Signal Amplifiers (Amps, Preamps, Distro Amps)

Pete:

Thanks for your detailed posts about your adventures with overload; I found them very interesting. I saw your partial tvfool report link and looked at it to see how strong your local signals are:
http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id%3d1dda169109ca5c

KVCR at -15.6 dBm is a challenge to weak signal reception. I have been helping Ynot713 on another forum (not allowed to link to it) with a similar problem. His strongest signal is -10.4 dBm (highlighted in red), and I suggested that a drop amp might work for him as it has for you. I also gave him the link to ADTech's SA images.
http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id%3d1ddae813d84d07

Once I’m cleared to post attachments, I’ll attach a drawing of my system.

Click to expand...

You are not able to post attachments on this forum unless you are a supporter, but you can include an image (use BB Code) of your diagram in your post, or link to an image host. You mentioned a link to your diagram in post #3334, but I don't see a link.

I looked at your album and saw a thumbnail image, but the fullsize image is missing. That has happened to other forum members too, including me. Are you able to upload the image of your diagram again?

How to create a photo album for use on the Digital Forum
http://www.digitalhome.ca/forum/showthread.php?t=92167

Post Pic or attachments
http://www.digitalhome.ca/forum/showthread.php?t=132164
and in particular
http://www.digitalhome.ca/forum/showpost.php?p=1177653&postcount=11

Looking forward to seeing your diagram.

Pete:

Thanks for the PM and for uploading the image. I didn't see the image in 3334 at first, but when I used the link in your text box without the IMG brackets in a separate window, I was able to recover the image. After that, it showed in your 3334 post and your album.

After your update, it didn't show in your post or your album, only 7 images as before.

Anyway, I have the image which is, as you said, moderately clear @ 94.9KB(600x777) which is good enough for me to figure out the power feeds for the drop amps which interested me. I have a 3410 and a 3412 and plan to use them with PCT-MPI-1G power inserters if I can find them. If not, maybe a different brand will work.

When I was trying to recover the image, I tried different forum styles with the Quick Style Chooser at the bottom of the frame and it seemed to make a difference. I tried it again, and it didn't; it was just a coincidence that I was doing it at the same time you were in your album.

I'm tempted to post it as an attachment, but I wouldn't do it without your permission. If it shows up full size in your album, that would be sufficient.

I see that you are also a ham; that's why you know what you are doing!

Thanks again for the information about your impressive setup.

Best regards,
rabbit

Rabbit73,

The PCT MA2-M’s are rated @ 15 VDC, 300 ma. They measure 2 ¼” X 3 3/8” and only weigh 4 5/8 oz. They can be powered through the RF output port (via a power inserter) or through a separate power input port (adjacent to the RF IN port). I have two of them mounted directly on the antennas with F-71 M-M barrel connectors.

I have 125’ of RG-6 between my power source and the amps., so I was expecting some voltage drop across the coax. Plus I wanted to combine two antennas with minimal loss and couldn’t find a UVSJ that would pass power on both ports.

I decided to build a couple of power distribution boxes and fit them with fixed +15V, 1.5 amp. 3-terminal 7815 regulators. The regulators are bypassed on the input with 0.33uF caps and on the output with 0.1 uF caps. I used a leftover Laptop power supply that outputs 20 VDC @ 2.5 amps. The regulators and chassis mount ‘F’ connectors are mounted on an aluminum plate inside a plastic box that 22 cartridges came in. Voltage drop across the 125’ of coax is well below the regulation minimum. Hope this helps clarify the small print on the pictorial.

Pete:

I see the full size image in your album now, but it doesn't show in post 3334. The image that I recovered was the old one with pictureid=6018. The new image is pictureid=6098, so I don't think it will show in post 3334. Maybe you can PM the moderator and ask him to edit the link from 6018 to 6098. Or maybe, using 20-20 hindsight, I should have suggested that you ask to have 6018 removed from quarantine.

Thanks for telling me about your experience with alternate power inserters; I'll keep that in mind.

With 125 ft of RG6, I understand why you put the 7815s up by the antennas, expecially if the coax is CCS instead of solid copper. With reduced voltage the amps might not perform as well as far as IM products and NF are concerned.

Yes, I am a ham. I asked the rabbit and he said he didn't want to trade his username for a callsign in a public forum; he's laying low and hiding from the FOX!
He did say I could do this:

Thanks and 73 from
W4...
ex-W2...
ex-DL4.. US Army radio operator, Germany, 1955

Pete's Diagram

Here is a higher resolution file of Pete's diagram that he was kind enough to send to me. I am using my image host because it allows a larger file size and larger image size to see the detail:



If above link fails, you can view the diagram at a lower resolution in Pete Higgins album.

