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Ahhhhhh, there's a great idea for a testing strategy inside holl_ands post. To overcome the unpredictable variation in signal level when doing measurements, a person could use a Cable feed.

Is it correct to say that the Cable companies keep their signal level pretty constant?

Now.... at the other end, we need something to measure signal strength. I am not at all clear what the display on a TV means. I suppose I might understand it better if I had any idea who point in the TV's circuit drove the display.

Also, say a display had 10 "bars". Are these more or less linear with signal strength or are they a power function whereby the lower bars are more sensitive?

Ben
 

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Cable signal levels have some statistical fluctuation (just like OTA ATSC) and
vary by up to several dB from one QAM carrier to another....so you have to
measure each carrier before and after insert Balun and should then go back
and verify that signal level without Balun didn't change...and use the difference.

Unless there is a specific signal level in dBm, forget trying to use a "Signal Quality" display.

Some CECBs have been calibrated against a Signal Level Meter, see rabbit73's
post #10325 on 3/31/09 in the Antenna thread:
http://www.*************/t/381623/t...nd-related-hardware-topic/10320#post_16166929
[You know...in that other forum that shall remain nameless.....]

BTW: There is a Signal Level Meter thread on this forum.
 

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Otherwise, you'd need a programmable RF signal generator (ebay, several hundred bucks) plus an RF power meter plus time and patience.
Rather than use a RF signal generator, a better option would be to use a tunable RF modulator (You should be able to pick one up fairly cheaply online), that way you have a real signal you can tune to.
 

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It is possible to switch baluns on an antenna to see which one is better for a particular channel, but OTA signals can vary in strength. The ultimate test, however, of a balun is how it performs with your particular antenna. I use the following setup to measure balun loss:



Be sure to use good quality A/B switches, the slide-type switches that are in a case like a splitter don't hold up very well.

When I use my analog signal level meter, it is possible to interpolate to the nearest 0.1 or 0.2 dB, especially at mid-scale where the 1 dB divisions are wider. When I use my digital signal level meter, it reads in tenths of a dB.

It is not necessary to spend a lot of money on a signal level meter if you are careful to buy a good used one. An old analog meter will work fine because you don't need absolute accuracy of the dBmV value, just good linearity of the dB scale which can be checked with the built-in attenuator. I got this meter for $50:



When I must have a steady signal, I use a Channel Plus CP5415 or a Blonder Tongue HAVM-1UA modulator as suggested by roger. If you connect the modulator to an antenna to radiate a test signal and receive that signal with your antenna under test, you can switch baluns without worrying about changing signal strength. The test signal must not be any stronger than necessary to avoid interference; it should be similar in strength to a tracking generator in a spectrum analyzer.
 

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Inexpensive baluns - 'AIM 2000' brand

Check out ACK Electronics, they have warehouses in Atlanta, GA, & Birmingham, AL. The general public can walk-in, and you can also order by phone or email to have items shipped. Not sure if they ship to Canada, but probably do. Their website sucks, so call or email. You can find their contact info from a web search, but again, their 'online catalog' is useless, don't waste your time downloading it!

Bought a half-dozen baluns branded 'AIM 2000' for $.79US ea., and they work the same or better than any others I have bought costing $3-5 ea.!!! :D

BTW, the Radio Shack outdoor balun really DOES suck - what a waste of $5!
 

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Anyone know in Toronto where I can walk in and get a new ballun? I see I can get the CM 9444 if I order online from The Source but don't really want to wait for it to arrive...
 

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alebowgm,

I know of three locations in Mississauga:

1. SaveAndReplay at 6355 Kennedy Rd.
2. Angel Electronics at Dixie Rd and Matheson Blvd.
3. A store next to (or next to next to?) Sayal Electronics also at Dixie Rd and Matheson Blvd. I don't remember the name of this store, but it is in the same "strip mall" as Sayal.

You can Google these stores to find their exact locations on a map.

Hugh
 

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Hugh,

Thanks for the reply. Since I have mostly given up the car, none of those are close/accessible. Also, doubt I will have a chance to make the adjustments I want until next weekend, so went and ordered it from The Source. By the time it arrives the end of this week, I should be getting some free time to fix my (original) CM 4228.
 

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Bad ballun?

Do balluns just stop working? Came home yesterday and the TV and radio were working fine, today I only get one of the strong FM radio station. I spliced in an FM antenna in the line, and I can pick up the other FM stations, but no TV stations. The power supply for my amp is putting out 24 VDC (CM-7777) and there's no visible damage to the antenna (CM-3671). I don't want to take the tower down just to check the connections. Is there a (simple) way to test the system thru the cable?
 

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Like anything else, they can fail. Perhaps an internal connection has gone bad. Have you tried a continuity test?
 

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Please pardon me if the answer has already been given. I've checked links for balun loops for the right length of loop for a cm4228hd at about rf35 and haven't been able to figure it out. What length of loop should I use?
 

