I want to make a feed line for QRP (SOTA, POTA,…) HF bands 40m-10m, CW mode mainly. I’m thinking 7m lenght (23’) is enough for my use, coaxial RG-174 cable. I use EFHW antennas deployed in slope and have fishing rods of 6m and 9m as mastil.
Does it make sense to put a RF choke on the line for this case of use or it isn’t a really advantage for QRP?
If afirmative; do you make it integrated in the feed line or do you prefer as an apart device?
Hi Salva,
I also use an EFD 40 m dipole with a small 2 m tail to eliminate the need to use the coax as part of the radiator. It’s a very much offset feed. The matching uses a galvanically isolated 3 turn primary and an 16 turn secondary. A 100 pF mica capacitance across the primary provides frequency compensation for the secondary distributed capacitance.
The core is type 43 material and I think it’s 30 mm OD. It’s been in use for a while.
I did not include an RF choke because I thought I could add one at the rig if required. It turned out to be unnecessary. So less weight and easier to wind on the winder.
73
Ron
VK3AFW
That is my EFHW antenna for 20m band (note turns 3/21 relation), I tested it with counterpouse but I didn’t note any difference.
That is my EFHW for 40m band (note turns 2/14 relation). It’s good performance in the 20m band too.
I’m using now a 3 meters feed line of coax RG58 (without choke), I consider need more length, but I don’t want to carry more weight.
When operating high power in the shack it makes sense to have an in-line choke to eliminate or minimize unbalanced currents in the feed line from causing RFI. I’ve never had a problem with operating low-power (e.g. <30W SSB / 12W CW) when portable:-
I’m just curious, why do you need 7m of feeder if you are using an end fed? I only ever use end fed antennas but only ever need max 3m of feeder.
Sometimes the best place to deploy the antenna isn’t near of a good place to sit down.
I use several endfeds… here, for example, one with traps for 17, 30 and 60m
In all of them I blocked the coax with a current balun.
It makes sense to have a piece of 0.05 lambda coax cable after the 1:49 unun. The shielding acts like a pigtail.
After 0.05 lambda of the longest band, I use a current balun to block the RF in the direction of TRX. Then I add a piece of coaxial cable so that everything can be connected easily.
73 Armin
I agree, especially in winter. Many’s the time I’ve wanted to put the antenna pole on an unobstructed piece of high ground but wanted to sit below (maybe on the leeward side of some rocks) and out of the wind and rain but had taken my ‘summer’ 2- or 3m feeder rather than a 7- or 10m one needed to do the job.
I didn’t know there is possible and EFHW with traps, I thought there were only dipoles with traps.
Have you any link for learning about to make traps for EFHW antennas?
Thanks Armin!
73 Salva.
I totally agree with you. Moreover, In Spain the scorching heat of the relentless sun in our summer is as dangerous as the wind and cold in winter. So in summer I look for a shady place with a breeze.
It’s exactly the same as for a dipole. You can make a 20m/30m EFHW by having your 20m 1/2wave then a 20m trap then the extra wire to make the length up to a 30m 1/2wave. The trap is low impedance on 30m and high impedance on 20m. The lengths and the trap all affect each other so there is some experimenting/adjusting with the lengths required.
I have a 12.5m-long commercially-made tri-band EFHW for 40/20/10 that uses a trap and works well on air.
This YouTube video might help:
I would strongly advise using a feedline choke on any antenna with traps. I found adjusting trapped antennas to be extremely difficult without a choke. Too many variables otherwise.
… here is a good guide
73 Armin
I’ve found that one like that helps on the higher bands but not really needed on 40/30. You need to try it yourself. JS6TMW
