Convenience or Compromise antenna for portable HF?!

 It depends on what one considers as good ops!. When speed matters like in regional emergency comms, NVIS strategy is most beneficial. NVIS antennas for any bands are very low to ground often no higher than quarter wavelength. Dipoles or EFHW hung just few feet above ground get this mode going in shortest possible time.

When one is looking for mid to long range distance comms i.e 500Km + and moves beyond those weak signal modes like FT8, JT65 etc., there comes the need of height, optimized antennas or directivity. This article may be of interest to such Ham Radio enthusiasts who are looking into operating beyond regional comms for non Weak Signal modes and do great. This is based on my experiences of last few years on the field portable ops and subsequent 4NEC2 model based verifications.

First thing first - When we look for portable ops such as POTA and field days, one will come across great amount of content on internet webpages and youtube. Most majority suggest use of End Fed Random wire or Halfwave antennas and some use small loaded verticals. But, look, all were looking at activating the park with 10 contacts or having some outdoor fun during the day. Most of the antennas are low to ground or vertical. Especially EFHW is popular because of convenience of multiband operation. Carefully observing the signal reach patterns of their reports, it is relatively rare that they work 6000 Kilo meter+ distances, on consistent basis. One will get to know US operators working other states around or bordering countries. Like wise in EU, they work each other countries and mostly they are withing  couple of thousand KMs. But in VU where is the active ham population to reach? othenr than during regional NET checkin times on 40m? So, mostly one resorts to FT8 or other similar weak signal mode to increase QSO rate (if that is the objective)

I mostly participate in CW or SSB Contests and objective is optimizing DX QSO rates and score with less weight and hassles. I have worked on hill tops, River estuaries, beach areas etc over last few years and evolved my learning with practically building various antennas such as Dipoles, EFHW, Inverted Vee, Verticals (mono band and multi band fan type), VDA (both mono and multi band), Hexbeam and spiderbeam yagis. I would like to keep VDA and Yagis aside this time and focus on portable popular EFHW and verticals.

Following is the Elevation (Blue) and Azimuth pattern for 40m EFHW in inverted Vee configuration 10meter (quarter wavelength) above average ground. Most of the radiation is straight up and at 10deg angle from ground level, it is around -7dB. 

Second plot is for same 40m EFHW at 20m (half wavelength above ground). Now, we can see the elevation pattern is shaping up with -0.13dB gain at 10deg angle. These plots will be same for standard inverted Vee centerfed dipole at fundamental resonant frequency.

But this pattern distorts for higher resonances such as 20m, 15m and 10m bands with additional azimuth wing patterns and lowering elevation angles. Based on the situation they may be taken as advantage or can be disadvantageous.

Advantages of EFHW are many--

a) Requires feedpoint at lower height i.e less coax

b) no more heavy duty pole or support required at center point

c) resonates at multiple harmonic frequencies

If EFHW is similar to dipole, why not just use it all the time?

What the modeling misses is actual transformation loss and RFI. EFHW requires carefully built (often shown as easy to build) 49:1 or 64:1 transformer at feedpoint. And in mono band version of  EFHW, one can construct simple feedline stub to gain the advantage (example JPole) of much lower loss. When operating portable, many compromises made in the name of QRP starting with lossy Coax, fact of RFI pickup is not noticed etc. These can be excuses only for highly tactical and worst case situation, but attentive ham should be careful more than QRO ops as inefficiencies adds up. For example: Let us consider 10W output from Transceiver connected to EFHW with RG58 of 10m length. Let us assume with 1.2:1 SWR antenna. This delivers approximately 9Watts to feed point. A transformer loss of 20% on this 9Watts brings down another 1.8Watts i.e power delivered to antenna will now be 7.2Watts. So, even before one says antenna is efficient or no, we have 28% reduced power already delivered due to convenience we wanted. OK, now most of the time I have been told these losses are negligible and no one will differentiate on the other side etc. I agree to some extent, but on the edge condition, these negligence matter a lot and which could be fixed easily.

Adding a coax such as RG213 or LMR 400 and feeding antenna directly such as dipole ( or vertical) without transformer is next step up bringing the losses to less than 10% (efficiency goal in my case). I made first SSB, CW DX QSOs with simple fan inverted Vee only. High apex works always! Verticals are though directly fed, will pose roadblocks in to efficiency journey if not given attention to its ground system. 

I have both QRP and QRO dual core EFHW transformers in my portable kit as fallback. But do I prefer them over dipole?. No. because there is one more reason I have not mentioned earlier with importance, i.e RFI in the Coax line leading up to shack. Unbalance nature of the random wire and EFHW, forces RF on outer shield of coax in both transmit and receive. While transmit RFI is obviously experienced in causing interference to other nearby transceivers, interconnect wires, and if QRO, tingling sensation while speaking to handmic/keying and distorted audio etc. Receive issue is even worst as it picks up local electrical noises and raises the noise floor. To minise RFI we can add counterpoise wires or choke on the line after few meters from transformer etc. But the point is convenience comes at price.

So what other options?. Ofcourse, there is dipole when 1/2 wave height could be established or verticals good radial system. Following are two plots, one on the left is ideal vertical(needs atleast 16 radials or more) on average ground and on the right side with single tuned elevated radial. While two or more elevated radials provide balanced omni pattern, single radial provides some directivity in the direction of the radial. This type of system was practically tested at one of our early field experiments for 80m band which can be found at Blog post link

Here is overlap of two elevation patterns. My experiences showed that when no other antennas are close proximity, having elevated tuned verticals are advantages as it becomes easy for field portable to achieve better efficiency than few ground level radials.

Also, if we are at coast verticals even work much better at 5 to 15 degree elevation angles for great DX. But dot not get overwelmed with EFHW stung vertically to think it will perform same for all the harmonic bands. Just like EFHW in inverted Vee or horizontal position, distorting patterns on harmonic frequencies, vertical also forms higher angle signals which will not be useful in long range.

So while we chose the antenna at hand as better than none, when there is choice, make optimal use of them for the situation, location and purpose we intend to. Afterall, Ham radio is a learning and advancement hobby, just try these and prove!

Have fun

Kiran VU2XE