I’ve finished my Emtech ZM-2 ATU kit and tried it out today. I had some success on tuning it by setting the variable capacitors for max noise on receive, changing the selector to tune, band select to AM on the radio, keying mic, whistling for England [silly me - confused beginner at work here] and twiddling the knobs to get the LED to dim. A bit hit and miss on returning to SSB because the HSWR warning flashed up on the radio a few times. I had my Avair SWR meter connected throughout. I haven’t yet got the knack that the many satisfied users on the internet claim.
Are any of you owners of this impedance matching unit and what are your ‘tuning’ techniques for a coax dipole please?
David M6WOW
There should not really be any tuning required for a resonant dipole fed with co-ax (slight generalisation). A co-ax-fed dipole used well away from its resonant frequency with a tuner is not recommended as the feeder losses soon become large if the antenna itself shows a large mismatch to the feeder. No problem doing this on receive however.
For good multi-band coverage, a doublet fed with open-wire line is recommended.
In reply to M6WOW:
I have had the the Zm-2 for several years now, and I can say it will tune just about anything (even the 70ft steel fire tower on top of South beacon Mountain)…not always resulting in a 1:1 match but close enough to operate.
I have found that my ZM-2 is incredibly sensitive, even the smallest perceivable twist of the tuning knob can change tuning greatly.
If you are not finding success with the tuner, you may be twisting your tuning knobs too quickly and may be missing the proper match point. Its unbelievable just how carefully you have to turn those tuning knobs not to miss anything. I have never used another tuner that was so particular in that respect.
In reply to M6WOW:
David,
It is generally easier to tune up an ATU with a continuous tone rather than whistling (and less tiring) especially when tuning is sensitive.
If the radio you are using has CW capabilities, use this to tune up with low power (on a clear frequency of course).
I am not familiar with the tuner that you have, David, but there is one principle that nobody has mentioned yet, and if you haven’t come across it then knowing it will be helpful. You will find on the lower bands that you can tune the antenna on more than one inductor setting. The trick is to find the setting that lets you tune up with the highest capacitance, higher capacitance gives broader tuning and better power transfer, whilst if you use an inductor setting that needs low capacitance then the tuning will become very sharp and you will need to retune more often as you move across the band. This is particularly noticeable on 80 metres!
I use a doublet fed with 300 ohm ribbon (a modified G2RV) and the tuning changes with the weather. I set the capacitors for three-quarter capacitance and then find the inductor setting for maximum RX noise, I then go for best SWR from tuning the capacitors and can get 1:1 on all bands, using the AM mode and minimum power. No whistling is necessary.
I use a doublet fed with 300 ohm ribbon (a modified G2RV) and the
tuning changes with the weather. I set the capacitors for
three-quarter capacitance and then find the inductor setting for
maximum RX noise, I then go for best SWR from tuning the capacitors
and can get 1:1 on all bands, using the AM mode and minimum power. No
whistling is necessary.
Hi Brian
I couldn’t see any point in whistling either, and I wonder if this
could have given ‘downward mod’ on AM and created a false dip on the
LED. I use the same method to tune up as you using AM at low power,
but I set my caps to half capacitance, peak on the roller coaster,
and then adjust the caps to max receive before finally trimming for
minimum VSWR. I use an SPC Transmatch, which has both series and
parallel capacitance ganged, and I’m wondering if this makes a
difference. What type of tuner do you use Brian?
Hi, Dave, I’d forgotten about downward mod, it’s been so long sine I operated AM!
I have an elderly MFJ-949E, a homebrew parallel match for the W3EDP for portable, and a homebrew Z-match for QRP, but these are likely to change as the fancy takes me!
I have an elderly MFJ-949E, a homebrew parallel match for the W3EDP
for portable, and a homebrew Z-match for QRP, but these are likely to
change as the fancy takes me!
Hi Brian,
Just had a look at the 949E, and as it has 200+pf on each section, and
is a T-match, you can have quite a lot of pfs in series!! I might build
one of these, or an L match, and do a comparison with the Transmatch.
In reply to G8ADD:
A little update. I needed a successful experiment to brighten the day so I made a W3EDP antenna or at least the 84 feet of wire and 17’ of counterpoise. I connected these to the ZM-2 and tuned it for max noise on receive.
I found that I’m often getting low SWR on the FT-817 without going through the tuning ritual. As Tom N2YTF said previously it’s a very sensitive tuner so a quick last check in SSB with a whistle and a rapid tiny turn on the main tuning control and SWR is reduced to no bars on the display. [I now understand what pressing PTT in AM mode does so no further whistling there!] I spoke to Heligoland lighthouse on 40m and and a one in Western Scotland on 80m then later I listened to the operators working Christian OE5HCE on Lagelsberg and just caught him saying his callsign. I switched in the ZM-2’s extra capacitance to try to tune in to a station on top band - can do better here with more practice. A W3EDP and ZM-2 is very convenient though the operating position at home ends up by the compost bin at the bottom of the garden! I’m looking for ways of reducing pack weight especially whilst rebuilding lost leg muscles. It’ll be interesting to have multiband capability in place of all that lovely flexweave dipole and coax cable that I’ve used so far.
If I have one fishing pole mast what is the best configuration for this wire antenna on a plain summit? Here the other end is fastened to the house at gutter level.
If I have one fishing pole mast what is the best configuration for
this wire antenna on a plain summit? Here the other end is fastened to
the house at gutter level.
David. I tried experimenting with an end feed with my inverted ‘V’ dipole setup. I connected all sections together in series and the two sides together at the feedpoint. This gave me a total length of about 40 metres. The two ends were tied to fully extended walking poles. I connected one end to a home-brew pi network tuner, against a much shorter insulated wire counterpoise laid on the ground and held down by a metal tent-peg at each end. The ground was damp but not squelchily so. Testing with an antenna analyser, I was able to get a match better than 1.5 : 1 on all the amateur bands up to 50MHz. Using the FT817 I had one QSO with this arrangement with TM100B (Special event station in Calais) on 14.260 for a 5/5 report. Janis then called DINNER, which signalled an end to unimportant things like radio.
I am a big fan of the W3EDP. What little I have done with mine during activations (as opposed to just general /P), I have lashed the end of it to the top of the mast that Geoff 2E0BTR uses for VHF and stuck a T-network tuner at the other end (a lot of people say you should not use a T-network with a W3EDP as its too lossy when matching those kind of impedances). That way we can have one mast and two stations. There is ample sag in the wire to compensate for any rotating of the mast Geoff needs to do to direct his beam. In fact, you were my very first contact off a W3EDP while you were out with Geoff - I was using a configuration very similar to this (of course, Geoff was not at the far end of the wire!). Don’t let the poor conditions that day put you off this useful antenna!
I have modelled the W3EDP in MMANA, if you’d like a copy of the files for it I can email them to you. I haven’t looked at them for a bit, but I seem to recall that having looked at them I concluded a more efficient setup may be to arrange the 84/85ft radiator as an inverted V (particularly on the low bands). On the empirical side, I know that Brian G8ADD does this to good effect on the hill. So far as I can gather, the “counterpoise” can go where it pleases in practice.
Its interesting to hear about your Z-match - I suspect that the next ATU I build will be of the same configuration. I’d be keen to know how it works with the W3EDP on the hill (I suspect quite well).
On a flattish summit I use the inverted V, on one occasion where the ground was steepish I set the pole below the summit on the sheltered side, ran half the wire horizontal to a rock near the summit and the other half downhill to the operating position - a “lazy” inverted V!
If you are interested in building a Z-match, a useful site is: