The output impedance of most amateur transmitters is fifty ohms. The impedance of an end-fed wire could be anything between twenty and several thousand ohms. Neither does it change the fifty ohm output impedance of the radio to two-thousand ohms.
The AMU transforms the impedance from two-thousand ohms to fifty ohms. In other words: two-thousand ohms in, and fifty ohms out. A mains transformer transforms volts to, say, 12volts. That remains at volts no matter what you do. A poor aerial is a poor aerial, no matter what you do at the feed point. Frightening stuff? Not really. What is frightening is the misconception, the myths, surrounding this impedance matching device.
I use this with my Lower HF communications receiver which has no front end selectivity. The matching unit helps with out of band second order intermodulation problems.
The lower photo shows inside the matching unit. Shown below is the original L Match unit with Belling-Lee coax sockets and the so-called mode switch which, I believe, was wired incorrectly. I removed the rotary switch and fitted another variable capacitor to create a Pi network. See photo below. The unit can be returned to its original condition quite easily, which is important when modifying vintage gear.
Below is my CAP. This is brilliant! A lovely roller-coaster and two beautiful variable capacitors, this unit will match anything from 1 to 30MHz. This is a fantastic AMU for using with a doublet. Below is my S. M Transmatch. I use this with my doublet and my Kenwood TSD.
Initially, I thought this would be rubbish so I sold it to a chap on an auction site. I refunded him and tried it myself. It worked really well so I decided to keep it.
His loss, not mine! The photo below shows the inside of the SEM Tranzmatch. Below is my KW Supermatch. After many years, I finally sold this one. I think it was made by Marconi. The outer coil is 6 inches diameter and the inner is 5 inches diameter. No doubt it would handle quite a few Watts.
Better than medium wave, it was probably used for reactive loading of a kHz maritime antenna. I bought this one, shown below, from a friend recently. It will make a nice preselector for a comms receiver.
I had lots of atu's palstar FC Tokyo hi power. Is very well engineered built to last not like some of to days atu's this thing is bomb proof. Still going strong 20 yrs on. If your looking for one and are lucky to find one buy it. You will not regret it handles full UK power w with ease This A T U has a feel of quality to it slow motion drives marvelous, tuning if effortless and accurate. As an add on to my previous review, I have looked around for similar spec atu's.
If you can find one!!!! I forgot to add that the "D" variants of these atu's mean it has relay switching for on the 2 x coax inputs, and a balanced line. It also has a coaxial input for the balun on the balanced line, and a through position for all inputs. Spike - G0CVL. This was the first piece of HF equipment i bought in ,Leicester rally at granby hall's.
Tunes almost anything,I have had hand capacitance but that was down to me trying to tune something I shouldn't : Only used now when I power my Hunter amp up, takes care of watts easily. Left it neglected in the shed for 7 years, took cover of and sprayed with wd40,gave everything a spin, worked flawlessly.
I remember at the time of purchase thinking"This is really expensive" I'm sure it will outlast me : If you come across one don't hesitate,buy it!!! I have the old CAP. Quite simply, this is the best tuner I've ever used. Tuning up a half size G5RV squashed into a postage stamp garden has until now proven to be a nightmare. The CAP. CO is a neat sized package. Slightly old styling but who cares I want performance and this ATU gives it.
It is a breeze to tune and looks really solidly made. My G5RV is now tuned to using everything from 10 to W. The claimed power ratings look conservative which is good news. The controls are smooth and easy to use. There is no sign of hand capacitance or those little bites that some tuners give.
Time will tell if the relays hold out but if not the basic components are real quality and I will simply hardwire the ATU. This is a bit of kit to keep and get good use out of. More than 12 Months. SWR then scarcely matters on such a high impedance line as losses at low HF will be negligible. Outperforming long runs of coax when tuning up such mismatched antennas.
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