OK, let's say I have a half-wave 300-75 ohm balun cut for what I think is 94.5 MHz (PBS FM Buffalo) and it is connected for testing between the back of an FM tuner which is tuned to 94.5 and the roof antenna. I am watching the signal strength meter.

What would I do (or what components would I add to the circuit) in order to trim that balun to peak the balun for that frequency (besides the demanding activity of adding or subtracting bits of coax to the half-wave stub)?

Or a related question, what would make that balun more sharply tuned (thus acting as a passband filter) for that frequency or band (like using 1.5 wave stub, RG58...)?

Ben, Lemme see if I understand what ur up to correctly. You are trying to receive WNED FM (PBS) out of Buffalo, but it's being interfered by stronger local stations? And your using an outdoor antenna, with a 75 ohm downlead?

Does your FM tuner have a 300 ohm input?

If it does, one thing ya may wanna try is a 1/4 wave stub at the antenna
terminals of ur FM receiver to notch out the strong adjacent channel. You can use 300 ohm twin lead. Once ya have it trimmed "close enough", ya may be able to use a bit of tin foil, like a 1/2 inch or so wide, wrapped around the twinlead, ya then slide it up and down to fine tune the notch.

That trick used to work like a champ back in the day for eliminating TVI on certain VHF TV Channels.

If I remember right, without googlin or looking up in reference...
a stub open circuited at far end => acts like a Short circuit at 1/4 wavelength (i.e like a notch filter)
a stub short circuited at far end => acts like an open circuit at 1/4 wavelength (like a band pass)

Don't know if something like that would work for you or not,
but it's certainly easy enough to try, and easy to make adjustments.
Doubt ya could do that with a coaxial cable as a stub, because it's shielded and the foil
would have no effect.

Majortom - thanks for your thoughts.

I am at fault for neglecting the context of my request (earlier posts have it): avoiding the roof as much as possible, using a DIY half-wave balun instead of the sometimes-good-sometimes-bad commercial baluns, and having a modest degree of filtering for RF outside the FM band.

So the issue isn't so much avoiding one particular channel with your stub suggestion but making a low-loss balun.

No my new hot Sony tuner doesn't have a 300-ohm input but my "test tuner" does and that is the set-up I described for fine-tuning the balun.

At the moment, I'm OK for FM-stereo from Buffalo but sub-par for FM-HD. I plan to get a hotter antenna but want to fine-tune a half-wave balun to the new antenna in the backyard before hoisting it to the chimney. I'd like to think this system-concept has general interest to those reading this thread.

OK, let's say I have a half-wave 300-75 ohm balun cut for what I think is 94.5 MHz (PBS FM Buffalo)
Heh.. Ah.. trying to avoid that new double-power interference source from Hamilton, eh? :)

We gave up on that, and now listen to WNED-FM via internet-radio. Not as good quality as the OTA version was until last fall, but better than having it with that Hamilton disco-club beat fading in/out !

Cheers

Heh.. Ah.. trying to avoid that new double-power interference source from Hamilton, eh? :)

We gave up on that, and now listen to WNED-FM via internet-radio. Not as good quality as the OTA version was until last fall, but better than having it with that Hamilton disco-club beat fading in/out !

Cheers
Yes, from Ottawa, sadly, WNED-FM Buffalo seems hopeless if a Hamilton station is close by.

But the reception compass is favourable from Toronto. Even my little Winegard 6000 (2 driven elements) gets WNED-FM 94.5 in FM-stereo quite good on a Sony. And HD on some nights. Quality sound and classical music are my goals.

Footnote: the Sony does magic tricks with noise and bandwidth on weak signals and will output quite nice stereo sound down to flea-power signals. It will sound far better to my aged ears than say, "cassette sound" on almost any signal. I'm OK with that quality but still aim for better if I can get it.

Yes, from Ottawa, sadly, WNED-FM Buffalo seems hopeless if a Hamilton station is close by.
From Toronto, actually (mother-in-law). Her home seems to be on nearly direct alignment with that disco beat from Hamilton that doubled power last October, wiping out most of WNED-FM after 30+ years for her.

Thank goodness she has a good internet connection! :)

I suppose we could also get it there as a subcarrier on the WNED HDTV channel, which is quite viewable on a cheap [banned brand name] 4-bay bowtie UHF antenna.

Cheers

Hi

Just in response to my own question about steren baulns the 200-495 that I got - jup the wires are not fix in a twinlead package I placed on my 4228 cm test bed antenna.

The result was good the picture improved I maintained cross wiring disipline and was happy with the result as these ones are full weather capable the old dollar store ones were indoor types. The only down side was that my combiner was trashed so I had to use a new chepo ? :p kind from the buck store . I noticed that pico maco makes or devises the uvsj combiner and for some reason was able to trace that back to steren as the manufacturer ?

