Tuesday, November 24, 2020

Palstar AT1KM 1:4 ruthroff balun - a wrong choice?

 I own a discontinued Palstar AT1KM. I consider Palstar as one of the best antennatuner builders. The tuners are expensive but quality is very good. It works fine, actually I never had troubles with it and tuning is very easy. However, in the past even antennatuner builders had it wrong. 

A while ago a began to read about baluns and what they do. I read several tests with baluns at the output of a unbalanced tuner since I was unshure if I should use a 1:4 or a 1:1 balun behind my CG3000 autotuner to feed my vertical. I did some experiments myself and continued to read all about it. Now finally I read a article in a Dutch amateurradio magazine called Razzies about baluns that was a real eye opener. It contained a test with a voltage, current and no balun with both coax and open line. The winner was clearly the current balun in all cases. 

Now, I was thinking....

On the back of a Palstar tuner the balun instructions
Inside the AT1KM is a 1:4 ruthroff voltage balun for balanced output, I guess it was kind of a standard about 10-15 years ago. My MFJ948 also had a 1:4 voltage balun inside. But with the knowledge of today it seems it is not the right choice to make. I was curious if Palstar is still using a ruthroff balun inside their tuner. If I look at the AT-500 the specs tell me they are using a 1:4 current balun, though if I look on the photo it looks like the ruthroff balun in my AT1KM. Two other tuners they make don't have baluns inside anymore. Baluns are now available in a non conductive housing which should be connected with the shortest possible coax to the tuner. the reason: baluns mounted against a metal chassis are subjected to mutual capacitance, which may also disturb the balance.  It is simply better to mount them externally in a plastic box (Owen Duffy, VK1OD). The Palstar engineers listened well...

Actually the same Owen Duffy came to a conclusion: "A unbalanced T match followed by a 1:1 Guanella (current) balun in an external non conductive enclosure and having high choking impedance, very short coax connection to the ATU, and high voltage withstand is capable of excellent performance in a ‘balanced ATU’ role for general purpose HF application."

...Exceptions are the heavier Palstar AT4K and AT5K manual tuners which have a 1:1 balun at the input and mounted inside the tuner housing but not against the housing. At first I though, why not? What difference would it make. This is what W8JI tells about it: "Any article that claims placing a current balun at an unbalanced tuner input helps balance, or generally helps the balun work better, unfortunately is mistaken. Moving the current or choke balun to the input of an unbalanced network makes balance much worse on higher bands, and does not help lower bands".
It is unclear to me why Palstar engineers did choose such a configuration with high power manual tuners anyway? The risk of destroying a 1:1 balun with high power is very high anyway.

So, how to make your T-match tuner work better? Is it that simple? Yes it is....don't replace those 1:4 ruthroff baluns in your old tuner. Let them be. Just make the best current balun you can, place them in a plastic box and connect them with a short as possible coax to your tuner to feed a open line to your antenna. Does it really help? Well, it depends how you antenna is configured I guess. But if you want to feed a open line to you antenna it is just as easy as connecting a good quality 1:1 current balun between the tuner and the open line. You don't have to buy a expensive balanced tuner or a tuner that has a balun inside.

Will we have different thoughts about this subject in the future? 20 years ago it was common to place a 1:4 balun inside the housing of a antenna tuner, most of us didn't have the equipment to verify if this was working right. With the decreasing prices of specialized measuring equipment confirming that your gear is working well is in everyones reach.

Sunday, November 22, 2020

Friese 11 steden contest 2020

 This is a dutch language contest, however open for international traffic. But since the content is only interesting for the dutch I'll write it in dutch for archive purposes.

Event: Friese 11 steden contest 2020 
Section: Buiten regio 14
Logger: N1MM+ 
Station: Icom IC-7300 100W
Antenna: Inverted-V @ 12m

Foto rechts: Vanuit de radioshack. Dat grote gebouw op de achtergrond is de originele "rode" school. Er was een station die er aan twijfelde. Uiteraard word het gebouw niet meer als school gebruikt. Overigens is het maar de vraag of de naam "Roodeschool" van deze school afstamt.

