Corsair transmitter PCB made up

Everything technical about radio can be discussed here, whether it's transmitting or receiving. Guides, charts, diagrams, etc. are all welcome.
Post Reply
Gigahertz
no manz can test innit
no manz can test innit
Posts: 212
Joined: Fri May 08, 2015 6:42 pm

Corsair transmitter PCB made up

Post by Gigahertz » Sun Apr 25, 2021 10:40 am

With the help from ZoZo got PCB's made up for the "Corsair" transmitter

This will save on build time and make them look alot neater!

Left hand side board is 6KHz compressor/limiter. Right hand side is the Corsair
You do not have the required permissions to view the files attached to this post.

User avatar
Zozo
no manz can test innit
no manz can test innit
Posts: 220
Joined: Sun Feb 14, 2021 9:33 am
Location: 3rd rock from the Sun

Re: Corsair transmitter PCB made up

Post by Zozo » Sun Apr 25, 2021 12:07 pm

You got those pretty quick, JLC does produce good quality PCB's. I'm waiting for Dave Martins thought's when he see's it ;)
~Give me a transmitter with things that glow any day!

Albert H
proppa neck!
proppa neck!
Posts: 1911
Joined: Tue Apr 05, 2016 1:23 am

Re: Corsair transmitter PCB made up

Post by Albert H » Sun Apr 25, 2021 11:15 pm

That's quite amusing. The audio processor was my design from many years ago! If built as described, the audio filter applies a bit of "mid boost" to brighten the audio a bit, and then there's a 6kHz lowpass filter to keep the modulation reasonably tight. The compressor part is pretty much a "cookbook" circuit using a couple of op-amps and an FET as the variable gain element.

There is a small improvement that can be made to the compressor, to reduce distortion - connect a 1MΩ resistor in series with a 100n cap between the drain and the gate. This applies a bit of the audio to the FET gate, and helps to reduce the distortion (particularly at around 6dB gain reduction).

I always used to throw these processors together on a bit of Veroboard. I think that I've got the layout here somewhere - I'll post it when I find it.

Incidentally, it's NOTHING like an "Optimod". The Orban processor uses multi-band processing and aggressive clipping to give a really tightly controlled modulation level. They always sound HORRIBLE!
"Why is my rig humming?"
"Because it doesn't know the words!"
;)

User avatar
Zozo
no manz can test innit
no manz can test innit
Posts: 220
Joined: Sun Feb 14, 2021 9:33 am
Location: 3rd rock from the Sun

Re: Corsair transmitter PCB made up

Post by Zozo » Sun Apr 25, 2021 11:35 pm

That's interesting regarding the modification for reduced distortion, maybe that will have to be implemented on a new revision.

Sadly I no longer have the original schematic I was sent to work from. I think Gigahertz will have to post that to see if it's a 1:1 copy of yours.
All I do know is that it was called "A Very Poor Mans Optimod", hence the AVPM anacronym. There was no other name(s) to credit onto the PCB from the schematic.

Be nice if you can locate and share your original Veroboard design.
~Give me a transmitter with things that glow any day!

User avatar
sinus trouble
proppa neck!
proppa neck!
Posts: 818
Joined: Fri Aug 22, 2014 11:34 pm

Re: Corsair transmitter PCB made up

Post by sinus trouble » Mon Apr 26, 2021 12:41 am

Great work Gigahertz :)

I have never really delved into the realms of AM? But this looks interesting?

I am guessing the frequency of operation is determined by the crystal selected?
I am as stupid as I look! :|

User avatar
reverend
big in da game.. trust
big in da game.. trust
Posts: 99
Joined: Sat Jul 25, 2020 12:03 pm

Re: Corsair transmitter PCB made up

Post by reverend » Mon Apr 26, 2021 9:17 am

Nice work GHz - be interested to know what power you get out of that. I always used a 74HC240 to drive the gate of a FET for SW tx rather than the (I think BFY51) that the Corsair uses. I found you got more power, and less heat. I'll have to dig out a schematic and post it here.

Rev
if it ain't broke, keep tweaking

Gigahertz
no manz can test innit
no manz can test innit
Posts: 212
Joined: Fri May 08, 2015 6:42 pm

Re: Corsair transmitter PCB made up

Post by Gigahertz » Mon Apr 26, 2021 12:05 pm

sinus trouble wrote:
Mon Apr 26, 2021 12:41 am
Great work Gigahertz :)

I have never really delved into the realms of AM? But this looks interesting?

