Monthly Archives: October 2016

End Fed Half Wave Antenna Presentation

Here is a presentation amd a design Spreadsheet I made to our local club on building a End Fed Half Wave Antenna:

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Magnetic Loop Update

I rearranged some PVC fittings to my Magnetic Loop antenna to accommodate the new High Voltage capacitor. Here is what it looks like:

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Remaining improvements are to cover the exposed copper pipe with heat shrink tubing and replace the metal threaded rod with a nylon rod, add a tuning extender and install some band limit nuts to aid in single band tuning. I operated this indoors today but had no luck on 5W QRP. Had to use the amp to make any contacts at 45W.

I also verified the SWR 2:1 points and they measured 48kHz bandwidth which is a definite improvement over the other tuning capacitor which was more in the range of 70kHz. I also verified that the AA5TB spreadsheet was giving the proper tuning capacitor values. To do this I would tune the antenna to a specific frequency, say 14.200 Mhz. The AA5TB spreadsheet indicates a tuning capacitor of 42.42pF minus 8.2pF of loop capacitance for 34.22pF. I removed the capacitor from the loop and measured a capacitance of 38.5pF.

This confims that the spreadsheet gets me the right values for the capacitor which I will now use to finalize the 40m loop design. A quick trip to Home Depot this afternoon yielded the remaining PVC fitting I need for this version.

 

Monitoring Hurricane Matthew Traffic Today

I have been monitoring the Hurricane net on 14.325 today. Also using Broadcastify website to monitor FT Lauderdale Ham repeaters. Our local Echolink node has been configured to monitor traffic on the local nets as well. I am interested to see how traffic is passed around during this storm. God bless everyone in the path of this storm!

HSMM Tests Planned

Another local ham, KB5ZCS, has setup a HSMM node and will be ready to test it this weekend. His QTH is 2.2 miles from mine and he will have the node up about 30 feet. I have dusted off my two nodes and updated the configuration to my new call sign. This should go without saying but don’t forget your password info when setting up your nodes! I did. Turns out there is a procedure for resetting it using “fail-safe” mode. Fortunately that worked!

I have ordered for overnight delivery two 9dBi antennas, a pair of PoE splitters and 50ft of cat 5 coax. The plan on my end is to hand the node up a 20 ft painters pole and see if we can make contact and measure signal strengths. If this works I can mount the node out side permanently on my VHF mast.I am looking to setup a linux server on a virtual machine so there is something to hook up to during the test.

Thinking about my next Antenna Project…

I am thinking of trying to design and build a 20m portable Hexbeam for 20m. I found some fiberglass tent pole repair kits at Academy for $5. These would give me about 9 feet of spreader arm. If I can source some proper sized shock cords I would be able to add additional sections to get the length I need to support a beam. Nice part of these is that they would break down to about 2 foot sections. I am thinking of something that structurally would be a hybrid of the flat spiderbeam design and the inverted umbrella hexbeam design. I plan to keep this to a single band version for now as propagation is continuing to degrade on the higher frequency bands plus this should be a lot simpler to build and test.

Hi-Voltage Capacitor Tweaks

Testing the Hi-voltage capacitor on the small magnetic loop antenna did uncover the need for a few improvements. First up is the tuning rod. The metal threaded rod does seem to couple with my body when I was tuning the loop. I plan to replace it with a nylon threaded rod of the same size (5/16″-18). Tuning the capacitor on the side with the exposed copper outer pipe is a bit risky. I grazed it a few times while trying to tune it while the tuning signal was being transmitted. No burns, but I definitely want to reduce the risk of that.I plan to either add some heat shrink tubing or just wrap some more PE sheet over the exposed sections. Having the capacitor up high does make adjustment a bit awkward. I may have to add an extension rod to facilitate that. I still plan to configure the 40m loop with the captor high and the coupling match low. For the small loop, I can adjust the vertical PVC posts again to accommodate the capacitor in the low position.I’ll replace the PVC cap and eye bolt with another reducer and coupling. Having the capacitor low should also help the balance of this loop on the tripod (not a problem with the larger loop as I plan to hang it).

Testing the Hi-Voltage Capacitor on the Magnetic Loop Antenna

I did some preliminary testing of the Hi-voltage capacitor I completed last week and found some interesting things.Rather than commit the 40m loop design I decided to try and adapt the existing loop antenna I have previously described. To make this work in a configuration similar to what I have in mind with the 40m loop, I installed the capacitor at the top and used a toroid instead of the shielded coax loop for the coupling at the bottom of the loop. To do this is needed to replace the vertical PVC supports to accommodate the configuration. The reducer I used for the 1/2″ pipe on the 40m loop was replaced with a 3/4″ version. This configuration worked well. The capacitor is in the range of being able to tune this loop on 20m. Previous experiments indicated a good match with 5 turns on the FT140-43 toroid. It turned out that 6 turns would give me a perfect match 1:1 SWR at resonance. Here is the SWR plot on 20m.

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TheĀ  bandwidth at the 2:1 points measured at 45kHz. This compares favorably to the original capacitor which was indicating a bandwidth of around 68kHz. This indicates that the Ohmic losses are indeed lower and therefore efficiency should be higher as well.

I did not have enough time this weekend to run all the measurements I had planned but I did operate the antenna indoors at 45W with the FT-817ND and amplifier.The Califonia QSO party was underway and I made numerous contacts in California without difficulty with this loop. The capacitor handled the power without any issues at all!