Maybe a little off topic: I recently corresponded with Owen, VK1OD and Steve, G3TXQ. I have been very busy this summer with a bit of traveling and a long hour daily summer work schedule to get off on Fridays and have not had a chance to resume the discussions with these gentlemen and recently along with Charley, K1DNR. Common mode impedance has been the main topic along with balance. I am trying to arrive at the best configuration for general use for my personal information and to help with a specific case with a local op. I ran tests on a few transmatchs. During this process I have finally defined a "voltage" balun and a "current" balun for my purposes. As far as I am concerned, the definitions are same for a balanced transmatch or a stand-alone balun. A current balun/balanced transmatch has high common mode impedance. In the case of the current-balanced output type of transmatch the high common mode impedance means the isolation from the chassis also must be high. If the isolation isn't high enough you throw out the benefit of having high common mode impedance. If the common mode impedpance is high and mostly resistive in nature (low Q) and the isolation from the chassis is high (low capacitance from the output terminals to the chassis) there is automatically good output balance and good disruption of common mode current (breaking of the common mode RF path). On the other hand, using the old Johnson Matchbox as example, there is the Voltage type transmatch where the common mode Z is very low but yet the output terminal balance is very good (good mechanical construction and symetry). What I have arrived at in my mind and the point I am trying to convey is that the definition of a "current" type and a "voltage" type balun or balanced transmatch is nailed down simply by measuring the common mode Z. In addition, one should design for one type or the other. If a transmatch or a balun is designed with mixed features (a device designed to be current type that has low common mode Z or poor isolation from the chassis for example), there will be issues to contend with for the general application. In other words, you'll have good results at one op's home but poor results at another, etc.. I hope the point I am trying to convey is at least something to consider.
The other benefit of high common mode impedance, good balance and high isolation is reduced receive noise. 73, Pete.
That's just silly! Everyone knows cat litter works better!!
Originally Posted by WA8KJP
I have to disagree. It seems current baluns are often said to work better than voltage baluns on OCF antenna's by the "experts" but yet no factual data is ever provided for any side by side comparative analysis. So how do you explain your statement in this case exactly?
Originally Posted by K1DNR
Pete, common Z doesn't explain anything. Even a dummy load has common Z for that matter. I fail to see any relationship, maybe I am missing your point or something.
Last edited by KC8VWM; 08-13-2012 at 04:26 AM.
73 de Charles - KC8VWM
North American QRP CW Club #3159, SKCC# 5752
G'day all, after my initial forum barrage this morning (our time), I decided to repeat earlier balun tests (done many times before), and I'd forgotten about the 'hybrid balun' which is a voltage 4:1 balun series combined with a 1:1 current mode balun on it's output, and I have to admit its noise pick up is several S points less than a simple 4:1 voltage balun, an impressive result.
Lower noise pick up is always worthwhile. So I'll concede that maybe current mode baluns are better (in some respects anyway)! Regards, Felix vk4fuq.
Can you be specific? If the article is flawed, I need to know and do something about correcting it.
Originally Posted by VK4FUQ
G'day mate, well it appeared to only work as intended on 20 m. On both 40 m and 80 m I found that I needed to use considerably greater amounts of inductance on my Dentron T-match ATU than with the usual 4:1 ATU balun arrangement to get a good low SWR match through the ATU.
Additionally on 80 m when tuning up, my transceiver (an Icom IC-718) would burst into mysterious oscillation on occasions when using a 1:1 choke balun.
All three antennas are fed with random lengths of 300 ohm balanced feedline as needed for the distance to the antenna feedpoint (more than 30 feet, as the minimum). Regards, Felix vk4fuq.
Last edited by VK4FUQ; 08-13-2012 at 10:46 AM.
Don't stop questioning the status quo. Sometimes it can turn out to be wrong. If people didn't challenged accepted facts, we'd still think the sun revolved around the earth and that the earth was flat.
G'day mate, no I never stop 'questioning', that's all part of my Aspergers nature (sometimes unfortunately)! Regards, Felix vk4fuq.
You'd expect the tuner settings to be different, because the load impedances are different with the two baluns. Why do you think that is a problem?
Originally Posted by VK4FUQ
Was it stable once tune-up was complete?
Originally Posted by VK4FUQ
In Post#25 you reported a drop in noise level of "several S points" when you followed the 4:1 voltage balun with a 1:1 current balun; that should tell you a lot about which balun is better at maintaining current balance!
In earlier Posts you said your primary concern was balun loss, and you quoted a loss for a current balun of 0.6dB-0.8dB. Do you think that sort of loss explains you original statement that "signal reports were much better than they are now using current mode baluns"?
By the way, I'd be embarrassed to admit I'd built an HF current balun with that level of loss!
If you question the status quo without trying to minimize influences OUTSIDE of what you're wondering about, you won't learn much. Questions need to be focused and their answers hinge on doing the best you can to make sure the investigation is capable of giving you the answer.
Originally Posted by M0GVZ
Does that really happen when testing a single antenna component against the memory of signal reports past?
Skepticism is important, especially in an environment where information is passed around as sound bites like "current baluns are better than voltage baluns." But it's important to go beyond doubting the "common wisdom" because of some observation. It's crucial to find out WHY your observation happened, and whether it really corresponds to your guess for why it happened. Established facts are effectively challenged by reproducible data. They are challenged by saying "here is what I thought happened. It was weird and counter to what I thought would happen, so here's how I went about testing it... try out this test or a similar one and see if you find the same thing."
Reporting ONLY the observation is not bad; observations on their own and a guess for why they happened can sometimes spark those with better tools to do experiments confirming or refuting the link between the hypothesis and the observation. But observations that aren't rooted in something that ANYONE else can reproduce don't actually challenge the status quo effectively, because it's just not very convincing, especially to other true skeptics.
Originally Posted by VK4FUQ
How many years are you talking about?
In your years of data collection, have you considered increasingly restricted antennas? Have you considered a bad economy and employment/retirement insecurity making a $4000 tower+beam project a bad bet? Have you considered the rising prevalence of tall, untuned verticals that have bad high band patterns and random coax losses in the 1-20dB range depending on band? Have you considered whether the consumer-gadgetry noise floor has continued to rise? Have you considered the expectations of new hams in distant locales who may be using really terrible antennas and thinking it's "normal" to get low signal reports? Have you considered those who come from a certain radio enthusiast culture that puts too much focus on amplifiers and output power, so they expect low reports at 100W? What about the ones who think it's "normal" to never hear Australia because they've never used an antenna higher than the top of their back yard privacy fence?
There are certainly situations in which a poorly chosen "current balun" could strongly reduce signals, like trying to choke an off-center fed antenna with a choke of insufficient impedance. But in a lot of those situations the balun would suffer heat damage in many installations. There are all kinds of differences between a given installation that uses different kinds of baluns because you change a LOT of the current and field structure by swapping baluns. But there are also a lot of other factors that come into play, and I can't imagine that the influence of a current balun vs. a voltage balun could stand out among the rest, especially because in many situations there would be no way for a current balun to reduce the signal even a few tenths of a dB.