MFJ-933 Loop Tuner
- Hi - all. I've been searching for an antenna that will do a decent job in
my weird little space. I'm in a 35' x 35' with buildings 10 feet away in
each direction. There are power, catv and phone cables crossing in all
directions at about 10 feet. I'm hoping a small loop will do it for me.
I'm curious if anybody has experience with the MFJ-932 tuner? (I only run
5 watts QRP so the 50 watt limit is no problem.) Looks like a cheap way to
test loops at under $100.00, new. I have no variable capacitors so I'll be
buying, no matter what I decide to try. Opinions and alternatives
San Diego CA
- Hi Kip,
This is the first I've seen the new MFJ-932 loop 'tuner'. I saw the other QRO
loop tuners when they first came out but decided they were too pricey for my
budget (and a little large for my portable QRP set up).
Here's a link to the tuner's manual on MFJ's website:
Keep in mind, that by running QRP into a really short loop (1/10 wavelength),
that you will be operating QRPp (<1 W ERP). The reason most folks have alot of
success with the small loops is because they are running 50-100 watts with an
ERP (Effective Radiated Power) of 5-25 Watts. Also, realize that the further
away from metal objects you can get the loop, the better it should perform.
If $100 isn't going to break you financially, it might be alot of fun to try.
Keep in mind that the tuning is going to be quite sensitive for very short
loops (longer loops approaching 1/4 wavelength shouldn't be too difficult to
tune), and I have no way of determining if this tuner has some sort of 'venier'
drive which would make it easier to fine tune for the frequency you want to
operate on. This could make tuning your loop every time you change frequencies
a real pain.
Also, you didn't specify which bands you intend on using with this setup. The
manual on MFJ's website suggest best efficiency is achieved when using a wire
about 1/4 wave long for the desired frequency. For 40m, that would be about 33
ft. A square loop mounted inside along a wall might work fine for this (roughly
8x8 ft). They recommend using heavier gauge wire (#10). Even larger conductors
... maybe even aluminum foil - would result in greater efficiency, but that is
quite fragile mechanically. Aluminum flashing is another heavier duty
possibility along with flexible copper tubing - but that would be difficult to
If you are a daytime QRP operator, you could probably have the most fun trying
out the tuner on 20m with a small 4x4 loop made from #10 solid wire. This is
small enough to be easily mounted behind a bookcase or out of sight in a
I'm in the same boat you're in ... no capacitors to mess around with (my
attempt at building a loop antenna involved cutting a piece of coax to length
for a capacitor). This looks like exactly the kind of thing I'd want in my bag
of tricks when I travel with my QRP rig. If you do get it, please let me know
how well it works for you, and how you use it. I'm very interested to know the
--- w6kip@... wrote:
> Hi - all. I've been searching for an antenna that will do a decent job in
> my weird little space. I'm in a 35' x 35' with buildings 10 feet away in
> each direction. There are power, catv and phone cables crossing in all
> directions at about 10 feet. I'm hoping a small loop will do it for me.
> I'm curious if anybody has experience with the MFJ-932 tuner? (I only run
> 5 watts QRP so the 50 watt limit is no problem.) Looks like a cheap way to
> test loops at under $100.00, new. I have no variable capacitors so I'll be
> buying, no matter what I decide to try. Opinions and alternatives
> appreciated. Thanks!
> Kip W6KIP
> San Diego CA