300 ohm wire, max length??
 

Hello,

I have a Channel Master CM-5020 antenna which connects to the balun and then directly to the tv. The antenna is only about 18 months old. In that short time I have had to replace the built-in balun with a CM-94444. It looks like that balun too is failing because I have the same symptoms of intermittent, random loss of channels.

My question is, can I run some 300 ohm wire from the antenna to inside the house and then attach to the balun? I really hate going up on the roof to replace baluns :( BTW I'd estimate the wire run would need to be around 50 ft...

Here is my TVFool report:
http://www.tvfool.com/?option=com_wr...9038f3360d6a26



Thanks for your help,

Don Verbeck

I may have found the answer. I understand that unshielded 300 ohm twinlead can experience interference if its run near any metal. It requires experience to run the 300 ohm. So I guess I'd better go with the coax. Does anyone have any balun recommendations?

Hello BigHenry:

Here's your rabbitears.info report. Unfortunately, it looks worse than your TV Fool report, which may not be as up to date as the rabbitears.info due to a very small staff trying to keep up with repack, etc. It takes about 20 seconds to load:

https://www.rabbitears.info/search.p...=dBm&height=20

Anyway, assuming you were getting reasonable reception before your balun issues, here's a link to an earlier TV Fool thread by rabbit73 which I have found very helpful at my location and not to mention, an inexpensive option as well! If rabbit73 chimes in, I'm sure he could elaborate and give you further advice.

http://forum.tvfool.com/showthread.p...ed=1#post58266

All the best and please let the forum know how it turns out for you. Thanks.....

Thanks for the reply OTAFAN. Yes, the RabbitEars report looks dire. My reception was pretty good when my second balun was new. We live on a hill and have the antenna up high on the roof peak.

I'm still unsure what kind of balun to try next. Lowes has a cheap one that I believe is an iron core type. The CM-94444 I currently have is of the circuit board type. In my simple mind a basic core seems more sturdy than a circuit board?? I think I'll order another CM-94444 and swap it out when the weather improves.

While I think I have a balun problem, I'm open for other suggestions. One thing I noticed this morning (about 7 AM) is that I have all my channels back (7.1, 7.2, 10.1 -10.5, 15.1-15.4, 24.1, 38.1-38.6) and the TV's signal strength meter is around 70 where it is normally in the 10-25 range. Beautiful picture too with no pixelating. Normally in the afternoon/evening we only get the 38's reliably, the others randomly pixelate or indicate "no signal". Weird....

It sounds like you might be on the edge of the digital cliff, rather than balun problems.

If you think otherwise, you may consider making your own 4:1 balun. Google ½ WAVE LENGTH COAX BALUN for suggestions.

Running 50-feet of twin-lead down to the ground isn't a bad idea. There is special hardware to achieve standoff between your mast and other metal along the path.

Thanks for your input, jrgagne99. Is a "Digital cliff" referring to where the TV signal just drops off?

I have been recording signal strengths for the 7's, 10's, 15's and 38's channels today. They have all been in the 30-40% strength range, which is just fine for a good picture. The 7 channels are a bit lower but WDBJ has a known transmitter power issue.

We last had rain about 3 days ago and each of those days lousy reception on all stations except the 38's. Maybe the balun has dried out? ;) I'll keep recording signal strengths. If my readings are still good tomorrow, I'll take a trip up to the roof and look more closely at the baluns water-tightness.

Rain in a PC board balun will definitely cause signal loss. I had it happen on another antenna, not the CM-5020. The bad thing about water intrusion into the balun is that it is then possible for the water to infiltrate your coax (depending upon the balun design).

Yes, that's what I'm referring to.

Percentages like that are useful, but not especially quantitative, IMHO. You kind of need to identify where pixelation begins to occur to make any sense of actual signal strength. The best indicator I've seen on a standard TV is on the Sony Bravias, which usually list signal to noise ratio (SNR) in dB. SNR of 15 is crystal clear, 14 has intermittent pixelation, and 13 is gonzo. You typically want to be around SNR=20 so that even in adverse conditions, the SNR stays above 14. Every 3 dB additional is a doubling of signal strength. I doubt that 40% is twice as strong as 20% on your TV, since mine goes from 15 dB (watchable signal) up to 34 dB (~80x stronger than 15 dB).

