with the possible repercussions of yet higher power levels...  ;)

Plus on SW it's much easier to make an efficient antenna on a small scale. Quarter wave at 7000 kc is 34.5 feet... not out of reach for hanging on a tree or something, just for giggles. Much better than Part 15 AM where your antenna efficiency is probably 5% or less even with the very best systems. Even 1/8 wave would probably be pretty good, right?

So I ordered up some parts from Mouser. As many crystals for different frequencies within the usual pirate bands I could find that they had in stock, plus any parts I didn't already have to make the circuit.

My question here is, anyone have suggestions for building this circuit and for SW broadcasts in general? I'm not looking for "MMM sucks, build {some other xmtr}". Any other projects can come later. Right now I'm just doing this because it's small and easy and all I have the resources and time for.

One of my specific questions I'm wondering about is whether I can put a potentiometer somewhere in the MMM circuit to vary the power output level. Ideally I'd have a mark somewhere on that dial for "legal" power with a certain antenna setup, so I could use it for micro-power broadcasts when I just want to send something to a radio in the house for fun. Unfortunately I don't have a field strength meter so it would be difficult to determine the actual legality, but I guess I could approximate by just walking around with radio.

Thanks!

Online JimIO

  • Sr. Member
  • ****
  • Posts: 255
  • QTH I.O. MA
    • View Profile
Re: New here, and my journey building a SW xmtr
« Reply #1 on: September 21, 2018, 0425 UTC »
Seriously dude? Half a watt? Nobody is gonna hear you!

Edit

That was rude of me. You could use a variable power supply and run it at less than 12 volts. You could make a Variable RF attenuator from a potentiometer and a resistor.
There is a name for the circuit but I can't remember or find it now. I would look at the Chinese Pixie kit on ebay. For about $4 you get a nice PCB and a bunch of parts and there is alot of info on youtube.

https://youtu.be/pgTv9E5uTyI

https://youtu.be/Hct3WHUcnuA

« Last Edit: September 21, 2018, 1928 UTC by JimIO »

Offline moof

  • Full Member
  • ***
  • Posts: 205
    • View Profile
    • Email
Re: New here, and my journey building a SW xmtr
« Reply #2 on: September 21, 2018, 2047 UTC »
Those riceburners don't support audio input just cw right?  Let's not take a steaming load on this.  Didn't channel z do the experiment like 25watts/10 watts/1 watt during a broadcast and there was a slight decrement each time?  The lowest power was still listenable.  I bet he had a nice high dipole.  Remember this broadcasting power thing is logarithmic.  Lots more power needed to increase coverage.  I bet half a watt with a nice inverted v at the highest height you can reasonably get would perform as well as a ten watt run into a vertical or shitty nonoptimized dipole.  I say go for it and post when you will try broadcasting on the broadcast thread.  If you can do breadboard shit go for it but I take the easy way out and would try copper board manhattan style coz that's the way I think and might work better.  Just my 2 cents.  Go ahead and yall rec.pets.cats flamewar on me.  I encourage you to build that sob and learn from it.
PS yeah I miss alt.tasteless back in the day.
« Last Edit: September 21, 2018, 2054 UTC by moof »

Online JimIO

  • Sr. Member
  • ****
  • Posts: 255
  • QTH I.O. MA
    • View Profile
Re: New here, and my journey building a SW xmtr
« Reply #3 on: September 21, 2018, 2227 UTC »
I looked again for that variable attenuator circuit but can't find it. It is just a 200 ohm pot and a 51 ohm resistor. The input is the wiper of the pot. The resistor goes from one end of the pot to ground. The other end of the pot is output. More at Wikipedia:

https://en.wikipedia.org/wiki/Attenuator_(electronics)

Offline KaySeeks

  • Hero Member
  • *****
  • Posts: 611
    • View Profile
Re: New here, and my journey building a SW xmtr
« Reply #4 on: September 21, 2018, 2355 UTC »
I bet half a watt with a nice inverted v at the highest height you can reasonably get would perform as well as a ten watt run into a vertical or shitty nonoptimized dipole.

It's a question of management of expectations. If you aren't expecting VOA-levels of coverage then you may find it satisfactory.  ;)

I think that The Relay Station runs 1/2 W into a "good" antenna during the daytime occasionally and people actually do hear it.


If you can do breadboard shit go for it but I take the easy way out and would try copper board manhattan style coz that's the way I think and might work better. 

I prefer dead-bug style - shortest connections between components in some cases.
Just somebody with a radio, a computer and a pair of headphones...

