[schoolbus]

Is it possible to run 2 Co-ax type baluns, in parallel, tuned for different parts of the UHF band?
That way, the losses away from the ideal tuned frequency, would be minimized.
Schoolbus

 

[rabbit73]

No, it wouldn't work, and it isn't necessary. A half wave coaxial balun will cover the UHF band with loss that is less than a ferrite core balun.

The major problem you will have is how to waterproof it.

 

[schoolbus]

Why wouldn't it work?
schoolbus

 

[rabbit73]

Because when you connect the two halfwave coaxial baluns in parallel they present an impedance of 150 ohms to the feed point of the antenna for a 2:1 SWR mismatch. And then you have two lengths of 75 ohm coax hanging down to connect to the coax feed line. How are you going to do that?

Please draw a diagram of what you want to do, so that I understand your plan.

Or better yet, why don't you make two baluns and connect them to your antenna and tell us what happens.

 

[goforit]

Installing Coax Cable to Balun with Weather Boot

I'm trying to connect a coax cable to a balun (see pics), but it has this heavy duty weather boot; not sure how to connect.

Slice the weather boot to increase the hole, pull the boot off the balun (tried but doesn't want to come off), or...?

Thanks.

 

[rabbit73]

Very odd. Who makes that balun?

It looks a lot like this one:
http://www.vetco.net/catalog/product_info.php?products_id=826

If it is, the boot has been forced on too far.

 

[goforit]

I got it from Summit Source. I did eventually get the boot off with a lot of tugging...

 

[rabbit73]

Good; thank you.

 

[Zank Frappa]

I recently ordered 2 very cheap baluns off ebay that I intend to use on a pair of ganged VHF antennas. They looked exactly like my CM94444's that I bought through radio shack/the source. When I got them they were different, it's obvious they are hollow in comparison to the CM94444's which seem solid. I tested both out on my FF4 antenna and they were MUCH better than the CM94444's on VHF with no discernable difference in UHF.

Normally CFTO Toronto comes in around 50-60% ss with the CM94444's, these "knockoffs" gave a reading of 86-90%, when I tried pulling in WICU (rf12), which is tropo only for me, I got nothing, not even a "poor signal strength", switched to the cheap Chinese Balun and low and behold it gave me a nice picture at 40%ss, switched back nothing.

Since Sunday night I've been getting WICU every night in good quality BEFORE I get WJET (which is my true tropo from Erie), this NEVER happens using the CM94444's, WICU is always the more difficult to get and more often than not unless tropo is really strong out of Erie I don't get it.

From what I've read this doesn't make a lot of sense unless CM had a run of bad product and both my others are part of that bad batch.

P.S. The Source in Canada no longer carries them, that was why I ordered off flea bay.



P.P.S. I got a pair with weather boots for less than $3 delivered.

 

[holl_ands]

I measured lots of different Indoor & Outdoor BALUNS....they all had significantly LOWER Loss in FM Band than UHF.
In the four BALUN's that ADTech measures (incl CM94444) Loss in Hi-VHF Band was UNDER 0.5 dB.

So your old CM94444's have probably been degraded due to Absorbed Moisture and/or Static Electricity Breakdown....or perhaps the oxidization on the coax connectors was disturbed when you first changed Baluns (in which case you might find the CM94444's NOW work the SAME???).

 

[Zank Frappa]

Both my CM94444's are less than 2 years old and one hasn't ever been used beyond a couple days trying to make the dual ganged ff4 work (too unwieldy). I tried the unused one and it matches the one I've had on for a year and a bit, no difference.

I bought the new pair only because The source no longer carries the CM94444's and these Chinese ones looked the same. I guess those CM94444's were a bad batch.]

 

[wildwillie]

You guys get this 4:1 coax cable balun figured out yet for VHF hi and UHF
My bow tie rat rod is running one lol

 

[holl_ands]

FYI: Updated Ferrite and PCB Balun Loss Summary and Charts:

http://www.digitalhome.ca/forum/186...-balun-perfomance-evaluation.html#post3039322
https://imageevent.com/holl_ands/files/ota [Charts towards bottom of webpage]

 

[DXING.Bruce]

Hey: Guys.

I just found a great place that sells older NOS tv preamps.

After reading the above post with respect to using a uhf
antenna with 300 ohm output & a preamp with a 300 ohm
input to prevent balun losses, this is the perfect model.

It has a 300 ohm input & a 75 ohm output.

I will be using my old school Channel Master 4221 with
the new preamp. I will post results when I get it set up.

They also list models with both the input & output
with 300 ohm connections for those die hard twin lead users.

