Baluns (Brands, Designs, Losses, DIY Loops, etc.) - Page 44 - Canadian TV, Computing and Home Theatre Forums

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post #646 of 827 (permalink) Old 2010-08-31, 10:49 AM
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spas, when you bypassed the preamp did you bypass its power injector too?



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post #647 of 827 (permalink) Old 2010-08-31, 11:12 AM
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Yes I completely bypassed both CM7777 units. I just used two couplers - one out on the roof and the second to connect the tv to the outside antenna wire.

Steve
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post #648 of 827 (permalink) Old 2010-09-17, 05:24 AM
 
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I've been trying to compare the advantages for my FM antenna of a balum transformer (cheap, available, sort of a known quantity) with a half-wave matching balun (anybody's guess how a DIY RF device is working).

Question: a transformer with a 300:75 ohm windings ratio, should make the voltage in the secondary winding half - but a half-wave balum should provide the full voltage. That would be really good, eh. Is that correct????

With strong local signals on SDTV channels and only two degrees separating the CN Tower from my PBS-Buffalo source, very hard to anticipate the right balance of overload from too much antenna and under-powered signal from Buffalo.

A half-way balum can be peaked at the FM band and so disciminate to some (unknown???) degree against strong SDTV signals.

Thanks a lot.

midtown Toronto, DB4e, 60ft RG6, 8dB distr amp
FM: Sony STSA-50ES, Wine.6065, 40ft RG6
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post #649 of 827 (permalink) Old 2010-10-19, 11:22 PM
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Hopefully this is a better pot for my post. Read the thread, but it still did not answer my question.

I currently have 2 CM4221hds that I will likely stack. I may add 2 more just to see my girlfriends face when I tell her we now have 300$ equipment to save on cable fees...

Although I have read some lukewarm remarks about the benefit, I would like to try to connect both with 300ohm feedline and a 2:1 homemade balun, eliminating the stock baluns from the equation. With the 4 stacked antennas, if I read correctly i only need a 1:1 balun, correct? I feel that would be the greatest gain, because I would bypass a lot of splitter/combiner insertion losses. Anyone combine 4 cm4221hds yet? The safe path (and baseline performance)would be 3 low loss splitters, but I think the db savings may be worth the pain for 4 antennas.

Q1 Can I connect the 300ohm feed temporarily on the feedline strips holding the balun? Does it matter where I connect?

Q2 Will the stock balun interfere with my signal, even if it not connected?

I want to keep the mod reversible, and want to avoid messing about and cracking open the stock balun boxes, if at all possible. The stock cm4221hd balun is not crap by any measure, so I want to make sure i can revert ack to stock if i am not happy with my "mods".
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post #650 of 827 (permalink) Old 2010-10-20, 01:24 AM
 
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Best way to find out, is to give it a go.. Connect your 300 ohm nearest at the rivets and use equal lengths of cable to connect the 4. In theory, you should end up with a 75 ohm load nominal. However, when you combine 4 antennas SWR and signal strength will change as a result at various frequencies. I've used a 2:1 centered at 620 mhz on a dual CM4221HD setup with a custom feedline with good success. See here if you want to have a peek as to how I did it: http://www.digitalhome.ca/forum/show...=104837&page=9

I would remove the stock balun as it will change the results slightly when removed. think of it as adding length to both sides of the feedline thus detuning your setup.
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post #651 of 827 (permalink) Old 2010-10-20, 01:00 PM
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Spaced baluns from the strips

Mogwai,

Check out

http://www.digitalhome.ca/forum/show...104837&page=15

To me this may explain why you saw at least 3 db less with the CM baluns than with the cable loop balun. Apparently electrical connections at EXACTLY the midpoint of the phasing lines is crucial. Rabbit73 showed 1-1.7db improvement just by spacing the stock baluns off the strips, and making the rivet positions (which are well cenetered) the actual electrical connection.

Not to knock the coax balun, of course. But I will be doing the double spacer mod with reversed splitter first on my dual stack. Maybe I can compare it to your setup in a head to head

Are the stock baluns hard to open and drill out? I am always afraid to ruind 50$ pieces of equipment, that actually work ok as is...
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post #652 of 827 (permalink) Old 2011-01-20, 11:01 AM
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OEM balun for CM4221HD

Quest!

I'm looking for a parts source to find OEM replacement baluns for repairing CM4221HD antennas. I don't like the idea of using pigtail style baluns to patch/repair damaged CH4221HD antennas. Has anyone found a source for OEM replacement parts.

3D SSH III with ZZ4 refl. http://imageshack.us/user/jmsdigital
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post #653 of 827 (permalink) Old 2011-01-22, 01:52 PM
 
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Quote:
I was going to suggest using a Phillips Outdoor balun from Lowes or Walmart instead of the Radio Shack one, but it looks like its doing OK anyway.
I have a Phillips balun readily on hand and prior to this afternoon's testing, I did a comparision between it and the Radio Shack balun.

