Roof Mount for BBTD Cable?

[TJPB]

Howdy...first post and newish HAM so bear with me. I'm installing a BBTD antenna based on Bonnie Crystal's design. I know, it's not optimal but I'm in an HOA so have to deal. I will be mounting the wire around the perimeter of the roof at the edge...but on the shingles (asphalt). I would like to use heat cable clips to attach the cable to the shingles but they only come in Aluminum like these. Will they cause an issue/interference being aluminum? Thanks.

 

[prcguy]

Very small pieces of metal otherwise insulated to hold down an antenna wire should have no effect on performance. They would be a very tiny fraction of a wavelength. I would expect more problems with wiring or metal ducting or foil backed insulation in the attic or walls below interfering with the antenna.

I remember when Bonnie first published this info and the antenna has existed in similar form for some time. It would make an interesting project and if the house was all wood with no wiring or plumbing in the attic it should work ok. I have a related antenna, a B&W ACS series, when used with a counterpoise wire is basically the same antenna but on its side. I've had one for many years sitting in the box and last year I finally put it up in the So Cal desert and it worked surprisingly well and didn't need a tuner for 80-10m. Barker & Williamson - ACS broadband end fed vee HF antenna page

 

[popnokick]

The aluminum clips are not likely to influence the antenna. But I do have a few more questions, perhaps best addressed by prcguy or someone who has done EZNEC or other modeling of this antenna. Here goes -
- The original Bonnie Crystal KQ6XA antenna is quite different from the BBTD House Roof Version that is illustrated in this post. In Bonnie's version the shape is "butterfly" with the balun and terminating resistor very close to each other physically. In the house version above, the balun and the terminating resistor are at opposite ends of the house, and not near each other at all. Which raises the next question....
- A "16:1 High-Z Balun" may have been appropriate for the original KQ6XA design, but Is a "16:1 High-Z Balun" the most appropriate balun for this antenna? The "house" version is very different from her original design. Modeling may help determine whether this is the most appropriate balun.
- Something you may want to consider in the design: the end of the antenna that has the 1K ohm terminating resistor. This is similar to a termination on a rhombic where presence of a terminating resistor makes the antenna directional in the direction of the feed point toward the terminated end. Removing the resistor makes the antenna mostly bi-directional along the plane from the feed point to the termination. And a third option with this antenna might be to "complete the circuit" by not using a terminating resistor but instead connecting both of the distant ends directly to each other.. making a loop. A way to accomplish all three possibilities would be a (remote) switch that would either A) put the terminating resistor into the antenna, B) completely disconnect each end with no resistor in place, or C) short the two ends together to make a loop. Controlled from your operating position, you could then select the switch position that gave the best signal.

 

[prcguy]

I think a 16:1 balun and an 800 to 1000 ohm termination is appropriate and its what B&W has been using on similar antennas. It does make the antenna somewhat directional on higher bands but it also smooths out the VSWR.

Closing the loop with no resistor and using an auto tuner at the feed could also work although I made something similar on my "40m apartment" which was square with 32ft along each wall. I had about 130ft of wire under the eaves in a loop fed with an SGC auto tuner and it didn't work very well and I was surprised as others have had good success with similar size horizontal loops.

I reconfigured it with the tuner on one corner of the roof and an inverted V radiating wire going up to an 18ft tall mast in the center of the roof then back down to the opposite corner with a bunch of ground radials fanning out from the tuner under the wire. That worked really well for its size.

