2
$\begingroup$

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

$\endgroup$
1
  • $\begingroup$ Hello Simon, and welcome to this site! I just Googled "EFHFW - 20" and found nothing. Could you please edit your question with a link to your antenna? $\endgroup$ Oct 27, 2022 at 17:30

2 Answers 2

1
$\begingroup$

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!

$\endgroup$
1
  • $\begingroup$ R Pau is correct, Simon Hefford. but consider that your, description of the antenna is not correct for most bands you list, and the one it is a halfwave for, 40M (7.1MHz), you should be using a much higher ratio transformer for, like 49/64:1; you are in the ballpark and you just need to do a little impedance and reactance tuning with a tuner. An interesting chart would be the impedance and reactance results you get in each band if you get yourself an inexpensive NanoVNA. Not withstanding that this is a compromise setup, and you are losing a lot of power, you do need to get your VSWR down. $\endgroup$ Apr 6, 2023 at 19:15
0
$\begingroup$

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.

$\endgroup$

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .