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Author Topic: Another helpfull site for making RF  (Read 4777 times)

Offline QRP

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Another helpfull site for making RF
« on: December 13, 2014, 1847 UTC »
Another helpfull site for making RF

http://am-transmitter.blogspot.de/

Offline ff

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Re: Another helpfull site for making RF
« Reply #1 on: December 14, 2014, 0200 UTC »
Cool, QRP!  That's a new site for me.  I see they have the Steve Quest transmitter there.  I feared that one was lost to the ages.  Thanks!
Hailing from the upstate boondocks region of the progressive paradise which once was New York State

Offline Pigmeat

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Re: Another helpfull site for making RF
« Reply #2 on: December 14, 2014, 0538 UTC »
Glad to hear about the Questmitter schematic being online. I've got a paper copy of it upstairs in the vast Pigmeat archives, but it's in one of several mystery boxes containing radio related junk.

BTW, are you the same QRP guy I used to exchange emails with years ago?

Offline QRP

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Re: Another helpfull site for making RF
« Reply #3 on: December 14, 2014, 1246 UTC »
Glad to hear about the Questmitter schematic being online. I've got a paper copy of it upstairs in the vast Pigmeat archives, but it's in one of several mystery boxes containing radio related junk.

BTW, are you the same QRP guy I used to exchange emails with years ago?

Yes Pigmeat, let's stay in touch ...

Offline Pigmeat

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Re: Another helpfull site for making RF
« Reply #4 on: December 15, 2014, 0820 UTC »
Sounds good to me. Glad to see you're still around.

Offline ff

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Re: Another helpfull site for making RF
« Reply #5 on: December 15, 2014, 2125 UTC »
BTW, are you the same QRP guy I used to exchange emails with years ago?

Methinks 'ol QRP is the same guy that used to run the aggregator site for QRP pirate transmitters a few years back.  This new site seems to have his fingerprints all over it :)  Hi QRP!
Hailing from the upstate boondocks region of the progressive paradise which once was New York State

Offline QRP

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Re: Another helpfull site for making RF
« Reply #6 on: December 16, 2014, 1021 UTC »
As a little bonus offers you will get an additional website to study
http://www.geocities.ws/raiu_harrison/mwa/tech/tech.html

Some of you probably think of this website that existed for a number of years ago but has now past away. It has been copied a number of times in different versions.

"Radio QRP - The Art of Low Power and Clandestine Operations"

http://www.oocities.org/radio107mhz/

Some other websites that are worth mentioning in this context is "Boomer" and "Lulu" state-of-the-art descriptions of transmitter with different technical solutions on the same idea.

http://www.angelfire.com/bc/radio/history.html

http://www.lu8eha.com/microhobby/microhobby.htm

Offline ff

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Re: Another helpfull site for making RF
« Reply #7 on: December 17, 2014, 1403 UTC »
Yep, same guy!  :)
Hailing from the upstate boondocks region of the progressive paradise which once was New York State

Offline Albert H

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Re: Another helpfull site for making RF
« Reply #8 on: November 07, 2018, 1213 UTC »
Cool, QRP!  That's a new site for me.  I see they have the Steve Quest transmitter there.  I feared that one was lost to the ages.  Thanks!

The site is (mostly) worthless.  It's just a collection of various diagrams from all over the 'net, many with errors so they won't work as drawn, and most of the higher frequency designs will be layout-critical, and there are no layouts provided.  Whoever put that waste of bits on the 'net doesn't have a clue about electronics - he's just collected stuff and put it on "his" blog.

Offline QRP

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Re: Another helpfull site for making RF
« Reply #9 on: November 07, 2018, 1236 UTC »
Cool, QRP!  That's a new site for me.  I see they have the Steve Quest transmitter there.  I feared that one was lost to the ages.  Thanks!

The site is (mostly) worthless.  It's just a collection of various diagrams from all over the 'net, many with errors so they won't work as drawn, and most of the higher frequency designs will be layout-critical, and there are no layouts provided.  Whoever put that waste of bits on the 'net doesn't have a clue about electronics - he's just collected stuff and put it on "his" blog.


After only two posts on the forum ...  ;D

Do it better and deliver some drawings you too!

Offline Stretchyman

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Re: Another helpfull site for making RF
« Reply #10 on: November 08, 2018, 0754 UTC »
However it was a good point possibly not very well made as there are loads of websites hosting crappy designs that have been floating about on th' net for years and are, in the main, rubbish!

Without the proper equipment and the ability to do a decent PCB layout most designs simply wont work, that and an enormous amount of disinformation that exists regarding RF related issues.

Yes, thought I'd add my 0.002p(c)'s worth and a seemless plug for anyone who'd like a kit or built SW TX from me......

Str.

