Ideas on how to turn a UHF antenna into a UHF/VHF antenna. - AVS Forum
Forum Jump: 
Reply
 
Thread Tools
post #1 of 52 Old 06-13-2009, 05:10 PM - Thread Starter
Member
 
fcondron's Avatar
 
Join Date: May 2005
Location: SE Michigan
Posts: 46
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
I've been chugging along great for a few years now, picking up OTA HD broadcasts in my area on a DB4 that I have sitting in a second-floor bedroom. With the digital transition, one of my main stations (the local Fox affiliate, WJBK) switched over to a VHF channel - 7. So, now I'm not receiving them (though I've read some with DB4's are picking them up, perhaps they're closer).

When I look up my address on antennaweb, all the stations I care about are broadcasting from about 19 miles away, at close to the same angle (varies from 52 degrees to 72 degrees).

Any recommendations on a VHF-only antenna I can mix in with my DB4, or an antenna that handles both VHF and UHF to replace it? I'd prefer to keep it indoors if possible, as that's the easiest solution for me. Does something like the Winegard MS-2000 sound like it would work in this situation?

Thanks in advance,

-Frank
fcondron is offline  
Sponsored Links
Advertisement
 
post #2 of 52 Old 06-13-2009, 06:43 PM
 
serndipity's Avatar
 
Join Date: Apr 2007
Location: Marblehead
Posts: 172
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
I had three stations switch back to VHF (7, 9 and 11).

The two DIY UHF antennas, a C2 clone and a 7 element LPDA (log periodic dipole array), that I have been using would not pick them up.

I made a simple modification to each and viola, can receive all three VHF stations with no problems (35 - 50 miles distant, line of sight, antennas in attic 45' above ground).

On the C2 clone. I added a VHF (high) dipole at the junction of the 2 loops.

On the LPDA, I added extensions to the rear element, such that was now a VHF (high) dipole.

In both cases, the UHF performance did not suffer.

Try this on your DB4.

Add a ch 7 dipole to the center of your DB4 (where the feed line attaches). Each side of the dipole will be 16" - 17". You can easy try this with two pieces of wire and alligator clips.
serndipity is offline  
post #3 of 52 Old 06-14-2009, 01:13 PM - Thread Starter
Member
 
fcondron's Avatar
 
Join Date: May 2005
Location: SE Michigan
Posts: 46
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Thanks for the tip! I had some spare 220v electrical cable, so I cut out 17" lengths of the copper wire from it, soldered each one to an alligator clip, and clipped it on to the bolts on the DB4 that connect the coax adapter to the antenna itself.

I was immediately able to scan that missing channel, though only with about 16% signal strength. Lots of dropouts. Of course, these lengths were now 17"+length of alligator clip, so I started cutting off quarter-inch lengths and watching the signal strength. I've managed to grow it up to where it's bouncing between 54-70% (all my other UFH channels are coming it at 87-98%) on a beautiful clear day.

Any more tips to improve it even more?

Here's how it looks now:


-Frank
fcondron is offline  
post #4 of 52 Old 06-14-2009, 01:32 PM
Advanced Member
 
johnpost's Avatar
 
Join Date: Mar 2008
Posts: 783
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by fcondron View Post

I cut out 17" lengths of the copper wire from it, soldered each one to an alligator clip, and clipped it on to the bolts on the DB4 that connect the coax adapter to the antenna itself.

Any more tips to improve it even more?

yes get a new piece of wire and screw it under the bolts or put the wire in a spade or ring lug and attach it to the bolts. retune the antenna. clips are poor contact especially over time.
johnpost is offline  
post #5 of 52 Old 06-14-2009, 02:23 PM
Member
 
topp's Avatar
 
Join Date: Dec 2003
Posts: 99
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 3 Post(s)
Liked: 10
I am in a similar situation where I lost some of my channels because they switched to VHF. However, I have the older stile Channel Master 4221 4-Bay antenna. Is there modification I can do to pick the VHF channel back up or should I just buy a new antenna?