Tim, when the CM-5020's original "built-in" balun failed I called Channel Master. They stated that I could not get an exact replacement balun, instead all they offered was the CM-94444 in-line balun. I had to cob the CM-94444 on to the frame of the CM-5020 antenna. I sealed it as best I could with 3M black mastic tape so it's possible its leaking. When I replace the balun with a new CM-94444 I'll simply let it hang down with the protective boot over the coax.

jrgagne99, here is the antenna performance data I gathered. Pixelation occurs at 10%. Isn't it interesting how the reception degrades for the channels 7's and 10's as if there is a temp dependence going on here.

Time Weather Temp Chan 7’s Chan 10’s Chan 15’s Chan 38's
0820 Cldy 32 62 60 64 78
0840 Cldy 33 40 44 65 73
0925 Cldy 34 38 52 62 57
1030 Cldy 38 41 42 58 58
1115 Cldy 41 10 33 59 42
1205 Cldy 44 23 35 53 45
1320 Cldy 45 No signal 10 59 38
1420 Cldy 48 No signal No signal 60 40
1540 Cldy 49 10 10 No signal 39

Sorry about the crummy looking table. All of my tabs were ignored.

Here is the table as an attachment

Hello, BigHenry; welcome to the forum.

Thank you for the signal report. Here is a report based on your exact address instead of your zip code from rabbitears.info:
https://www.rabbitears.info/searchma...study_id=33265

This image is an extract from that report:

https://forum.tvfool.com/attachment....7&d=1575676969

What happened to the original balun, did it break or did it just not perform the way you thought it should?

I agree with jrgagne99, your signals are marginal. Reception will vary according to atmospheric conditions, and rain will affect the trees in the signal path, making the signals weaker.

You could use 300 ohm twinlead, but you would still need to use a balun at the lower end.

In what way did it fail?
That's really poor support. They sell you an expensive antenna and then they will not send you an original replacement balun.
You need a ferrite core balun to cover all three TV bands, VHF-Low (real channels 2-6), VHF-High (7-13), and UHF (14-51; soon to be 14-36).

A halfwave coax balun is low loss, but it only covers one TV band.

There are two types of printed circuit board baluns. A UHF printed circuit board balun is only good for UHF.

https://i.imgur.com/q8jSCXc.jpg

There is a type of circuit board balun thay is good for all three TV bands because it has a ferrite core balun mounted on the board. You will only find this only on Winegard antennas.

https://i.imgur.com/mN07nXU.jpg

https://i.imgur.com/WEqjATF.jpg

I really don't know what is inside the CM-5020 balun; can you show us the inside of the one you removed?

https://forum.tvfool.com/attachment....8&d=1575681045

I suggest you use the CM94444 balun, but keep the leads short. It's an outdoor balun and should be waterproof.

Since your signals are quite weak, I suggest you add a preamp near the antenna, and run the RG6 coax down to the grounding block and then to the power inserter inside.

Hello rabbit73,

Thank-you for the updated report. All of the channels with the "Fair" field strength are exactly those I can receive.

This past summer, I suspected the OEM balun installed in the Channel Master CM-5020 antenna was not performing properly. At random times channels would pixelate to the point where the TV (Magnavox 39ME413V) would give up with a "No signal" condition. I wasn't really sure what was causing the problem, but since the balun was inexpensive I bought a CM-94444 and upon installation my problem was solved.

This time, as appears in my attached table, the march down from decent signal strength to pixelation seems less random and more predictable. So this time I'm not as confident its a sick balun, but again since its cheap I'll be ordering another CM-94444 and replacing it. Maybe the 4:1 transformer technology used in the CM-5020 OEM balun is different from the CM-94444 which may explain why their symptoms are different?

Any other insight is much appreciated.

rabbit73, for your suggestion of a pre-amp, would the Channel Master CM-7777HD be a good choice?

To your question on what's inside the CM-5020 balun, unfortunately I tossed it last August without looking inside.