Offline ChrisSmolinski

  • Administrator
  • Marconi Class DXer
  • *****
  • Posts: 22081
    • View Profile
    • Black Cat Systems
Re: New here, and my journey building a SW xmtr
« Reply #5 on: September 22, 2018, 0027 UTC »
I think that The Relay Station runs 1/2 W into a "good" antenna during the daytime occasionally and people actually do hear it.

Indeed. I think sometimes even with less power  ;D

One S unit is a power ratio of 4. Signals can be heard at even very low transmitter power levels.
Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
NRD 545 / netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 670 ft horizontal loop / 500 ft northeast beverage / 270 ft west-south-west beverage / 300 ft south beverage / 43m / 20m / 10m  dipoles / Crossed Parallel Loop

Offline didu heardat

  • Jr. Member
  • **
  • Posts: 39
    • View Profile
Re: New here, and my journey building a SW xmtr
« Reply #6 on: September 22, 2018, 0248 UTC »
I think that The Relay Station runs 1/2 W into a "good" antenna during the daytime occasionally and people actually do hear it.

Indeed. I think sometimes even with less power  ;D

One S unit is a power ratio of 4. Signals can be heard at even very low transmitter power levels.
you should know Chris because you hear damn near everything.
including a MMM doing a half watt at least a few times. i know that for a fact.
i also know that you and most everyone else has been hearing higher power MMM's for years.

i think the MMM is just fine. making more power out isn't that hard either.
with or without a added rf section filter the output or you'll be throwing harmonics everywhere.
the output level of the MMM is affected by how well you tune the variable capacitor if you build it with one instead of a fixed value.
i could add add a bit more but if you build it you'll learn. it's part of the FUN.

so try it you'll more than likely like it . you can always build something else later.




« Last Edit: September 22, 2018, 0251 UTC by didu heardat »

Offline Stretchyman

  • Sr. Member
  • ****
  • Posts: 349
    • View Profile
Re: New here, and my journey building a SW xmtr
« Reply #7 on: September 22, 2018, 0845 UTC »
If you Solder I can send you a PCB at min cost, or I can built it for you.

Have 3W, 10W, 40W & 150W designs.

I'm not a fan of dead bug construction as PCBs are so cheap!

Str.

p.s. why bother with 0W5? pointless unless you're TXing CW or you want no-one to hear you!. 10W is fine. No you cant adj pwr with a pot, again pointless, just operate from less volts. Nothing Legal about any power level on the freqs you suggest either!
« Last Edit: September 22, 2018, 1128 UTC by Stretchyman »
'It's better to give than receive' so why RX when you can TX!

                            Buy one from me, NOW!

Great discounts on ALL my transmitters if purchased via HFUnderground


                                              ;)

Online Josh

  • DX Legend
  • ******
  • Posts: 2518
    • View Profile
Re: New here, and my journey building a SW xmtr
« Reply #8 on: September 22, 2018, 1931 UTC »
Those riceburners don't support audio input just cw right?  Let's not take a steaming load on this.  Didn't channel z do the experiment like 25watts/10 watts/1 watt during a broadcast and there was a slight decrement each time?  The lowest power was still listenable.  I bet he had a nice high dipole.  Remember this broadcasting power thing is logarithmic.  Lots more power needed to increase coverage.  I bet half a watt with a nice inverted v at the highest height you can reasonably get would perform as well as a ten watt run into a vertical or shitty nonoptimized dipole.  I say go for it and post when you will try broadcasting on the broadcast thread.  If you can do breadboard shit go for it but I take the easy way out and would try copper board manhattan style coz that's the way I think and might work better.  Just my 2 cents.  Go ahead and yall rec.pets.cats flamewar on me.  I encourage you to build that sob and learn from it.
PS yeah I miss alt.tasteless back in the day.

Agreed, a dipole is an excellent antenna, almost impossible to improve or beat their efficiency with something as simple. A horizontal dipole within 400 miles of a certain smolinksi would ensure plenty of nvis signal coverage, if you want folks to copy further away, see if you can rig up a vertical dipole.
Conveniently located near Vincennes Indiana.

Offline ChrisSmolinski

  • Administrator
  • Marconi Class DXer
  • *****
  • Posts: 22081
    • View Profile
    • Black Cat Systems
Re: New here, and my journey building a SW xmtr
« Reply #9 on: September 22, 2018, 1953 UTC »
I think that The Relay Station runs 1/2 W into a "good" antenna during the daytime occasionally and people actually do hear it.

Indeed. I think sometimes even with less power  ;D

One S unit is a power ratio of 4. Signals can be heard at even very low transmitter power levels.
you should know Chris because you hear damn near everything.
including a MMM doing a half watt at least a few times. i know that for a fact.
i also know that you and most everyone else has been hearing higher power MMM's for years.

