this really shines some light on balanced feed line matching. still using a Johnson Matchbox on my ladder-line fed doublet with good results! she worked for me when i was a kid in 1959 and it's still doing a decent job. Its ironic (to me anyway) that in this day and age it's rather difficult to find a "balanced line" antenna matcher (tuner) that does as good a job as this one did back in the day :)
I would complete your comment by adding "when used with open wire line feeding an antenna that is a half wavelength long or more at the lowest frequency". The matchbox is terrible compared to a high pass Tee network when matching other than the range it was designed for. Try to load your 40m dipole on 80m and unless you have chosen the "correct" length of transmission line the Matchbox will not match. This is fun stuff and glad you liked the video. Larry, W0QE
Hi Larry, Thanks for this and all the excellent videos that you have produced. They are an incredibly valuable resource that makes the world a better place through your generously shared knowledge and know-how. I can confirm that the common 15 and 10mtr taps on the rear coil are indeed stock standard on the 1kW Matchbox while the front coil retains separate 15 and 10mtr taps.This is the case on my complete unmodified unit, and also on a coil/switch assembly that I purchased separately as a part only on eBay. It seemed incongruent to me that a balanced antenna matching device would have an asymmetrical coil assembly on one band, but your demonstration of the SimSmith modelling sweeps makes me think that designers did this to deliberately shift the 15mtr "matching hole" around to a less troublesome Smith Chart location at typical Amateur dipole lengths.
Peter, We will most likely never know exactly what the designers intended but I'm pretty sure that if a program like SimSmith and computers had been available to them the result would have been different. Maybe not too much different or maybe a lot. We can only venture a guess. Larry, W0QE
Great explanation, thanks. 👍 (I would have asked SimSmith creator AE6TY to place the generator/input on the left and the output/load on the right -- as per the universal convention for schematics.)
James, Historically the Smith Chart was used to calculate an impedance that the generator would see so the order of calculations was from the load towards the generator which logically put the generator on the right. SimSmith does so much more than just calculate impedances which might mean that sometimes the generator would be more suited on the left and other times on the right. Fortunately you can have it both ways. Click on view, backwards circuit to put the generator on the left. Larry, W0QE
Good work here.These preform very poorly with open wire line due to their very narrow range with a balanced load.Used it with a half wave on 160 and full wave on 160 and most of the time I could not tune the the reactance.On some bands I had to cut the feed line an odd multiple of a quarter wave to keep the voltage out of the shack, this however has nothing to do with the tuner.I had a few hundred feet of feed line hooked to these antennas about 125 feet at the apex.The matchbox has a very narrow tuning range with a balanced load I believe 1200 ohms was the top number.
this really shines some light on balanced feed line matching. still using a Johnson Matchbox on my ladder-line fed doublet with good results! she worked for me when i was a kid in 1959 and it's still doing a decent job. Its ironic (to me anyway) that in this day and age it's rather difficult to find a "balanced line" antenna matcher (tuner) that does as good a job as this one did back in the day :)
I would complete your comment by adding "when used with open wire line feeding an antenna that is a half wavelength long or more at the lowest frequency". The matchbox is terrible compared to a high pass Tee network when matching other than the range it was designed for. Try to load your 40m dipole on 80m and unless you have chosen the "correct" length of transmission line the Matchbox will not match. This is fun stuff and glad you liked the video.
Larry, W0QE
Hi Larry,
Thanks for this and all the excellent videos that you have produced. They are an incredibly valuable resource that makes the world a better place through your generously shared knowledge and know-how. I can confirm that the common 15 and 10mtr taps on the rear coil are indeed stock standard on the 1kW Matchbox while the front coil retains separate 15 and 10mtr taps.This is the case on my complete unmodified unit, and also on a coil/switch assembly that I purchased separately as a part only on eBay. It seemed incongruent to me that a balanced antenna matching device would have an asymmetrical coil assembly on one band, but your demonstration of the SimSmith modelling sweeps makes me think that designers did this to deliberately shift the 15mtr "matching hole" around to a less troublesome Smith Chart location at typical Amateur dipole lengths.
Peter,
We will most likely never know exactly what the designers intended but I'm pretty sure that if a program like SimSmith and computers had been available to them the result would have been different. Maybe not too much different or maybe a lot. We can only venture a guess.
Larry, W0QE
Always wanted to own one👍💯
Good video, Larry. I think there will be a lot of interest on this one. W0IVJ
I had the 250 watt one. Thier up thier in price god i still want one👍💯
I believe they started production in 1953 - I have an early model with a manual dated 1953.
Bob.
Thanks for the info.
Larry, W0QE
Enjoyed this, especially since I own two of these Matchboxes. Nice analysis Larry. Dennis, N0SP
Dennis,
Glad you enjoyed the video and nice to hear from you.
Larry
Great explanation, thanks. 👍
(I would have asked SimSmith creator AE6TY to place the generator/input on the left and the output/load on the right -- as per the universal convention for schematics.)
James,
Historically the Smith Chart was used to calculate an impedance that the generator would see so the order of calculations was from the load towards the generator which logically put the generator on the right. SimSmith does so much more than just calculate impedances which might mean that sometimes the generator would be more suited on the left and other times on the right. Fortunately you can have it both ways. Click on view, backwards circuit to put the generator on the left.
Larry, W0QE
Good work here.These preform very poorly with open wire line due to their very narrow range with a balanced load.Used it with a half wave on 160 and full wave on 160 and most of the time I could not tune the the reactance.On some bands I had to cut the feed line an odd multiple of a quarter wave to keep the voltage out of the shack, this however has nothing to do with the tuner.I had a few hundred feet of feed line hooked to these antennas about 125 feet at the apex.The matchbox has a very narrow tuning range with a balanced load I believe 1200 ohms was the top number.