The CM7777HD is a good preamp; I have two of them that I use as test amps for setups. But, I really don't like the housing because it doesn't seem suitable for outdoor use. Their other preamps have the connectors on the bottom which provides better weather protection.

https://forum.tvfool.com/attachment....0&d=1575730865

Their previous 7777 with the single antenna input doesn't have a good reliability record:

https://forum.tvfool.com/attachment....2&d=1575732193

Their new 7777V3 looks promising, but it is as yet unproven. I suspect it will be more reliable.
https://www.channelmaster.com/TV_Ant.../cm-7777v3.htm

https://forum.tvfool.com/attachment....3&d=1575734997

Well, I installed the new balun CM-94444 this afternoon. Because the new balun leads mount on top and fall on either side of the CM-5030 antenna frame, I felt I should not shorten the balun leads. I re-aimed the antenna using the same bearing where I detected good signals previously. Unfortunately, I don't receive the 7's and 10's but still get the 15's and 38's. I suppose the CM-7777V3 medium gain pre-amp will be the next thing we try.

I think you're on the right track with the pre-amp. Perhaps the balun has been a red herring?

The new pre-amp is installed. I went with the Wineguard LNA-200. Results not encouraging. Yes, I can see that my signal strengths for the stations I could already receive (15's and 38's) have been boosted. I saw a slight improvement on the 10's, it will pixelate and drop out instead of having "No Signal", but its not really watchable. The 7's are still out with "No Signal".

At this point, I can't see throw any more money at this. I'll just accept that antenna's are not suitable in my locale and go the starter cable route.

Don

Did you locate the pre-amp at the antenna mast?

WDBJ virtual channel 7.1 has an "R" in the right column of the rabbitsears report which indicates reduced coverage. They might still be using their low power STA transmitter with a directional antenna. It's only 10% of the normal transmitter power.
https://www.rabbitears.info/tvq.php?...ms&facid=71329

https://forum.tvfool.com/attachment....6&d=1576771719

Yep, the black plastic pre-amp is mounted on the mast very close to the antenna frame. I used a short (18") piece of RG-6 coax connecting the balun to the pre-amp.

Yes, channel 7 is only broadcasting at reduced power. They have been trying to get back to full power since September. I call them about every 2 weeks to get a status. They hope to resume full power by end of December.

That's good to hear, I miss having them as a backup to my local, (and sometimes crappy), CBS station.

rickbb,

I just saw WDBJ's website and they announced that the new transmitter is operational as of today.

I just called Shentel (our local cable company) inquiring about the price of basic cable. I damn near bit my tongue in two when the sales droid said that with taxes, surcharges, graft, et al, the cost would be a bit north of $50 a month. I'm re-motivated to keep trying OTA. What else should I try? Here are a few ideas:

1. Find a way to shorten my CM 94444 leads so that the balun still hangs down.

2. Try a new dropline from the antenna into the house.

3. Could my antenna have something physically wrong, bent metal or a short?

Any other suggestions?

How old is the dropline down into the house? Have you tried taking a portable TV right up there to the antenna to check reception there? No pre-amp is needed for this test.

I tend to doubt that a bent element would be affecting your reception so adversely.

Hey, some good news!

As suggested by rabbit73 in an earlier post, I figured out a way to shorten my balun leads to 2.5" while still able to mount the balun. As if by magic I'm now receiving solid signal strengths on ALL original channels (7.1, 7.2, 10.1-10.5, 15.1-15.4, 24.1, 27.1-27.4, 38.1-38.6.

I would like to thank all who helped me out, with a special thanks to rabbit73 for the balun testing leading to the discovery of an optimal balun lead length.

My balun attachment is rather ugly - the balun sits right alongside the main horizontal boom with one lead crossing over the boom, which looks OK, but the lead which attaches to the post on the same side of the balun is a bit compressed. Not as pretty as the long lead set-up where a lead comes down on each side of the boom, allowing the balun to sit on the centerline below the boom. But it's the results that count!

Frankly, antennas, baluns/leads and RF frequency waves seem like voodoo to me. Could any of you experts on the forum help me understand why shortening balun leads so dramatically improved my reception. Does the orientation of the leads also have an effect? e.g. like the leads in close parallel proximity or spread apart as far from each other as possible.