Thanks,
Topp
topp is online now  
post #6 of 52 Old 06-15-2009, 01:17 PM
Member
 
dpstrand's Avatar
 
Join Date: Jan 2007
Posts: 85
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
I have a DB4 in Huntington Beach, CA and lost all the now VHF channels (7,9,11,13). I am about 38 miles from the transmitters with line of sight on all of them. Here is my tvfool link: http://www.tvfool.com/?option=com_wr...663dfc20f6a4ab

Is this modification likely to work ok, or am I going to need to pick up a new antenna? The antenna is roof mounted but needs to stay small (DB4 sized). I was debating trying the winegard HD-1080, would that be a good choice?
dpstrand is offline  
post #7 of 52 Old 06-15-2009, 03:27 PM
Senior Member
 
Don_M's Avatar
 
Join Date: Mar 2008
Location: SW Aurora, CO
Posts: 475
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
topp and dbstrand, you'd both be better off adding a VHF-high antenna such as an AntennaCraft Y5-7-13 (inexpensive, traditional form factor, decent performance) or an Antennas Direct C5 (cool looking, likely similar performance, expensive) to your current antennas. The Y5 needs a coax matching transformer; the C5 doesn't. A UVSJ combiner will merge the cables from each antenna into a single downlead. Together, these antennas will perform much better than an HD-1080. The 1080 isn't in the same league on UHF as the CM 4221 or DB-4 and its VHF performance is, frankly, poor.
Don_M is offline  
post #8 of 52 Old 06-15-2009, 04:14 PM
Senior Member
 
rschneider's Avatar
 
Join Date: Dec 2000
Location: Wildwood, MO
Posts: 387
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
fcondron,

I haven't posted here in years, but I had to reply to this post.

Thanks for the picture I sent this to our engineers and they got a kick out of it!

I'm glad it’s working out for you, unfortunately in antenna design when you add performance in one area you will likely lose it elsewhere. We have looked at dozens of different scenarios to add VHF elements to the Bowtie antennas and the results were significant performance penalties somewhere in the UHF band.

To compound issues even more we have heard from station engineers that the ERP of many of the DTV stations reverting back to VHF have been cut significantly. This can make a difficult situation nearly impossible.



So for others having problems with VHF reception on their bowtie antennas we suggest two options.

First
If you have an older bowtie antenna such as the one pictured by fcondron, we will replace the old ferrite core balun with a new PCB balun. These offer much better high VHF capabilities since (in addition to being more efficient) it has the effect of turning the coax shielding in to a VHF radiator.

It’s not a magic bullet, but should give you 10-20 miles of range on high VHF (provided the station isn't broadcasting to the parking lot.) We have been using the PCB balun for about 2 1/2 years.

I have about 100 extra in the shop, we will send these out to previous customers no charge, just email: info@antennasdirect.com to request one.

Second:
If that doesn’t work then the other option is a two antenna solution, such as the Antennacraft, Winegard or our Clearstream 5 coupled with a UHF/VHF diplexer (DO NOT use a reversed splitter to combine antennas!)

Our C5 will begin shipping tomorrow and may be the more expensive option ($119) since the miter joints on the square tube aluminum must welded by hand. It is extremely efficient and compact for a VHF design. Our competitors make good antennas as well so I won’t launch into a commercial for our product on this forum.

I hope this helps


Richard Schneider

Antennas Direct.
rschneider is offline  
post #9 of 52 Old 06-15-2009, 04:28 PM
AVS Addicted Member
 
Ken H's Avatar
 
Join Date: Nov 1999
Location: Metro Detroit
Posts: 45,876
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 12
Topic title edited.

'Better Living Through Modern, Expensive, Electronic Devices'

Ken H is offline  
post #10 of 52 Old 06-15-2009, 05:04 PM - Thread Starter
Member
 
fcondron's Avatar
 
Join Date: May 2005
Location: SE Michigan
Posts: 46
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by rschneider View Post

fcondron,

I haven't posted here in years, but I had to reply to this post.

Thanks for the picture I sent this to our engineers and they got a kick out of it!

First
If you have an older bowtie antenna such as the one pictured by fcondron, we will replace the old ferrite core balun with a new PCB balun. These offer much better high VHF capabilities since (in addition to being more efficient) it has the effect of turning the coax shielding in to a VHF radiator.

It's not a magic bullet, but should give you 10-20 miles of range on high VHF (provided the station isn't broadcasting to the parking lot.) We have been using the PCB balun for about 2 1/2 years.

I have about 100 extra in the shop, we will send these out to previous customers no charge, just email: info@antennasdirect.com to request one.


Richard Schneider

Antennas Direct.