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A balun loop would be fine with an antenna cut for a specific frequency, nothing else.
Wrong and wrong again. I used only balun loops to get all my channels, local channels from RF15 to RF39 + extra channels when the tropo is good. If your local channels are strong and the RF35 you want to get is weaker, give it a try. Even a UHF cut loop balun can get a VHF channel if it's strong enough. I've been doing this for over two years
 

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New2OTA,

Doing so, you will jeopardize the reception of other channels.

A balun loop would be fine with an antenna cut for a specific frequency, nothing else.

A CM4228HD as is does already great for RF 35.

And what do you mean by "CM4228HD balun hacked" in your signature ?
.
True enough although the amount of discrimination is not large. Often it is a single freq that is the target of the tuning.

If I may give an example from the fm band, I've been keen to make a loop balun to get PBS-fm 94.5, remote in Buffalo. All the local stations might be overloading my front-end already! I think there's some possible benefit for 94.5 but I doubt there's any cut to local CBC-fm at 94.1 with a tuned balun.

Anybody know how sharp is a loop balun tuning curve?

BTW, the instructions on the web look superficially wonderful until you get out your wire cutters and try to figure out the performance of the no-name or odd cable in your hand or whether or not the pig-tail solder lead counts in the measurements, or whether.....

Ben
 

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K6STI modeled the Loss of a 1/2-wavelength Coax Balun across FM Band and found less than 0.12 dB. Baluns designed for Hi-VHF or UHF Band (can't do both at once) will no doubt have somewhat higher Loss...but should be no worse and usually better than 4:1 Transformer Balun:
http://www.ham-radio.com/k6sti/balun.htm
[At END of webpage, first is a simple COIL of Coax, which is ineffective in UHF Band]
 

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New2OTA,

And what do you mean by "CM4228HD balun hacked" in your signature ?
not the original poster, but a CM4228HD as shipped has a single balun.
One well-known hack is to put a balun on both sides of the antenna and combine the output with a splitter/combiner
 

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K6STI modeled the Loss of a 1/2-wavelength Coax Balun across FM Band and found less than 0.12 dB. Baluns designed for Hi-VHF or UHF Band (can't do both at once) will no doubt have somewhat higher Loss...but should be no worse and usually better than 4:1 Transformer Balun:
http://www.ham-radio.com/k6sti/balun.htm
[At END of webpage, first is a simple COIL of Coax, which is ineffective in UHF Band]
Many thanks for detailed reply. I gather the ".12dB" is the worst-case, that is, the loss at the freq furthest from the tuned freq?

I wonder what is the biggest gain-advantage of using a coil balum compared to a pretty-good-working off-the-shelf balun or a printed-circuit "balun" attached to the antenna?

I suppose you mean that the bigger out-of-tune losses at UHF are due to UHF band being proportionately wider than the 88-108 FM band.

Ben
 

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As shown in K6STI's chart, Half-wavelength Coax Balun has highest loss at the lowest and highest Band frequency and lowest loss mid-band. UHF will have higher loss due to trying to cover a much wider bandwidth and may also have somewhat higher parasitic losses (higher loss at UHF Freqs is roughly offset by shorter coax length than for FM....or Hi-VHF).


In Mar2011, ADTech posted Balun Loss for two commercial Baluns and A-D's UHF-ONLY UP2A-6 PCB Balun (bundled with the Hi-VHF C5 Antenna to combine with an external UHF Antenna). UHF Loss is EXCELLENT, under 0.4 dB. Presumably not available as a catalog item:
http://www.digitalhome.ca/forum/showthread.php?p=1233360

In Jan2011, ADTech measured Loss for four commercial Baluns (back-to-back so divide numbers in chart by 2). Loss was about 1 dB (or a bit less) in Hi-VHF Band and ranged from 1-4 dB in UHF Band:
http://www.digitalhome.ca/forum/showthread.php?p=1214991

In Feb2009, Johnrmckee posted the LOWEST LOSS measured for a conventional 4:1 Transformer Balun, a Philips OUTDOOR Balun (0.5 to 0.9 dB):
http://www.avsforum.com/t/798265/how-to-build-a-uhf-antenna/1710#post_15851345

In Apr2008, I posted Loss measurements for quite a few commercial Baluns, finding even HIGHER Loss (6 dB worst case) in the UHF Band depending on frequency and manufacturer:
http://www.avsforum.com/t/381623/th...and-related-hardware-topic/7830#post_13581150

PS: In ADTech's charts, 0 dB Loss line is the MIDDLE line (not the top).
Most charts are 2 dB/div, except PCB Balun is 1 dB/div.
In most charts, CENTER line is 500 MHz, so far left is 0 Hz and 200 MHz is second line from left
and 700 MHz is two line to right of Center.
Carefully read the post, most results are for TWO back-to-back Baluns, so divide by TWO.
 
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