And just for fun, I used Auto Sharpen in Adobe Photoshop Elements 6.0 to make it a little better, but the file size is a little larger. This is the link to that image:

http://i496.photobucket.com/albums/rr328/rabbit73_photos/PeteDiag3_zpsb2e3fdc1.jpg

Problems in Markham

I have had this discussion on the ganging antennas thread looking for answers. Roger1818 has had some suggestions but none have worked out so I thought I would see if anyone here has some thoughts. I have pasted my description of the problem.

OK guys I appreciate the input. Here is another thing I discovered today. A little history. CFTO reception problems began last summer. I put it down to trees or the change to VHF even though it was ok when the change first happened. The in the late fall I lost all US stations on my upstairs Samsung set. My basement Sony was fine except for CFTO. I discovered if I backed the antenna connector slightly out of the Samsung my US stations came back. I put this down to either a failing tuner or bad connection inside. I purchased another Sony set at Christmas and replaced the Samsung with the Sony from downstairs. Everything was fine except for no CFTO. About 6 weeks ago I lost Fox on both sets. Today I was playing around and decide to try an attenuator. While disconnecting things as I back out the antenna connection on comes Fox at full strength! I attach the attenuator and everything seems fine. NO CFTO. I check downstairs and have lost almost all my stations. Remove the attenuator upstairs and on they all come both upstairs and downstairs. The Fox downstairs starts to fade and backing the connection out slightly brings it back. It would appear I have some sort of fluctuating signal affecting the tuners on both sets and the only thing I can come up with is a failing preamp. OH and also once I fiddle and get Fox I have no sign of CFTO at all. If I tighten things up no Fox but a flickering of CFTO. No lock though. Crazy. I am feeling now the antenna and its aim are not the problem. I am baffled and frustrated to say the least. Any thoughts are much appreciated. Mods feel free to move this if it is in the wrong thread.

I have checked the connections inside and they seem fine. I changed the connection on the power injector that runs to the splitter. While doing this I got the fluctuating signal strength on Fox that I get when I disconnect the antenna at the tv sets. If I unplug the power injector I lose all stations, as you would expect. Plug it back in and everything is fine. EXCEPT CFTO and WUTV.My feeling is this is not an aiming issue as I can get these channels by playing around with the connections, at normal strengths, but they are quickly gone again. Does the fact that CFTO is 9.1 and Fox 14.1 have anything to do with this? ie the higher up you go the less influence whatever problem is going on would have? I will check the voltage at the injector but if it isn't high enough could the pre amp run moderately well but not well enough for these channels? And why would wiggling the connection only affect these 2 channels. I still feel this may well be a preamp problem as it seems to be a powered set of circumstances that cause things. I found a new power injector on line but it is about $45.00 by the time I get it. I wondered if this turns out to be the problem if I should just get a new preamp. If so which one? I know the new CM7778 is not highly thought of and the AD CPA19 doesn't seem to be readily available anymore.

My setup is a chimney mounted original CM4221 and original CM7778.

Thanks for any ideas.

Bman72s:

Your problem sounds difficult and frustrating. I looked at a few of your previous posts. This might be the proper thread because it sounds like a preamp problem.

I couldn't find a link to your tvfool report. Does it look something like this?

http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id%3d1dda06c6668210

How is you 4221 connected to the 7778?

Is your power supply/power injector the CM 0747?

A diagram of your system would be helpful, showing what is connected to what.

Hi Rabbit/Roger
For some reason TV fool won't accept my address this morning but yes that is fairly representative. The power injecter is the cm 0747. Following is an idea of my set up.

CM4221 chimney mount.
Cm7778 preamp on mast just below CM4221
Cable down chimney to grounding block - 25feet?
Cable to inside basement to power injector-20 feet
Cable out of injector to 2 way splitter-3 feet
Cable to downstairs tv out of splitter-3 feet
Cable to upstairs tv out of splitter- 75 feet

Last night everything ran well with WUTV at almost full strength and CFTO locked at 50%. Other US and Canadian stations as usual. 2 or 3 hours later WUTV starts to drop off and signal strength fluctuates wildly between 0 and 90% CFTO starts to drop. All others normal. It is those 2 stations that are the main issue. The reason I keep going back to the pre amp is, because it happens on both sets I feel it is a common problem. Therefore I think it is either the connection at the antenna,connection at grounding block, splitter ( I just replaced it) or preamp. Because it is ok sometimes and then as time passes starts to fail I am leaning towards the pre amp and maybe a failing power supply. ie it is ok for a while but not for long. I feel all my other stations would be problematic if it was bad connections. What I don't understand is why it seems to only affect those 2 stations. The only thing I could come up with is CFTO broadcasts on 9.1 and WUTV on 14.1 and they are closest to each other. I don't even know if that is a viable reason. Up until the start of all this WUTV would have been one of my most reliable US stations and CFTO was of course a flame thrower. The change to VHF affected CFTO but I had no problems with it until last summer. To be honest I don't remember what my strength reading were after the change but they weren't enough to cause any issues for quite a while. It seems to me CFTO changed to VHF in maybe the summer of 2011? Up until this issue the set up had been quite reliable with only weather related reception issues or the odd minimal tweak in antenna aim. Nothing in the set up has changed since the initial install. Meanwhile I watch on Bell TV until I find this problem or rip it all down in frustration. As much as I like OTA this is the reason I would never cancel my other service. Things do happen.

