Link Coupled Tuner Completed

[ka1tdq]

I just completed a link coupled tuner for 75 meters and hooked it up to a (roughly) flat-top dipole fed with 100 feet of ladder line.  I get the SWR down to 1.7:1, and I could probably get it lower but my output coil has a bit to be desired and I could probably remove one turn from the input coil.  BUT, the SWR is low enough that I can feed it with my tube amp with no problems whatsoever. 

Speaking of which, I've attached a photo of my single 3-500 amp progress.  All I need to do now is complete the wiring and build an RF-sense relay to switch the receiver coax in and out. 

As shown in the photo, my QRP AM transmitter and IRF-510 push-pull amp put out 14 watts carrier with plenty of upward mobility for positive peaks.  I broke down and bought a good Heil microphone and the better Radio Shack microphone mixer to drive the transmitter.  It sounds much better than my homebrew electret mic with an opamp as a driver. 

Jon
KA1TDQ

[ka1tdq]

...and actually here's a couple better shots of the amp progress.

[flintstone mop]

hmmmmmmm try to change direction to a pair of 3-500's. At least you will be able to get more juice into the aerial.
A Single 3-500 will make 1kw PEP.........about 125W carrier for A.M.
Fred

[aa5wg]

Jon,

You have a very nice looking link antenna coupler and amp.

Chuck

[ka1tdq]

That's true.  I have enough juice everywhere to support two tubes.  Let me ask my wife.  All I need to do is drill another hole for the tube socket and get another tube.

Jon

[KA0HCP]

Very good!  Hand built and handy!

[K1JJ]

I just completed a link coupled tuner for 75 meters and hooked it up to a (roughly) flat-top dipole fed with 100 feet of ladder line.  I get the SWR down to 1.7:1, and I could probably get it lower but my output coil has a bit to be desired and I could probably remove one turn from the input coil.  Jon
KA1TDQ

Hi Jon,

You should be able to get the swr down to 1:1 in most cases.   Looking at your link tuner tuner I see you are not able to tap the feeders and vacuum cap anywhere you wish.

Start with a coil that is not connected to anything. The input link is fine as it is.  Put alligator clips (or flat clips are better) on the antenna leads and vacuum cap. This gives you two pairs of connections that will allow you to find a 1:1 swr.    No need to short the coil.

Sometimes the antenna leads need to go closer to the middle and sometimes farther out. Always keep all tap pairs balanced. IE, tap onto the same amount of turns on each side of the coil for a given pair.... keep everything balanced.  The cap and ant leads will usually be on different points - or once in awhile attached to the same points as your tuner is now.

There is also a series configuration if you happen to run across a low impedance feed situation.  I posted a schematic of it somewhere on this BB.  You can easily jumper that tuner between parallel and series feed if need be.

Flexibility is all about having a lot of choices... :-)


T

[ka1tdq]

Sounds good on the tuner and it's an easy fix.  I thought about that while I was building it but went with the current configuration for construction ease.  I'll swap the aligator clips out too with flat surface ones.  My SWR has drifted and this may be contributing to the problem.

I'm also going to finish the amp with the single tube for now since I already have all the parts.  I'm also looking to get my hands on a cheap receiver. I have a Softrock Ensemble II kit, but can't quite bring myself to build it yet... soooo boring! 

I do have a Linux based computer though running Ubuntu.  If someone knows of a cheap USB receiver out there (built from the factory) and instructions on how to move the frequency down to 75 meters with the Linux code, that'd be awesome too.

Jon

[KB2WIG]

J,

Well, you could try to find a somewatt local online receiver...... 


http://www.globaltuners.com/

For AZ           
http://www.globaltuners.com/receiver/59/

klc

[ka1tdq]

That is totally awesome!  I just applied for an account.  All I would need to do is build a relay to mute my computer during TX.  I can also monitor my transmitted test signals.  Thanks!!!

[ka1tdq]

I found a low voltage lighting transformer at Goodwill for $3. The ratings are 12 volts at 300 watts (or 25 amps). I am going to attempt to rewire it for 5.0 volts and get 30 amps for the filament on two tubes.

[ka1tdq]

I made the changes to the tuner and now the SWR is down to 1.2:1.  Good enough.

I'm also going to get the new Alinco receiver later in the week.  It's a regular radio and has an I/Q output which can be used with SDR software for a spectrum analyzer display.

AND, I'm getting the second 3-500 tube next week.

Finally, I'm going to use a beverage antenna on receive and use the separate flat-top dipole for transmit.

I'm hoping to be on the air (in style) in less than a month.