Monthly Archives: July 2016

EFHW Matchbox Complete!

Finished the EFHW Matchbox this afternoon. I ended up using a 6:1 turns ratio with 18 turns primary and 3 turns on the secondary. Here is the match through a 1.8K Ohm resistor on 20m:


An SWR of 1.12 with a resistance of 40 Ohms and zero Ohms of Reactance.

Resonance Baby!

Only problem is I can’t tune 40m or 10m. Looks like this setup will only work 30m through 12m bands. Still too much stray capacitance likely.

I marked the cap position for each band and then ran a sweep with the Mini60 Analyzer. This is still with the 1.8K resistor in place. The readings were as follows:


Looks like I’ll be ready to start cutting some wire. I’ll start my tests with 20m which needs a 10m radiator and a 1m counterpoise.I’ll run the 10m radiator as a vertical up the travel mast.

Next test of EFHW Matchbox

I received the type 2 toroids and started to play with them as before by wiring up the parts and testing with the Mini60 Antenna analyzer. This time I tried 24 turns of #22 magnet wire with a 3 turn secondary. I just could not get a match unless I had 5 or 6 turns on the secondary. The frequency was also way off. This didn’t make much sense. So attacking these issues one at a time, I came up with some fixes. First the frequency was off because of the stray capacitance in the leads I was using to hook up things temporarily. I shortened the leads and started getting better results. As for the matching problem, I first put together a spreadsheet that calculated the amount of inductance for various turns on the T92-2 toroid. Then I added some columns that calculated the frequency range of the capacitor I was using. With this data I can find which winding combinations would give me the tuning range I needed. Then I added columns to calculate the turns ratio and the fixed resistor needed to tune to 50 Ohms impedance. I am attaching this spreadsheet but it is not pretty. It tells me that I can ideally use 18 turns of primary with either 2 or 3 turns of secondary for a match. At 2 turns I need a 4k resistor to tune to 50 ohms. With 3 turns I need 1.8K Ohms to tune.This should let me use the match box to tune 40m through 10m. I’ll provide some plots as I get the matchbox built into its case.

EFHW Matchbox

WSPR…How low can I go?

Talking to Cliff, N5CEY, at coffee today about WSPR. He pointed out that there is a power control on the WSPR software that lets me crank down the transmit power. I had been running first at 5W then down to 2W which is the minimum the ICOM 7100 can put out. I have now used this control to bring the power down to 1/2W. I am being heard the afternoon across the US on 20m.Thanks for the tip Cliff!

WSPR with the ICOM 7100

For those folkes trying to run WSPR using an ICOM 7100 you may have found that the WSPR software does not recognize the rig. I am using the WSJT-X software instead which works through HRD to handle the CAT interface. This works very well and also lets me run JT65 and JT9 as well.

WSPR Provides Insight into Band Conditions

I have been running WSPR using my main HF antenna and the IC-7100 the last few days on mainly 40m and 20m. I have noticed that at 2W on 40m I can make contacts to Australia, New Zealand and Japan around dawn on JT65. It is fairly easy to correlate WSPR with JT modes as the S/N thresholds are fairly similar. 20m has been tricky as there have not been many DX openings indicated by WSPR. Most of the openings have been towards Europe in the late evening. What is also clear is that these openings don’t necessarily mean the band is open to other modes even at higher power levels.

The 40m Magnetic Loop Update

Sat down last night and started to work on the 40m Magnetic loop antenna. I have had the parts for this for a while but have not gotten around to building it yet. I hit a snag right off the bat. I had bought a 25ft piece of terminated RG-213 but when I unwound it found that it was closer to 28ft.That put the diameter at closer to 9 feet in diameter rather than 8ft. Of course I have no connectors to shorten the cable handy…sigh. OK, so now if I have to reduce the size of the cable I am thinking a making the loop about 6 feet in diameter. This will give me a bandwidth of 12kHz and an efficiency of 32%. I will need a cap capable of 2kV to mange 25W. Since the antenna is fixed for use at 40m The cap only has to be in the range of 60pF or so. I have ordered the connectors and will shelve this again until I can cut down the coax. This will give me time to think of the cap solution.

And Now for Something Completely Different…


Interpreting WSPR Data for Other Communication Modes

Interpreting WSPR Data for Other Communication Modes is a pretty cool website for using WSPR data for estimating performance on other communication modes. I am interested in coming up with a way to not only estimate the performance of a certain path via SSB but also tie into predicted propagation data. In any case, check out the website and download the Excel spreadsheet to play around with.

Tested EFHW Matchbox components – Fail!

I started to put the EFHW antenna matchbox components together today. I wound 24 turns of insulated #22 wire on a FT140-43 toroid. I measured the inductance and instantly knew I was in trouble…520uH! That was way too much. I will need to order some powdered iron cores to get the inductance down to where my capacitor can tune it. I found a decent source at Alltronics and ordered a variety to try out. Also ordered some #22 magnet wire so that I can try and wind a smaller diameter core.

Update 7/25/2016: Amidon has a bunch of good table and charts useful for designing with toroids. As I indicated above the FT-140-43 toroid is great for a balun but because of its high permeability resulted in over 500uH in inductance… So I have three sizes on order of powered iron Type 2 cores. 24 turns on the T80-2 core results in 3.1uH while the T94-2 results in 4.8uH. Using an LC calculator online my frequency range using the capacitor I have on hand and the T80-2 core is 5Mhz to 29Mhz.  Should let me develop a EFHW antenna for 40m through 1om. Just have to wait for the parts now.

More on the EFHW Antenna

Steve Yates – AA5TB has written a good piece on the care and feeding of the End Fed Half Wave antenna. This is basically a half wave dipole that is fed on one end rather than in the middle. This allows simplification of the antenna mounting as with the random wire end fed antenna. An important difference is that it is resonant on the band it is cut for. Here is a diagram of what I will be building for 20m:


The antenna is cut for 20m half wavelength with a counterpoise that is .05 wavelength long. The match box is composed of a variable capacitor and a toroid transformer with an 1:8 turns ratio. Turns out I had nearly all the parts I needed to build this:


All that is missing is some banana jacks and plus for the wires.I have seen some good things about this antennas performance especially as a vertical. This should work well with the 10m mast. The capacitor is big enough to let me run this at 100W. I’ll try and build this out to test this weekend so stay tuned!