I was mildly surprised to see that the Radio Shack balun performed better than the Phillips-branded one. Using the Sencore POWER reading as my metric, the Radio Shack yielded better gain by 0.25-1.18 dBmV.

Since the measuring device (the SLM-1456) is used strictly as means to get tangible relative values for comparison, I think these results are valid. Thus, I'll stick with the Radio Shack 15-1230 balun when the shootout gets underway before much longer.

I'll also enhance the YA-1713 vs. Y10-7-13 data provided with waveform images from the SLM-1456 spectrum grab.
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post #654 of 827 (permalink) Old 2011-01-22, 02:05 PM
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Quote:
I was mildly surprised to see that the Radio Shack balun performed better than the Phillips-branded one.
Yeah, that is surprising, but baluns can and do vary among individual units and batches.

My builds/plans (not the latest models) are located here.
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post #655 of 827 (permalink) Old 2011-01-22, 02:17 PM
 
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Quote:
Yeah, that (Radio Shack 15-1230 outperforming the Phillips balun) is surprising, but baluns can and do vary among individual units and batches.
And to further flesh this out, the measurements were confined only to four high-band VHF channels (8, 9, 11 and 12) using an AntennaCraft Y10-7-13.

The advantage of the Radio Shack balun was most evident (> 1.0 dBmV) on channels 11 and 12. On both channels 8 and 9, the two baluns were very close but still an edge to the RS 15-1230.

As you said, batches vary and I may have just stumbled upon a subpar unit at Lowes for the Phillips balun.
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post #656 of 827 (permalink) Old 2011-01-29, 02:09 PM
 
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Balun comparsion using VHF dipole

300ohm states:
Quote:
...baluns can and do vary among individual units and batches.
As evidence of this, here's a four balun comparison focusing strictly on hi-VHF performance using a DIY folded dipole (made for me by a colleague at work). The measurements were taken using a Sencore SLM-1456 unit using a short (183 m) run of RG-6/QS from Monoprice. I attempted to change the balun as quickly as possible to eliminate any variable due to time. The high-VHF folded dipole was locked into place so that its position remained constant.

Since these are "point in time" measurements from the Sencore's "SAVE/SCAN" tool, take that into consideration as you examine them. I also welcome any suggestions to my methodology that may provide more meaningful data since nothing conclusive jumps out at me as I examine these data.

Code:
LOG1 - CM-3095 (CM0089) PN-94444 
--------------------------------
SOURCE      :  High_VHF                 
TIMESTAMP   :  2011-01-29 @12:36

+----+--------+-----+-----+-----+------+----+                
! CH.!  TYPE  !LEVEL! A/V ! MER ! BER  !DIG.!                
!    !        !POWER!     ! CCN !      !QLTY!                
!    !        !dBmV ! dB  ! dB  !      !    !                
+----+--------+-----+-----+-----+------+----+                
!  8 !8VSB    !-22.3!     ! 23.1!2x10-8!PASS!                
!  9 !8VSB    !-24.1!     ! 22.1!8x10-6!PASS!                
! 11 !8VSB    !-13.2!     ! 31.3! <10-9!PASS!                
! 12 !8VSB    !-26.7!     ! 29.3!3x10-8!PASS!                
+----+--------+-----+-----+-----+------+----+                

LOG2 - Radio Shack 15-1230
--------------------------
SOURCE      :  High_VHF                 
TIMESTAMP   :  2011-01-29 @12:39

+----+--------+-----+-----+-----+------+----+                
! CH.!  TYPE  !LEVEL! A/V ! MER ! BER  !DIG.!                
!    !        !POWER!     ! CCN !      !QLTY!                
!    !        !dBmV ! dB  ! dB  !      !    !                
+----+--------+-----+-----+-----+------+----+                
!  8 !8VSB    !-24.3!     ! 27.8! M.OUT!MOUT!                
!  9 !8VSB    !-24.7!     ! 16.9!1x10-4!MARG!                
! 11 !8VSB    !-13.2!     ! 32.1! <10-9!PASS!                
! 12 !8VSB    !-26.3!     ! 30.2!2x10-9!PASS!                
+----+--------+-----+-----+-----+------+----+                

LOG3 - New Phillips WALMART (obtained 20 JAN 2011)
--------------------------------------------------
SOURCE      :  High_VHF                 
TIMESTAMP   :  2011-01-29 @12:42

+----+--------+-----+-----+-----+------+----+                
! CH.!  TYPE  !LEVEL! A/V ! MER ! BER  !DIG.!                
!    !        !POWER!     ! CCN !      !QLTY!                
!    !        !dBmV ! dB  ! dB  !      !    !                
+----+--------+-----+-----+-----+------+----+                
!  8 !8VSB    !-24.5!     ! 24.0!1x10-7!PASS!                
!  9 !8VSB    !-26.3!     !M.OUT! M.OUT!MOUT!                
! 11 !8VSB    !-12.4!     ! 33.7! <10-9!PASS!                
! 12 !8VSB    !-27.7!     ! 31.2!2x10-7!PASS!                
+----+--------+-----+-----+-----+------+----+                

LOG4 - Old Phillips LOWES (obtained summer 2009)
------------------------------------------------
SOURCE      :  High_VHF                 
TIMESTAMP   :  2011-01-29 @12:44

+----+--------+-----+-----+-----+------+----+                
! CH.!  TYPE  !LEVEL! A/V ! MER ! BER  !DIG.!                
!    !        !POWER!     ! CCN !      !QLTY!                
!    !        !dBmV ! dB  ! dB  !      !    !                
+----+--------+-----+-----+-----+------+----+                
!  8 !8VSB    !-23.9!     ! 25.3!3x10-7!PASS!                
!  9 !8VSB    !-24.5!     ! 23.8!1x10-5!PASS!                
! 11 !8VSB    !-11.5!     ! 32.2! <10-9!PASS!                
! 12 !8VSB    !-27.0!     ! 29.9!3x10-7!PASS!                
+----+--------+-----+-----+-----+------+----+

Last edited by re_nelson; 2011-01-29 at 02:33 PM. Reason: Corrected obtained date for "New Phillips" balun (checked receipt)
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post #657 of 827 (permalink) Old 2011-01-29, 03:19 PM
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Based on the above, good thing I bought my Phillips baluns in the summer of 2009, heh. Channel 11 being my weakest vhf-hi station.

Since you still have the receipt, you could still exchange the new one at Lowes.

Looks the RS balun is the still the best for your channel 12.

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post #658 of 827 (permalink) Old 2011-01-29, 06:09 PM
 
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Balun comparsion using VHF (Y10-7-13)

I'm now back from the Saturday errands and have another set of data for the four baluns I compared earlier this afternoon. The previous readings were using a homebrew folded dipole. Refer to that posting (#656, above) for details about each balun shown below.

These readings were made using the REAR BOOM ONLY of the AntennaCraft Y10-7-13 thus yielding a 6-element antenna. Because the raw power readings made with a Sencore "SCAN/SAVE" are a point-in-time, I did two sets of readings using each balun and then took an average of just the POWER (measured in dBmV):

Code:
Channel     CM-3095     RS 15-1230      New Phillps     Old Phillips
-------     -------     ----------      -----------     ------------
8           -12.7       -12.3           -13.0           -13.5
9           -15.8       -15.9           -16.2           -15.9
11           -7.8        -8.0            -8.5            -8.0
12          -24.5       -24.3           -24.7           -24.8

Last edited by re_nelson; 2011-01-29 at 06:44 PM. Reason: Cited post number for previous data set
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post #659 of 827 (permalink) Old 2011-01-30, 08:24 AM
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+/- a dB between baluns.
Looks like no impact
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post #660 of 827 (permalink) Old 2011-01-31, 02:01 PM
 
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Comparison of four commercially available 300/75 ohm matching transformers (balu

Two each of the test baluns were purchased from an online seller of TV accessories. The subject baluns were tested for insertion loss using the conventional back-to-back method utilizing an HP8569B/8444 combination. Each balun pair was installed into the same fixture (a DB2/4 balun box) so that there would be no difference in the layout of the 300 ohm side of the baluns. Each pair was swept from 50 to 1,000 MHz and the resulting plots were overlaid on a grid representing the scope's graticule. The scope's text display and a legend was added.

Each graph represents the frequency response of a PAIR of baluns. If each device of the pair were identical, the insertion loss of a single device would be half the measured value of the pair. Since there are variations in devices, this should be accepted only as a genera idea of how each device performed, but, due to the lack of a significant sample size, should NOT be extrapolated to the larger population of devices under the same model number from the same manufacturer. A much larger sample would be needed to identify any trends. Anyone who publicly attempts to make a reach based on this limited data set will be severely chastised.

Reading the plots

The center horizontal line is the 0 dB reference. Each additional line below the middle line represents 2 dB of insertion loss at an given frequency. The center vertical line represents a frequency of 500 MHz. Each vertical line one both side of this line represents 100 MHz difference in frequency. Therefore, from the left, the first vertical line after the border represents 100 MHz, the second 200 MHz, and so forth. Anything under 50 MHz as shown on the plot should be ignored as it is below the operating range of the equipment and there will be anomalies in that part of the graph.

Keep in mind that the equipment used is only able to represent the baluns' response as a scalar value. It is not able to measure complex values related to phase or impedance variations.





As a comparison, ten pairs of the balun/PCB that we use in the C5 were tested and the results are shown below. This balun was selected for superior high-VHF response with as good of UHF response as we can get. They are hand-assembled, so there is definitely some variability in the batch that is apparent in the UHF band.



Discussion is now welcome!

Last edited by ADTech; 2011-01-31 at 06:43 PM. Reason: Added description
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