W4OP Loop FAQ
Do you have plans to build in functionality to have the Loop rotate remotely?
Regardless of what you might read on the internet, STL’s are omnidirectional for all useful ionospheric propagation angles. At 0 degrees they have a null that might be useful for reducing a local noise source. As the elevation angle increases, the depth of that null disappears rapidly. At low angles, an STL is vertically polarized and at high angles it is horizontally polarized.
Should I use my rig’s tuner with the W4OP Loop?
Absolutely NOT! The Loop must be tuned via its resonating capacitor. However, do not confuse the fact that the antenna is tunable and it tunes all across the band. If you rely on the rig’s tuner it will not work at all. If the main loop is not resonated, then the coupling loop cannot transfer the RF to the large loop.
How does tuning affect SWR?
Remember, your rig’s tuner does NOT change the SWR at all. SWR is defined as the mismatch between the antenna and its transmission line. All your tuner does is make the rig happy. It does not change the SWR. The result is this for say 50’ of RG-174 on 28.1MHz with a 4:1 SWR
- The loop (any loop) will not radiate if not resonated. But for the following let’s assume we are talking about a dipole whose SWR is 4:1
- The 1:1 (matched) loss of 50’ of RG-174 at 28MHz is 1.8dB
- The penalty for the 4:1 SWR is an additional 1.2dB
- So 3dB or half your power is wasted in heating up the coax.
So if you were running 10W, less than 5W makes it to the antenna- which because it is not tuned will reflect all of the 5W back to the rig in simplistic terms
Do you plan to have an auto-rotator for your loop?
No as there is little to no benefit. The short answer is that the nulls of an STL exist at the horizon ( 0 degrees elevation). So an STL can be used to reduce a local noise source
and nulls exist for signals arriving at the horizon ( ground wave). But for the vast majority of ionospherically reflected signals an STL displays very little if any directionality. At very low elevation angles, the loop’s polarity is primarily vertical. As the elevation angle increases, horizontal polarity increases, filling in the vertical polarity nulls. At an angle as
low as 30 degrees elevation, the nulls can be as shallow as 5dB. Given typical HF fading of 20dB, finding the direction of maximum signal would be difficult indeed. Remember that the polarity of ionospherically reflected signals constantly changes. A signal transmitted from a vertical antenna at station A, may arrive at any polarity between vertical and horizontal and continually changes with time. This why a single STL is not used for direction finding at HF. More complex arrays like a loop that is electronically combined with a sensing vertical or an Adcock array are often used. Here is a link to an explanation of the above:
Can the EndFedz be used on bands other than the design band?
In general, no. These antennas are monoband. Using them with a tuner for other bands wil guarantee that the coaxial shield will become part of the radiating structure and may harm the matchbox.What is the radiation pattern of the EndFedz?
Characteristics are identical to a center fed dipole.
How can I extend the bandwidth of the EF-10/20/40 on 40M?
In designing the EF 10/20/40 we intended to make an antenna that would be portable and easily deployable. As a result, we use a choke to isolate the first 33′ from the remainder of the antenna. The choke, then, acts like an inductor shortening the 40M half wave from 66′ to 40′. If space permits, a 66′ wire may be attached to the matchbox; yielding wider 40M BW, and slightly more 40M gain. On 20M, the antenna will appear as a full wavelength. A 1 wavelength antenna has a null at the horizon, and thus may not be suitable for DX work if the antenna is deployed as a vertical. Deployment as a sloper or horizontal overcomes this problem.
What limits the power on the EF-10/20/40?
Can I use the EF-10/20/40 matchbox on other bands?
Yes, remove the factory supplied radiator and substitute a radiator whose length is 1/2 wavelength long on the desired band – from 60M up to 10M.
Can I use my monoband EndFedz matchbox on a different band by replacing the wire?
No. Each matchbox (with the exception of the EF-10/20/40) is different and band specific.
Do the EndFedz require a ground?
The simple answer is no. With over 4,000 antennas in the field, we know of one instance where RF was “in the shack.” This occurred with the antenna directly over the operating position. Moving the antenna solved the problem. If you do ground the antenna at the matchbox, you will likely see no change in VSWR or resonant frequency. The only conditions where we were able to measure significant RF on the outer coaxial shield occurred when:
- The coaxial length was an odd multiple of va wavelength AND
- The rig was grounded.
In this instance we measured current -7dB down from the peak antenna current. Changing the coaxial feedline length OR removing the ground significantly reduced the currents.
Do EndFedz require a tuner?
No tuner is required, nor should one be used. Take the short time required to tune the antenna.
Can I add additional 1/2 wave wires to the EF-10/20/40 matchbox and work multibands?
No. Unlike a center (current) fed dipole in which a fan arrangement of wires allows for multiband operation, the wires on an endfed (voltage) must appear in series- either through a trap/choke arrangement or harmonically related frequencies (eg. 7/14/21/28 MHz).
Can I combine coaxial cables from different EndFedz for a single downlead?
No. You will need a remote switchbox or separate feedlines.
What is the black grease-like substance on the 10-32 threads?
It is a commercial product intended to prevent oxidation between dissimilar metals in the electrical industry. We are using No-Gard® but the same product can be found under other trade names. One interesting aspect of voltage fed antennas is that corrosion at the matchbox will have essentially no effect on performance. So our use at the matchbox is simply to prevent the stainless hardware from galling. The only low impedance connection on our antennas is at the 20M choke. On 40M, the end of the choke nearest the matchbox is a high current (low impedance point). So, on that 10-32 stud, the No-Gard® serves the dual purpose of preventing corrosion and lubrication.
What is the best grounding arrangement for the EF-SWL?
Unfortunately, there is no one answer. That is why we have provided separate grounds on the matchbox. Lug 2 is the ground end of the antenna side of the transformer while #1 is ground for the coaxial shield. Depending on the source of noise, it may be advantageous to:
- Leave the factory shorting strap in place and attach either lug to a suitable RF ground at the antenna.
- Remove the strap and ground only lug 1 at the antenna site. Then, the receiver may be grounded or left ungrounded- whichever results in lower noise.