I am guessing the frequency of operation is determined by the crystal selected?
Yep uses a crystal but from what research I have done, people have also made VFO circuits and Dave did share the design somewhere. I remember it did use TOKO can which may be obsolete now, if I find the schematic I’ll post it on here.

Gigahertz
no manz can test innit
no manz can test innit
Posts: 212
Joined: Fri May 08, 2015 6:42 pm

Re: Corsair transmitter PCB made up

Post by Gigahertz » Mon Apr 26, 2021 12:18 pm

reverend wrote:
Mon Apr 26, 2021 9:17 am
Nice work GHz - be interested to know what power you get out of that. I always used a 74HC240 to drive the gate of a FET for SW tx rather than the (I think BFY51) that the Corsair uses. I found you got more power, and less heat. I'll have to dig out a schematic and post it here.

Rev
Thanks Rev, but I don’t want to take all the credit for this! ZoZo helped turn this idea into reality.

I have built a number of Dave Martin’s transmitters on copper cladding. All using genuine parts and with the Corsair get 10w carrier. The only time I’ve notice excessive heat on the BFY51 is when I built the Commando circuit.

I’ve seen 74HC*** being used in the LuLu but not studied the circuit as of yet.

So far the best distance with a Corsair (was weak signal but people where able ID the track) East coast of the States. So not bad low power.

Please share your circuit when you come across it.

Albert H
proppa neck!
proppa neck!
Posts: 1911
Joined: Tue Apr 05, 2016 1:23 am

Re: Corsair transmitter PCB made up

Post by Albert H » Mon Apr 26, 2021 11:06 pm

It's quite close to the old medium wave circuit I used to build. I used a TDA2030 as the series modulator, and got roughly 12 Watts carrier from a car battery supply. I used a simple 3-chip PLL with a 4.608MHz rock (a standard frequency cheaply available from Farnell or CPC) instead of the VFO. These little rigs - into a "tower block sloper" aerial - would cover a significant area in the daytime!

I'll dig out the Veroboard layouts......
"Why is my rig humming?"
"Because it doesn't know the words!"
;)

Gigahertz
no manz can test innit
no manz can test innit
Posts: 212
Joined: Fri May 08, 2015 6:42 pm

Re: Corsair transmitter PCB made up

Post by Gigahertz » Sat Jun 05, 2021 11:30 pm

Evening Necks,
This project got put on the back burner due to other commitments, so this weekend I finally had the time to sit down and populate
both boards and put them under test. Works extremely well and sounds pretty good especially with the matching 6KHz compressor limiter.

If your interested in a set of boards (only 4 left) let me know via pm. I can also supply BF245a & BFY51 if required and be ordering some more boards soon.

Many thanks to Dave Martin for sharing the design and thanks to ZoZo for the PCB layout
You do not have the required permissions to view the files attached to this post.

MiXiN
proppa neck!
proppa neck!
Posts: 570
Joined: Sun Sep 07, 2014 4:20 pm

Re: Corsair transmitter PCB made up

Post by MiXiN » Sun Jun 06, 2021 12:15 am

Looks smashing that GHz.

Loving some of the recent projects on here recently, and it makes a nice change as it went a little quiet at one point.

Albert H
proppa neck!
proppa neck!
Posts: 1911
Joined: Tue Apr 05, 2016 1:23 am

Re: Corsair transmitter PCB made up

Post by Albert H » Sun Jun 06, 2021 12:27 pm

I have a little PLL oscillator design here that works extremely well with this type of transmitter circuit. There are two versions - one using 74HC logic and the other using the MC145106. Both use the same Colpitts oscillator circuit and provide a nice buffered sinewave output.

I've also used "huff & puff" stabilisers for tunable rigs. If you design for (say) 6.2 - 6.4 MHz, you can make the controlled VCO tune in 100Hz "jumps" - you need a counter to set the output frequency, but it's "set and forget" until you restart the transmitter for the next broadcast. I've found this to be useful to avoid "QRM" from other stations, fax transmissions and other data modes.

Shortwave AM is interesting - I've done it intermittently since the late 60's - and in all that time I only "lost" about sixteen rigs!

Nice boards, by the way GHz!
"Why is my rig humming?"
"Because it doesn't know the words!"
;)

Post Reply