Some ideas to try

Bman72s

I have just enough (outdated) expertise to be dangerous, plus I am paranoid about signal overload, plus I obviously don’t proficiently speak Canadian… so it took me awhile to figure out what you meant by “CFTO”, but I'll try to help.

As I'm sure you know, your 4221 antenna is a 4-Bay Bow Tie designed for UHF reception. CFTO is broadcast on VHF channel 9 @ only 17.4 kW of power. It also comes from ~43 deg. off bore sight from the Baltimore (Fox) stations. One source of your trouble with CFTO could be that a combination of propagation anomalies and antenna pointing are responsible for your degrading reception over time although I would expect CFTO to appear randomly good or bad. A solution to that would be the addition of a High VHF antenna such as an Antennacraft Y5-7-13 or Y10-7-13 and aiming it towards the Toronto station, then optimizing your 4221 for Baltimore. If your “original” amp has a single RF input, you would also need a UHF-VHF Band Separator/Combiner (UVSJ).

What you describe could also be a milder case of what I experienced with my OTA project. Because of the intermittent nature, I first suspected bad cable connections or parts. I replaced an existing ~30 year old; 125’ run of RG-6 with brand new RG-6, fitted with new Channel Master compression connectors. I substituted both the antenna to pre-amp balum and its jumpers and tried different pre-amps. Sometimes it would work pretty good, at other times it was flaky as all get out.

The 7778 pre-amps are excellent in weak signal environments but lack the “head-room” to tolerate moderate to strong signal environments. Antenna pre-amps are designed to amplify signals within their “linear” range. When input signal strengths exceed that range Inter Modulation Distortion (IMD) products are produced. IMD products are mathematical sums, differences and multiples of the signals involved. If your 7778 is being hit by strong signals causing gain compression or whose IMD products fall on CFTO then that could explain your erratic reception.

To test for this, remove the amplifier and power inserter from your lead-in and see if the CFTO signal can be received reliably (if at all). If it is received but variations still occur then some other mechanism is at work, probably multi-path. 50 years ago we used to get this near Lindberg field as the signals reflected off the arriving & departing airplanes.

If you can’t receive CFTO without a pre-amplifier, try holl_ands trick of using 3 – 6 dB attenuation between the antenna and the pre-amp input. Again, if the degradation is eliminated it is indicative of 7778 overload, if not, it’s some other mechanism.

Obviously, while your making these changes, re-check for loose connections or intermittent cables but they would typically affect all channels.

Partially removing the coax from your TV should reduce the signal strength. One last thought is that your 7778 has to much gain and is slightly over driving your TV tuner. Since most modern tuners are designed to work with relatively strong cable channels, and you've tried two different TV's I doubt that that is the case, but it wouldn't hurt to try your attenuators @ the TV input if my other suggestions don't work.

Please let us know what you find.

Rabbit I can now get my tv fool report so it must have been a website problem. I had looked at it many times before this morning so I was wondering why it hadn't worked. How do I post it to the site?

Pete THANK YOU for your insight. You might be on the right track. I tried a 3 db attenuator upstairs and downstairs with no improvement. However one time by installing it upstairs ALL channels were missing downstairs but removing it upstairs brought them back. I detailed this in the ganging thread when I thought I was dealing with an antenna problem. Are you saying to place an attenuator between the antenna line and input to the power supply? haven't done that. I had thought of bypassing the pre amp so as soon as it warms up here I will go up on the roof and bypass it and check the aim. Thanks for your suggestions. By the way my Fox station is from Buffalo not Baltimore. I would be some impressed if I was getting Baltimore here even with all the drop outs and stuttering. LOL

MapMaker

If the problem isn't there both TVs act the same. Once it surfaces both sets are the same. The only difference is my snr readings on the new downstairs set are approximately 2 to 3 less than upstairs. However it locks at a lower reading than the upstairs one. Interestingly they are both Sonys. I feel it has to be in the system not the TVs but I understand your thoughts re warming up.

Thanks to all of you for your input. I am on a mission to figure this out before my Wife kills me for spending so much time on it. LOL