Using a Manual Tuner

I finally learned to use a manual tuner. It was easier than I thought, despite the instructions from MFJ being not very clear. Of course they made more sense after I figured out what I was doing.

One thing that I like about manual tuners is that they require no power supply to tune/work. They’re cheaper (and quieter) than an automatic tuner (ATU). But an automatic tuner is probably faster, especially since they remember the tuning settings for a particular frequency which is great if 1) you use the same antenna all the time 2) your antenna doesn’t move or has minimal environmental factors that cause it to go out of tune for no apparent reason. Otherwise you have to force a retune on your ATU which defeats the purpose of the memory function. I use at least 2 antennas at my QTH – a 49:1 that’s outside exposed to the elements including Colorado snow, as well as a 9:1 which is in my attic. The memory function of my tuner is therefore useless.

So here are some instructions that might make more sense to you (or remind me when I forget).

I used a MFJ tuner that has as SWR meter and some bells and whistles that might help in difficult situations like reflected power and a dummy load but the only thing you really need is a SWR meter somewhere.

The gist of it is that you want to have the maximum noise along with minimum SWR. If you have meters for Forward and Reflected Power then this can substitute or add to helping you fine-tune a decreased SWR. All other things being equal, a lower SWR means more power outputted in a particular system/setup. This can be confirmed with a field strength meter, which shows you where the rubber meets the road.

1. Connect the radio to the transceiver so-239 port
2. Connect the antenna to the antenna port
3. Move both capacitor knobs to middle/3.5
4. Move the inductor to minimum inductance
5. Turn on the radio to AM, and tune to the frequency of your choice (or right next to it if there are QSO’s). Turn up the AF to be able to listen to the static.
6. Turn your radio to 1 watt of RF power.
7. Listen to the noise and turn the inductor one click at a time until you find the loudest fuzz. There might be 1 or 2 that are the loudest. Don’t touch the inductor anymore from here on out.
8. Turn the Transmitter capacitor and move it to the highest fuzz. This might be difficult. Just take a stab.
9. Now key up and check the SWR meter on your radio or on your Tuner or SWR bridge if you have a separate one. Note the SWR. Stop transmitting. Take inventory and make sure the needle moved like you thought it would. Hopefully to 1 watt and a relatively low-ish SWR.
10. Key up again and hold it for for 15 second increments, while you turn the Transmitter capacitor while watching the SWR meter and turn it to the minimum SWR possible. If its a perfect 1.0 then you’re done.
11. If you’re not at 1.0 then key up and turn the other capacitor to try and get to minimum SWR. If you’re at 1.0 or < 1.5 then you’re done.
12. If your SWR is still high then start all over except with a different inductance – maybe the other one that sounded fuzzy. Otherwise, check your cable connections.
13. If your SWR is at 1.0 then change modes, crank up the power,  and operate. Note the Tuner settings for this frequency.
14. Keep an eye on your SWR as heat and power can modify SWR.
15. If you change frequencies then you’ll need to go back to 1 watt and repeat the process.
16. If you use 100% the same system of radio, tuner, coax, antenna, etc then you should be able to recall tuner settings for a particular frequency and start tuning (at low power) from those settings next time you operate. This is similar to the memory function of an ATU.

What do I use the dummy load for?

A dummy load is an antenna that doesn’t radiate but always gives an impedance of 50 ohms (at every frequency). It’s a diagnostic tool.

You can use it to test to make sure your connections are good up to your antenna’s feed line and beyond. When you substitute your feed line + antenna for a dummy load, instead, you should have full power going out, none being reflected back, and therefore a perfect SWR. If your SWR isn’t 1:1 with a dummy load then you have a problem between your radio and the tuner. Check your connections and everything in between (i.e. the coax that you slammed your window down on this winter).

This tuner of mine has one built in but you can buy one that you can connect to an antenna port. You could check/isolate your radio by plugging in a dummy load at the antenna port and transmitting at a low power. Your radio’s SWR meter should always read 1:1.

You can use the dummy load for other things, too.

What do I use the forward and reflected power meters for?

SWR is the ratio of forward to reflected power, always expressed as 1: something. If you have both meters (or a meter with 2 needles that cross) then you can usually get the forward power to the highest pretty quickly and then just pay attention to the reflected power while you crank your capacitors to minimize it. You’ll notice that the SWR on these meters is where the 2 needles cross. It’s just doing the math with moving parts. A meter that is telling you SWR is measuring the same 2 things, its just telling you the result of the math. Some meters can measure both things but only 1 at a time and the other one after you press a button. Same thing.

Now, the astute person will say “ae0rs, why do you need an antenna tuner for a 49:1 EFHW if its already resonant at 40,20,15, and 10 meters?”. The answer is 1) a tuner can make it tune to 30 meters. 2) as the wire moves around or is covered in snow, or gets hot or cold, the resonance changes ever so slightly, sometimes enough to make the SWR > 2 which requires a little touch-up inductance and/or capacitance to bring it back to < 1.5, keeping my finals happy and cool (my 2 Icoms have temperature sensors on the final amplifiers which is what gets damaged if your SWR is too high). Now, newer rigs roll back their power to protect their finals during high SWR (without telling you) but that means you might be outputting less power than you think, wondering why you can’t DX.

I’ve also had to tune a “resonant” 20 meter antenna. The only antenna I haven’t used a tuner on is my SuperAntenna MP1-C because if it goes out of tune (it never does – its rock solid), you just slide the loading coil a click or 2. Of course, I can’t hop bands and I hate having to plug in a nanovna to get it into tune when its freezing out, but I digress.

A few other things that are advantageous of manual tuners over ATU’s.

1. While your ATU is hunting/working, your rig is being subject to high SWR (even if its just at 1 watt). You can get pretty close to 1:1 with a manual tuner just listening to the static volume (in fact, this is how you tune many mag loops – just with your ear). Thus, subjecting your right to lower time spent in high SWR while tuning (some people pulse-key while they’re tuning instead of keying down the whole time).
2. You can tune to non-ham bands with a manual tuner to do SWL. An automatic tuner requires your rig to transmit and your rig won’t transmit out of the ham bands so you can’t use your ATU for SWL – although I’m not sure if an ATU really helps in this regard as I don’t much SWL on my ham radios.
3. Once your portable ATU battery is dead, you’re done for the day – stuck at your last tuned frequency.
4. Manual tuners can usually tune a wider range of impedances than an ATU (for a given size/class tuner).
5. Using a manual tuner is a manual skill that everyone should have. If your ATU is a black box then you should really level-up.

With all that said, my first tuner and the one that I use most because its pretty and small, is a LDG IT-100. Unfortunately, it only goes to 35 watts on digital modes like FT8 so I might have to employ my old MFJ’s to get the full 100 watts out of my 7100 without melting anything.

73,

ae0rs