The aluminum clips are not likely to influence the antenna. But I do have a few more questions, perhaps best addressed by prcguy or someone who has done EZNEC or other modeling of this antenna. Here goes -
- The original Bonnie Crystal KQ6XA antenna is quite different from the BBTD House Roof Version that is illustrated in this post. In Bonnie's version the shape is "butterfly" with the balun and terminating resistor very close to each other physically. In the house version above, the balun and the terminating resistor are at opposite ends of the house, and not near each other at all. Which raises the next question....
- A "16:1 High-Z Balun" may have been appropriate for the original KQ6XA design, but Is a "16:1 High-Z Balun" the most appropriate balun for this antenna? The "house" version is very different from her original design. Modeling may help determine whether this is the most appropriate balun.
- Something you may want to consider in the design: the end of the antenna that has the 1K ohm terminating resistor. This is similar to a termination on a rhombic where presence of a terminating resistor makes the antenna directional in the direction of the feed point toward the terminated end. Removing the resistor makes the antenna mostly bi-directional along the plane from the feed point to the termination. And a third option with this antenna might be to "complete the circuit" by not using a terminating resistor but instead connecting both of the distant ends directly to each other.. making a loop. A way to accomplish all three possibilities would be a (remote) switch that would either A) put the terminating resistor into the antenna, B) completely disconnect each end with no resistor in place, or C) short the two ends together to make a loop. Controlled from your operating position, you could then select the switch position that gave the best signal.

 

[TJPB]

- Something you may want to consider in the design: the end of the antenna that has the 1K ohm terminating resistor. This is similar to a termination on a rhombic where presence of a terminating resistor makes the antenna directional in the direction of the feed point toward the terminated end. Removing the resistor makes the antenna mostly bi-directional along the plane from the feed point to the termination. And a third option with this antenna might be to "complete the circuit" by not using a terminating resistor but instead connecting both of the distant ends directly to each other.. making a loop. A way to accomplish all three possibilities would be a (remote) switch that would either A) put the terminating resistor into the antenna, B) completely disconnect each end with no resistor in place, or C) short the two ends together to make a loop. Controlled from your operating position, you could then select the switch position that gave the best signal.

Great suggestions. Do you have a link to the type of remote switch you're referring to? Thanks.

 

[popnokick]

Ooops - wrote myself into a corner. Trying to find a suitable 3-position remote-controlled SPDT switch. The Shelly switch I link to here might do the trick... was trying to find something that you could use via Wi-Fi. Shelly makes several different types of Wi-Fi controlled remote switches and I may not have linked to the best one for the job. You certainly can build your own using a low-voltage SPDT relay. Keep in mind that if you use a remote switch you're going to have to figure out how to power it. Could be simple if there is an AC outlet in the attic at the far end of the roofline (I actually have one that way in my attic!) But you may end up running 12VDC to it if no AC outlet. You could power it with a battery but when the battery runs down you'll need to go back into the attic / crawlspace to replace it. If that area is not hard to get to, then you're in luck. In fact, if it's easy to get up there you might want to consider a simple SPDT (On-Off-On) toggle switch and no remote control at all. But it would be best if when you heard a signal you could quickly try all three positions (Open, Shorted, and Resistive Load) without leaving your radio.

Amazon.com

 

[TJPB]

Ooops - wrote myself into a corner. Trying to find a suitable 3-position remote-controlled switch. The Shelly switch I link to here might do the trick... was trying to find something that you could use via Wi-Fi. Shelly makes several different types of Wi-Fi controlled remote switches and I may not have linked to the best one for the job. You certainly can build your own using a low-voltage 3PST relay. Keep in mind that if you use a remote switch you're going to have to figure out how to power it. Could be simple if there is an AC outlet in the attic at the far end of the roofline (I actually have one that way in my attic!) But you may end up running 12VDC to it if no AC outlet. You could power it with a battery but when the battery runs down you'll need to go back into the attic / crawlspace to replace it. If that area is not hard to get to, then you're in luck. In fact, if it's easy to get up there you might want to consider a simple 3PST toggle switch and no remote control at all. But it would be best if when you heard a signal you could quickly try all three positions (Open, Shorted, and Resistive Load) without leaving your radio.

Amazon.com

Makes sense. I think something like this would work as I use similar for WiFi garage opener but I would have to provide AC somehow. There must be a battery version.

4 Channel WiFi Momentary Inching Relay Self-Lock Switch Module,DIY WiFi Garage Door Controller (5-32V) https://a.co/d/9KZp3bh