Also listed are vhf / uhf preamps & much more.

I just ordered the Blonder Tongue Galaxy III uhf only preamp.

The store catalog # is 5119.

Here's the link for the store.


https://www.electronicplus.com/content/ProductPage.asp?maincat=ano&subcat=ano

 

[ProjectSHO89]

For every 300 ohm input preamp I've ever seen, if you open it up, the first thing you see is a balun.

 

[Gentleman]

For every 300 ohm input preamp I've ever seen, if you open it up, the first thing you see is a balun.

Correct. However would it not be advantages to minimize critical signal loss from the antenna terminals to the preamp input using low loss twin lead when it's DRY or the use of 300 ohm ladder line? Holl_ands?

 

[holl_ands]

IF using a very Low Loss Outdoor Balun (i.e. abt 0.5 dB using Philips, PCB or 4:1 Coax Type) then it is likely Better than a 300-ohm Input Preamp, nearly ALL of which are OLD Designs and hence are likely to use OLD Internal Baluns with MORE than 0.5 dB Loss.

Preamp "should" be Mast-Mounted, with very short wires connecting to Antenna. NO need for Twin-lead [and associated Loss when Plastic Insulation gets Wet]...just the short pig-tails coming out of a Cylindrical Balun....or short wires connecting 300-ohm Antenna Terminals to 300-ohm Input Preamp....kept at a constant wire-to-wire distance....and NOT twisted.

There is NO SITUATION in which Twin-Lead should be used OUTDOORS....it WILL eventually get wet and/or encased in Snow/Ice. And it should always be kept away from other objects, using stand-offs....so it WILL be degraded if run THRU the Walls....esp. if run thru metal or PVC Conduits....

PS: Old Preamps belong in the Circular File....esp if formerly used Outdoors...and even when New, many didn't meet claimed specs:
https://imageevent.com/holl_ands/files/ota?p=12&n=1&m=-1&c=3&l=0&w=1&s=0&z=4

 

[ExDilbert]

The best scenario, which I haven't seen in many years, is to mount the preamp on the antenna and connect it with short wires, not twinlead. If the preamp was designed without an internal balun, that would be even better. It is possible to design an amp with a balanced input. Don't know if that's practical with an RF preamp.

 

[Gentleman]

ExDilbert,

I believe the Channel Master Quantum series antenna was made this way. The preamp was encased in the boom of the antenna with the driven element directly connected to the preamp input.

 

[HRE]

I used a circuit simulator to model a halfwave balun. T1 is a transmission line whose length is an electrical halfwave.

Here are the model results for a halfwave of 75-ohm coax. The Y-axis is mismatch loss in dB and the X-axis is frequency in MHz.

I decided to build a balun to validate the model. I used 93-ohm coax because it should have only 0.24 dB loss at the band edges and I just happen to have some around. In fact, I located an 8.5" piece, which is what I calculate the length should be for 585 MHz, the arithmetic center of the 470-700 MHz band.

I cut 1/4" of vinyl off the ends of the cable, mashed the shields together, and soldered them. I stripped 1/8" of dielectric off the center conductors and soldered a half-watt resistor that measured (before heating it!) within an ohm of 300 across the tips. The tips touch the resistor body, with 3/8" of excess resistor lead length hanging in space (I may want to use this selected part for another project). I soldered a few inches of 75-ohm RG-6 to the balun using the shortest leads I could manage. I plugged the male F-connector on other end into my power splitter.

Minimum return loss for the balun occurred at 555 MHz so I centered my 200-MHz spectrum analyzer passband there. The power splitter return loss (open-circuit reference only--too hard to short the female F-connector on the power splitter) was 32 dB at 455 MHz, 33 dB at 555 MHz, and 29 dB at 655 MHz. The balun return loss was 15, 19, and 12 dB for the same frequencies. This is equivalent to SWRs of 1.43, 1.25, and 1.67, and mismatch losses of 0.14, 0.06, and 0.28 dB. Although a bit lopsided because I didn't quite center the response, this isn't all that far from the 0.17 dB that the circuit model predicts 200 MHz away from bandcenter for 93-ohm cable. I don't have an independent way of assessing what the 300-ohm load looks like over this frequency range.

I think this is a nifty balun for UHF-TV, particularly if you can get your hands on a few inches of 93-ohm coax (RG-62).

Brian

You use a 1/2 Wave balun to get 300 Ohm unbalanced to 75 Ohm Balanced. I am looking to get 150 Ohm unbalanced to 75 OHm balance. So is it a simple matter to replace the 300 Ohm Resistor which a 150 Ohm restor ?