Can someone verify that as fact, if so I found a place that sells em for a good price so I'll be ordering a few in the future to fully upgrade the cm 4228 with a nice set of hacked equipemnt........ :rolleyes:

soooo nerdy , but who cares what a nice pic !!!

I noticed that pico maco makes or devises the uvsj combiner and for some reason was able to trace that back to steren as the manufacturer ?

Can someone verify that as fact, if so I found a place that sells em for a good price
Your profile shows "Ottawa" as the location.
In which case you are welcome to dig into my goodie bag of Pico/Macom UVSJs for a twoonie a pop, here in Bells Corners.

I get them from Active Surplus in Toronto, and redistribute them to dc.ca members locally as needed.

:)

I recently purchased an assortment (well what was supposed to be an assortment) of new baluns for testing in my OTA setup. What I actually received was 12 identical Magnavox 61009 baluns (which are in fact very good in my testing so far, by the way). Upon complaining about this, the retailer sent me, at no cost, 3 new Channel Master baluns and 3 baluns that are new to them and not yet listed on their website. They didn't know the brand.

I picked them up today and am surprised at their build - they are stubby, solid and heavy little things (marginally heavier than the larger CM baluns). The leads are short pigtails and comprise solid copper, probably about 16 gauge (i.e. slightly thicker than the 18 gauge aluminum leads on the CM), fitted with small ring terminals on the ends. The only marking on the things are "Matching Transformer". I've posted a picture below, showing the CM balun on the bottom for comparison.

Anyone know anything about these or have experience with them? I'll be testing later tonight (of course I'll have to extend the pigtails...) but wanted to see if anyone else had used something similar before. If they end up being good, it would be nice to know how to find them again...I don't think they would be Philips/ Magnavox as they are a significantly heavier/ more sturdy build.

http://www.digitalhome.ca/forum/picture.php?albumid=314&pictureid=2461

The bottom one is a dead ringer for a high-end Phillips balun. Bob at Mapleleaf Communications swears by them, when he's not making his own that is. ;)

That bottom one is the Channel Master one. I haven't seen a Philips one that looks like that - I wonder where Bob finds them...

Mlord, I think even you would be pretty impressed with the mystery one's build quality - it almost feels like high density rubber (not the usual cheap looking glossy plastic). Of course, it all means nothing if its performance is the pits...

For pure balun testing, just hook a low power transmitter to a receiver/meter/scope via your balun. Eliminate the antenna altogether.
Seems eminently implausible to test an impedance matching device by connecting one end to something (like a signal generator or transmitter) which has a different, odd, unknown, or otherwise not-the-same impedance using connectors that are different, odd, etc.

Or worse as you suggest, to connect BOTH ends.

Please correct me if I am wrong.

I noticed that mclapp has mentioned something about his balun tests today in another thread that he's said at our site a few times in the past:I've tested a number of commercial baluns in the field and found no real advantage reception wise between any of them. I like the channel master balun for its strength.

I noticed that mclapp has mentioned something about his balun tests today in another thread that he's said at our site a few times in the past:

Not a universal truth, though. I have had some extreme sample variance in baluns here. Eg. two "identical" Magnavox baluns: one good, one very bad.

It was somewhat embarrassing when I showed up at Bob's to test the GH8, and he asked if I'd ever received *anything* with that setup. We swapped the Magnavox for one of his Phillips (?) baluns, and suddenly his test equipment could "see" things.

Cheers

In light of the helpful information imparted by the last few posts (not to mention any wisdom in my summary above, #575), it seems all the more important for the sages of this thread to direct their good minds to:

how can the ordinary person conduct informative and comparative balum tests at home at the downstream/indoor end of the line? What basic affordable "test" set-up will be helpful?

Please.

I noticed that pico maco makes or devises the uvsj combiner and for some reason was able to trace that back to steren as the manufacturer ?
Dunno who makes them, but I have a large bag full of PicoMacom UVSJs here in Bells Corners for Ottawa folks. Give me a shout if you want a few -- twoonie apiece.

Cheers

In Post #589 the bottom balun is the Channel Master 94444. Several Canadian OTA suppliers keep them in stock.

What does a matching transformer do?

In an OTA TV context, it generally refers to the balan transformers used to match impedances. Years ago, TV antennas generally used balanced 300 ohm "twin lead" and the the TVs had the appropriate input. Later, unbalance 75 ohm cable became common and TVs followed suit. The balun transformer converts the impedance between 75 & 300 ohms and also connectes unbalance coax to balanced 300 twin lead.

What does a matching transformer do?

In an OTA TV context, it generally refers to the balan transformers used to match impedances.

Yup, simply put, assures maximum power transfer between two circuits.
So, in the OTA context, it assures maximum power transfer between the
antenna (typically 300 ohms) and the receiver (nowadays typically 75 ohms).
By making the receiver look like 300 ohms to the antenna, and making the antenna look like 75 ohms to the receiver.