I believe I've heard Relay Station when he's running 100 mW or so. If you do the math, it's not too surprising, assuming you have decent conditions. Since you only lose an S unit per factor of 4 power reduction, you can go from 10 watts carrier to 625 mW, just over half a watt, and only lose 2 S units. 150 mW is only another S unit below that.  You need very low noise levels to hear anything, though. Both atmospheric and local.  The 22 meter beacons typically run 4 mW, as another example of low power. Of course this is CW not AM.
Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
NRD 545 / netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 670 ft horizontal loop / 500 ft northeast beverage / 270 ft west-south-west beverage / 300 ft south beverage / 43m / 20m / 10m  dipoles / Crossed Parallel Loop

Online JimIO

  • Sr. Member
  • ****
  • Posts: 255
  • QTH I.O. MA
    • View Profile
Re: New here, and my journey building a SW xmtr
« Reply #10 on: September 22, 2018, 2340 UTC »
The whole reason for using shortwave is to use skywave propagation and to broadcast rock music mostly from the late 60's to early 70's.

Offline redhat

  • DX Legend
  • ******
  • Posts: 1089
  • "It looks like green bacon in the sky"
    • View Profile
    • Email
Re: New here, and my journey building a SW xmtr
« Reply #11 on: September 23, 2018, 0027 UTC »
The whole reason for using shortwave is to use skywave propagation and to broadcast rock music mostly from the late 60's to early 70's.

Says who?  ::)
Somewhere under the stars...
WinRadio Excalibur/305 w/ a chi-town resonant loop, Kenwood KDC-U356 for mobile listening.
Please send QSL's and reception reports to xfmshortwave [at] gmail [d0t] com

Offline fieldstrength1947

  • Newbie
  • *
  • Posts: 18
    • View Profile
Re: New here, and my journey building a SW xmtr
« Reply #12 on: September 23, 2018, 0027 UTC »
Thanks for all the help and advice, everyone!

Last night and this morning I built the transmitter. It looks quite nice in its little weatherproof exterior box. I put terminals on the outside of it for the crystal so it's easy to change frequencies.

And it works, first try too; I didn't have to change anything. The signal is clean and clear, with only a little hum. Handles reasonably loud audio levels nicely.

I hooked it up to 18 feet of 18 gauge bare copper wire (about 1/8 wave) as a test antenna, to see what it does in the daytime. Goes about a mile... not too bad, I guess. The same as my Part 15 AM setup, though. I just have the wire hanging from a tree straight up and down. (the initial tests were done with a 3 foot whip antenna and the range was about a block.) Putting a second 18 foot length on the ground terminal 90 degrees to the vertical changed nothing.

So I guess now I need advice for antennas... what would y'all recommend for antennas? I've heard a lot about the inverted V type. If I were to build one, what ought I to build it out of? Does it need to be something very thick, like copper tubing, or could it just be thick gauge wire?

I'm a little in the dark as to shortwave antenna design. Also, how crucial is grounding? I can ground it well if I need to but will it make a difference range-wise?

Offline didu heardat

  • Jr. Member
  • **
  • Posts: 39
    • View Profile
Re: New here, and my journey building a SW xmtr
« Reply #13 on: September 23, 2018, 0117 UTC »
cool you got it going .
there will be some who disagree with this.
i used a dipole as a inverted v just high enough to keep the ends off the ground about a foot .
and no earth ground .
1/2 watt carrier approx. was heard last night by ChrisSmolinski and it wasn't in his backyard by a long shot.
 no location will be provided so don't ask.
https://www.hfunderground.com/board/index.php/topic,46168.0.html

Offline redhat

  • DX Legend
  • ******
  • Posts: 1089
  • "It looks like green bacon in the sky"
    • View Profile
    • Email
Re: New here, and my journey building a SW xmtr
« Reply #14 on: September 23, 2018, 0650 UTC »
Antenna choice usually boils down to several factors; your intended audience and their location, your location, and your available real estate.  If you want to reach most of the DX'ers in this country, your aiming for the east coast.  If your close enough to the east coast to hit it with a dipole or inverted V via NVIS, then that's all you'll need.  If your closer to the mid section or west of the country and want to hit the same people, a vertical would be a better choice as it focuses more radiated power toward the horizon.

The down side to hitting the coast from the coast is that your limited to the hours when NVIS is effective, usually during daylight hours to just after sunset.  This will be influenced by solar activity, and there will be times even during the day that NVIS is not possible on 43 meters, like when the MUF is low.  Likewise, skywave (on 43 meters anyway) is best during dark hours.

+-RH
Somewhere under the stars...
WinRadio Excalibur/305 w/ a chi-town resonant loop, Kenwood KDC-U356 for mobile listening.
Please send QSL's and reception reports to xfmshortwave [at] gmail [d0t] com