Voor mij is dit de leukste nederlandstalige contest van het jaar. Het speelt zich alleen af op de 80m band en dus de bereikbaarheid van Nederland is meestal prima.

Het leukst is natuurlijk het speuren naar de 12 steden/dorpen die mee tellen als multiplier. Of dat lukt is altijd de vraag. Sommige multipliers zijn maar een korte tijd aanwezig. Als je ze mist heb je pech. En dat had ik deze keer. Ondanks dat alle 12 multipliers aanwezig waren heb ik Harlingen wel gehoord maar niet kunnen werken en Bolsward helemaal niet gehoord. Nou heb ik wel heel relaxed mee gedaan en hier en daar een praatje gemaakt, want daar is deze contest ook een beetje voor bedoeld. Maar misschien was ik wel een beetje te relaxed. Denk dat de beste strategie is om elke 15 minuten ook even de band over te draaien om multipliers te zoeken. Ik heb dat wel een paar keer gedaan maar ook best veel CQ geroepen. Dus maar 10 multipliers....nou ja het geeft niet. Ik heb een hoop plezier gehad en een hoop bekenden gehoord en gewerkt. De vreemdste plaatsnaam voor mij was toch wel de QTH van PE0JXA/P die bij het haventje van Oude Zeug stond. Ik hoorde een aantal andere stations ook worstelen met deze plaatsnaam en had er zelf ook nog nooit van gehoord. Tja, dat zijn leuke dingen die gebeuren vind ik en je leert ook nog wat. Even opzoeken, waar ligt dit plaatsje:

Als ik zelf in die situatie zou staan had ik toch gekozen voor de plaatsnaam Kreileroord. Maar goed, bijzonder is het wel.

Het was alles bij elkaar weer een bijzonder leuke en gezellige contest. Ik bedank de organisatie, want die krijgen het toch elk jaar weer voor elkaar. Tot volgend jaar!

Hierbij nog een korte video opname. Met o.a. PA2LO, PA3MM, PA7MM, PA0Q en PA3JD. Ik had nog meer op willen nemen maar achteraf waren het alleen foto's en geen video.

Friday, November 20, 2020

RF antenna current meter

For future experiments and the one done recently I really need a antenna current meter. Best is something that shows the balance as well since that is one of the features a S-match offers. Another thing you can measure of course is the RF current which should be as high as possible. That way it's possibible to compare antennatuners on open line.

PA0FRI  has a good design on his site. Components are not really critical as long as they are the same for both lines. 

As a real amateur experimenter I first look around in my scrap box for parts. It took a while but I found everything except the plastic boxes to build everything in. Some soldering and fitting....this is the result:

Frits does use T80-2 torroids with 25 windings. I found two pre winded ones in my scrapbox, 23 windings on a unknown torroid. The big 2W resistors should be 50 Ohm, other designs show 100 Ohm. I found two indentical 82 Ohm resistors that will do the task. For meters I found a nice AKAI VU meter combo I salvaged from a AKAI cassette player. It took me some research to find out these are microA meters, just what I needed.

Because I didn't know if it would work well I decided I would not build the meters in a box yet. 

Basically this is bare system. It actually works better as expected so I'll continue to make it look nice in some time.

Now, I was very curious about my antenna system (2x 20m inverted-V "doublet") balance...first test on 10m behind the S-match tuner shows a reasonable balance. It's not perfect but close, nothing is perfect in the real world.

On 20m, the system behind the S-match is almost perfect in balance.


Left is 50W on 60m with the Palstar AT1KM (with 1:4 ruthroff balun inside).
Right is 50W on 60m with the S-match.

It clearly shows a unbalance with the Palstar, the S-match does a fine job in balancing.

I can show more pictures but it is not necessary I think. Other bands all showed the current in balance. I also tested with the Palstar, except 60m all other bands had a balanced current on the open line.

Well, I finally managed to get the meters in a box...

The tiny lightbulb lighting in this combo was still intact. Wow, it looks pretty nice...
Scrap parts remember! It looks very professional after all...