Category Archives: Antenna Stuff

Mar 22

Laurie’s new HT

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Laurie, KB3SIK had seen the Kenwood TH-F6A during our most recent Project Lifesaver exercise and really liked the size of the rig compared to her TH-D7AG that I got her for Christmas. It wasn’t long before the D7 was on ebay and the F6A was enroute from Ham Radio Outlet. I was also looking into the radio as well since I’m in need of a receiver that can do 216mhz on sideband. The Project Lifesaver beacons output a minimal amount of power around the 216-217mhz band and their signature can be heard in sideband mode. It is possible to hear it on AM although what your hearing is a lack of signal, or drop of static when the beacon bursts. The usage of AM almost requires you to be within a 1/4 mile of the beacon’s location, even with a 6 element yagi.

Well it arrived today and I think I’m going to stick with my new D72A. The F6A is a little too small for me, although the fact that it can receive AM/FM/SSB and CW is a real help. Hopefully she’ll let me borrow it for our future outings. Check it out!
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Mar 21

Antenna switch project

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In the weeks leading up to the ARRL DX Phone contest this year, Eric, WG3J and I did some extensive antenna planning at his QTH in Maryland in preparation for the upcoming contest. One of this biggest concerns was the amount of coax coming into the station. During a contest last year, we encountered a ton of RF affecting computers and audio causing an RF burn or two. Fun times.

How to resolve this? Reduce your coax run length and quantity by using antenna switches.

I reviewed a number of designs online and ended up designing my own, 2 position antenna switch which injects 12VDC onto the coax, so we didn’t require additional long lengths of control wire which could end up resonating RF.
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For the next 3 weeks part of my station would be turned into an assembly line, etching circuit boards, fabricating cases, etc.

A week before the contest, Eric and I put the switches through their paces by dumping 2.5kW at 100% duty cycle for about 10-20 seconds. This would help us assure that they would hold up to the contest pace.

I ended up building five switches, 2 rated at 10kW and 3 rated at 5kW. I’m happy to report success with the design with no smoke emissions. One thing we did find was a high SWR at 15m and above, which I believe I have a fix, that needs future testing.

Mar 21

N3QO: 160m mobile

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Greetings from a fairly long blog posting hiatus. A few cool things have been in works around N3QO, on or near the top of the list is going 160m mobile. That’s right, 160m.

Barry, KU3X and I discussed the capabilities of 160m mobile in the summer. He had a successful coil design for his mast and whip combination with good signal reports into our nightly 160m net on 1900khz.

Fast forward to this last weekend where I acquired a quick disconnect (QDC) for my screwdriver antenna and a spool of 16ga enameled wire from the LVARC table, all at the Cherryville Hamfest in NJ. Now that I had the wire and QDC, what better time to build the coil and attempt to go mobile on 160m with my High Sierra HS-1500MKII screwdriver antenna.

At first I just winged it, and used a 3 inch PVC as the coil form, with 7 inches of exposed PVC between the end caps. I ended up with a 100 turn inductor that I would later discover calculates to 390uH of inductance. After reviewing someone elses blog about an inductor for this purpose, I ended up being about 110uH of too much inductance. After a little experimenting, I removed about 20 turns and tested again. I had found my resonance was around 5850khz.

This is where I started utilizing my MFJ-259B analyzer beyond the typical SWR readings. I had found a relationship to inductance at the resonant frequency to be 0uH, and 25uH at 1900khz, our target frequency.

With this new information I removed another 5 turns and now found I was around 4:1 SWR at 1900khz with resonance still up and around 5Mhz. It was then I remembered that the 40m shunt coil at the base of my antenna was still in the circuit. Once I removed the matching coil, SWR came down to 2:1. All I had to do now was to raise or lower to the desired resonance, 1:1 at 1900khz.

After I had the test case completed successfully, I re-evaluated the connection points, I decided to drill an entry point to wire the coil from inside the coil, which makes for a cleaner appearance. I also decided to anchor the caps with 4 screws each and not sealing the form in the event of internal coil failure. Because of this, a drain hole exists at the base, only millimeters away from the bottom connection point.
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Here are the specs on the coil:
Length not including quick disconnects: 11 inches
Turns: 75 (i think)
Calculated Inductance: estimated 270 uH
Tuning: Allows tuning down to 1815khz at 1:1 with screwdriver fully extended.

On air reports were surprisingly good. I have an Icom 706Mk2 running 100w.
I was S9+20 into Pittsville, MD, S7 into Western PA all from the Pottstown, PA area. This is typical of what I expected, but never that great of a signal.

I’m planning on building another coil with a few less turns with hopes of bringing resonance down to 1800khz even. Then this will truly be a 160m coil.

–jeff
N3QO