 ;D



'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


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Offline Albert H

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Re: Another helpfull site for making RF
« Reply #11 on: November 10, 2018, 0117 UTC »
Hi Stretchyman

I've been using the '240 as a driver for IRFL FETs for years.  I usually use a CMOS PLL (74HC4046 for the phase comparator and the VCO, 74HC4060 for the reference, and diode-programmed 74HC4040s for the pre-set divider) and a standard crystal (usually 4 MHz because they're cheap) and can generate any frequency from <2MHz up to around 18 MHz in 5 or 10 kHz steps.  The synthesiser costs around a Fiver to make and avoids the need for expensively cut crystals (I got fed up with being asked what I wanted the "unusual" frequency crystals for!).  I've also found that it's a good idea to run the VCO at 2f, and use a 74HC74 to give an accurately 1 : 1 squarewave into the '240 buffer. 

I ran out of '240s and used a 4049 as the driver on medium wave.

I'm still messing around with various ways of modulating my rigs - for lower power (<10 Watts carrier), I've been using the TDA2040 as a "power op-amp" through a choke on to the drain of the output FETs.  I have a simple feedback compressor before the '2040, and have carefully chosen the feedback and input capacitors to shape the frequency response.  There's also a simple clipper circuit to handle the overshoots from the compressor to prevent splattery overmod.  There are even a couple of blinking LEDs to show you when the mod pot is about right - red for peaks, yellow for loud and green for OK.

The final issue is a simple and effective antenna for 6.2XX MHz and a simple matcher.  The rig itself is pretty much a "throwaway" item - if it gets removed by the authorities, there'll be another to replace it the next weekend!

I'll put the details of the synthesiser up here for everyone to use.  It saves a lot of headaches!

Offline Stretchyman

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Re: Another helpfull site for making RF
« Reply #12 on: November 10, 2018, 0948 UTC »
Nice one Albert, sounds good!

Many methods to generate a frequency.

I've had to get some software written to drive a cheap DDS I'm using.

However CARDINAL make programmable Xtals now so I'm going down that route to keep things simple.

Generating 2Xf and going thru a flip flop to get aniphase quare waves is good but modern FET drivers have s similar function so I use those now.

Keep up the good work!

Str.
'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


                                              ;)

Offline Albert H

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Re: Another helpfull site for making RF
« Reply #13 on: November 10, 2018, 1229 UTC »
I've experimented with a couple of the cheap Chinese DDS boards, and have had endless problems programming them - either with PICs or Atmel chips.  Most of the software that's around the 'net is either written for DDS ICs I've never seen, or just doesn't work!  I'd be very interested in your programmer software and details of the "cheap" DDS board you use.

The CARDINAL programmable crystal oscillators look like a good, cheap solution.  I wonder if I can get some "blanks" and programme them myself....?

I still favour my cheap 74HC CMOS approach, though.  The parts are dirt cheap, widely available, and if you're really anal about frequency accuracy, you can phase lock your PLL reference to a "standard" like the BBC 198kHz (accurate to 14 digits!) or other reference frequency station.  Incidentally, I use the 198kHz off-air to control the reference oscillator of my frequency counter, so when it reads 62XX.000000kHz, I know that the rig's bang on frequency!

Incidentally, I've been playing around with a Lulu of a rig on the bench, and 10 Watts carrier / 40 Watts peak is now pretty easy with a "car battery" supply.  On a quick test into an inverted-V dipole here in the southern Netherlands, I got reports from Switzerland, Italy, Germany, the UK, Ireland and Spain.  Signal strengths were described as "fading a bit" and pretty weak, but generally audible, and achieved S9 in Switzerland on peaks!  I'm quite astonished at the coverage attainable by such a simple (and cheap) set-up.  I used to just do Medium Wave (often through a -wave "tower-block sloper"), and got some great daytime results on pretty low power, but now I'm hooked on SW and will definitely put on something reasonably powerful over Christmas.  I had some big FETs arrive in the post this morning, and my target is 250W carrier / 1kW peak - just to prove that it can be done cheaply. 

I'm considering ways to modulate the 250W beast, and PWM looks favourite, but I'm tempted to go for Outphasing - I have an idea for a modulator that generates square waves at 135 to each other (derived from different outputs of a 8 CMOS IC).  These will provide the references for a couple of 4046 VCOs, which will be frequency modulated in phase opposition to each other by injecting the audio into the loop filters.....  This makes the PAs relatively simple - it's just the output bridge that gets tricky.  I've built outphased rigs before, but only ever with pairs of 807s or 813s in the outputs!

Offline Stretchyman

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Re: Another helpfull site for making RF
« Reply #14 on: November 18, 2018, 2107 UTC »
I have SW for AD9850 (drives the eBay PCB's) to give 64 channels + SW for AD9833 (eBay PCB's again) which will tune between 2 preset limits or simply program for single channel. Both designs are present in products I sell and as I don't own the SW I can't hand it over, sorry.

Just use the eBay kits with display etc, they use the 9850 and will be fine, surely?

The CARDINAL oscs are prod'g by digikey, no need to buy blanks, but yes you can buy a programmer. They even do a dual osc with 2 switchable frequencies...

Str.

« Last Edit: November 21, 2018, 0740 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


                                              ;)