Lastly, as long as balun lead placement won't mess up my reception, I am thinking of inverting the threaded studs to which the balun leads attach, so they will now be beneath the boom and once again the balun will hang down on the centerline below the boom.

Thanks,

Don

My rule of thumb has always been, "If it ain't broke, don't fix it."

Thank you for the report of improved reception. I'm glad that my balun tests gave you an idea that helped. I hope the improvement will continue.
Antennas have always seemed like magic to me. I have been experimenting with them since I was 8; I'm now 86.
A little bit of luck helped both of us.

The wire leads from the antenna terminals to the balun form a transmission line. The transmission line transfers the signal energy from the antenna terminals to the balun. If the design of the transmission line is correct, most of the energy will reach the balun.

The transmission line must have the correct impedance and length to match the output impedance of the antenna terminals to the input impedance of the balun windings. The impedance of the transmission line is determined by the diameter of the wires and the spacing between the wires. My thought was to make it look something like the spacing of 300 ohm twinlead. Some baluns actually have 300 ohm twin lead instead of two separate wires.
My reaction is similar to Tim's. Don't mess with it if it's working. If you do mess with it, make certain you can put it back the way it was. The studs will become part of the transmission line.

When I was young, I built an audio amplifier on a breadboard using two 6L6 tubes in push-pull in the output stage. It worked very well. I bought an aluminum chassis and mounted the parts on the chassis. It didn't work as well.

When I was older, I built a regulated power supply for an electronic flash using transformers connected to form a saturable reactor to regulate the voltage with a small DC control current. I built it in an enclosure that I had on hand; it worked very well. I built a second power supply in a fancy cabinet with a carrying handle. It didn't work as well, and I never could figure out why.

Thanks again, Don for your report of success with the balun. I consider it a Christmas present from you to me.

Best regards,
rabbit73

rabbit73, I too consider good reception to be a gift, so thank-you. But reaching 86 years and passing on your knowledge is your greatest gift.

I had no idea that impedance of the transmission lines played such a critical role in matching the output impedance of the antenna terminals to the input impedance of the balun. So if my transmission line was a little bit shorter, longer, fatter, skinnier or orientated differently I might have missed the optimal impedance and continued to have crappy reception. Now I understand the "luck" factor.

I'm going to go back to Channel Master and ping them harder to get the OEM built-in balun, because unlike my "lucky" CM 94444 balun the OEM was probably engineered to have the proper impedance. The trouble with the OEM balun is that the terminal studs don't seal well in the housing and are a moisture trap. But I can seal the studs with some silicone to keep out the water.

The saga continues...

Any plastic housing for a PCB balun will trap moisture from condensation. The best designed housings have "weep holes" at the bottom to allow the enclosure to breathe and drain moisture.

Older Channel Master preamps like the original 7777 with two antenna inputs not only had the connectors on the bottom for weather protection, but the bottom plate wasn't tight against the housing. This provided a small gap at the edges of the plate to allowed the enclosure to breathe.

The recent preamps sold by Channel Master have a gasket at the edge of the plate and coax connectors that have an internal seal which makes it difficult to insert the center conductor of the coax. I'm not convinced that trying to make the enclosure hermetically sealed is an improvement.

https://forum.tvfool.com/attachment....7&d=1576957848

Well looky-here. In my shop trash, I found the old OEM balun that came with my CM-5020 antenna. I cleaned the water-induced oxidation off and will reinstall with better moisture resistance and some weep holes.

Actually it may be awhile before I install the OEM because the current CM-94444 balun is doing such an exemplary job. BTW, I cut open a spare CM-94444 and it is of the ferrite coil type, not a PCB. Based on what rabbit73 told us about getting balun lead impedance right, my gut feeling is that the OEM PCB balun is better tuned to the antenna than my lucky CM-94444. But I still don't want to risk it.

Good find! Thanks for the photos.

https://forum.tvfool.com/attachment....1&d=1577038712

https://forum.tvfool.com/attachment....2&d=1577038735

https://forum.tvfool.com/attachment....3&d=1577038755