Hi SWR with End Fed HF Wire 9:1 UNUN

Question

Good Day

I understand every antenna set up is different, so I'm looking for advice on what I could change to alter my findings.

The set up is new including the EFHFW - 20 which was bought off the shelf commercially.

Ive worked all over Europe on it with my low 10w fairly easily but without use of the internal tuner the SWR readings are quite high everywhere.

the Wire is up at 30ft in an inverted V with a bend at the end due to bottom of garden being reached.

The supplying coax from shack to UNUN is around 3 meters / 9ft. The wire is 20m/66ft.

the following are my readings.....

3.500Mhz. 3:5:1

3.700Mhz. 3:1:1

7.000Mhz. 2:8:1

7.100Mhz. 2:8:1

7.200Mhz. 2:8:1

14.000Mhz. 2:8:1

14.100Mhz 2:8:1

14.200Mhz. 2:8:1

14.300Mhz. 2:8:1

28.000Mhz. 3:2:1

28.500Mhz. 3:2:1

29.000Mhz. 3:2:1

29.500Mhz. 3:2:1

I have attached a ground wire to the UNUN earth tag which runs a wire to an earth rod the wire being around 15m long, this appears to make no difference to the SWR, can I assume this wire is also seen as the counterpoise ?

I have tried altering the wire height and angle but found no change in the readings.

Anything else I could try? Someone said to me, ignore it if the tuner fixes it at the radio end, am I over concerning myself, its bugging me I have to admit.

Thanks

Answer 1

Remember an antenna using a 9:1 matcher is meant to use a tuner, whether in your radio or external. The idea is to bring the impedance if a "random wire" down to a value your tuner can handle. The SWR values you show are right where they should be. A lot of internal tuners are limited as to how large of impedance they can handle. If you're down around 3:1, that's pretty decent! You can experiment with different lengths, but even if you get a great match on one band, it will be off on the others. A basic rule of thumb for "random wire" antennas is:

At least a quarter-wave long on the lowest band you want to use, and not a half-wave on any band you want to use.

If you search for "best random wire antenna lengths" there are some good sites that explain everything and give tables of wire lengths for different band combinations.

Have fun!

Answer 2

You can try changing the length of the antenna. Of course be careful as it is far easier to shorten the antenna than it is to lengthen it. In some cases the antenna will be made longer then needed on purpose and you are expected to trim it to get the best SWR for your set up and usage. If this a commercial antenna, you should be able to contact the manufacturer for advice.

If can get access to one try a antenna analyzer to see how the SWR varies with frequencies. There are some relatively inexpensive antenna analyzer on the market today if you want to purchase one. you might also be able to borrow one from another HAM or local club.

I would also check the UNUN and make sure it is OK. On most end fed antennas it is a 49:1 transformer. Look for corrosion or moisture as well as obvious issues like broken wires or bad connections.