Thanks, I'll take you up on that offer for the new balun. Email sent.

I looked at and drooled over the C5, but thought I'd try this quick-dirty homemade solution.

-Frank
fcondron is offline  
post #11 of 52 Old 06-15-2009, 07:22 PM
Advanced Member
 
mclapp's Avatar
 
Join Date: Apr 2008
Location: Delaware Co. ,NY
Posts: 717
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by topp View Post

I am in a similar situation where I lost some of my channels because they switched to VHF. However, I have the older stile Channel Master 4221 4-Bay antenna. Is there modification I can do to pick the VHF channel back up or should I just buy a new antenna?

Thanks,
Topp

Add some extensions to the screen of the 4221 or attach some pieces of metal to the back of the screen. You'll need to end up with 32" wide or more for the reflector only 4 to 8 extensions or rods are needed. I did some tests on an old style 4221 using both screen and some threaded rods attached to the back of the original screen and it made a lot of improvement on many VHF-HI channels.

The plot below shows the results, it still doesn't match the homemade versions with longer whiskers but still is better than nothing


I dont see any reason why the db4 wouldn't also benefit from this modification as well.
mclapp is offline  
post #12 of 52 Old 06-15-2009, 10:22 PM
Member
 
dpstrand's Avatar
 
Join Date: Jan 2007
Posts: 85
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Thanks for the reply rschneider. How can we determine if we have the old balun or the new pcb design?
dpstrand is offline  
post #13 of 52 Old 06-15-2009, 10:35 PM
AVS Special Member
 
EscapeVelocity's Avatar
 
Join Date: Nov 2006
Location: Charleston, SC
Posts: 5,639
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 106 Post(s)
Liked: 111
You can add a VHF Rabbit Ear Dipole to your DB4 using a UVSJ combiner. Like the Channel Master 4000 or the Philips MANT075 or homemade. That will keep the VHF dipoles from screwing with your UHF signals from the DB4.

Vizio VP322 Plasma / Vizio GV42LF LCD / Denon 2200 Silicon Image DVD / Panasonic S97 Faroudja Genesis DVD / Oppo 970HD Mediatek DVD / Oppo 983H Anchor Bay DVD / Panasonic LX-600 Laserdisc / Aiwa MX100 Multi-region VCR / JVC S7600 S-VHS / PS2 / Sega Genesis / Nintendo SNES / Roku 2 XS & HD-XR / Realistic STA-90 Reciever / Realistic Minimus 7 / Antennacraft G1483 Hoverman / Belden 7915A RG6 / Channel Master 7777 Titan 2 UHF/VHF / Panasonic AX-200u / Optoma Graywolf 92" / Draper Luma 92"
EscapeVelocity is offline  
post #14 of 52 Old 06-15-2009, 10:40 PM
AVS Special Member
 
EscapeVelocity's Avatar
 
Join Date: Nov 2006
Location: Charleston, SC
Posts: 5,639
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 106 Post(s)
Liked: 111
Hello rscheider, I have a C1C that I am testing right now and am getting some VHF performance out of it....even at 45 miles flat land but no LOS and on channel 7....its not dependable but I was surprised.

I would like to commend your recent antenna designs.....and beg you to put out a Gray Hoverman tuned to the new spectrum, as it offers some VHF performance to speak of.....but with quality materials like your DB2 and DB4. AntennaCraft had one but its quality leaves much to be desired. Also the 4 bay design has been tuned by mclapp to give better performance on VHF Hi and tuned to the new UHF spectrum, you may want to check out.....longer whiskers and wider element spacing center to center on the bowties than the DB2.

Vizio VP322 Plasma / Vizio GV42LF LCD / Denon 2200 Silicon Image DVD / Panasonic S97 Faroudja Genesis DVD / Oppo 970HD Mediatek DVD / Oppo 983H Anchor Bay DVD / Panasonic LX-600 Laserdisc / Aiwa MX100 Multi-region VCR / JVC S7600 S-VHS / PS2 / Sega Genesis / Nintendo SNES / Roku 2 XS & HD-XR / Realistic STA-90 Reciever / Realistic Minimus 7 / Antennacraft G1483 Hoverman / Belden 7915A RG6 / Channel Master 7777 Titan 2 UHF/VHF / Panasonic AX-200u / Optoma Graywolf 92" / Draper Luma 92"
EscapeVelocity is offline  
post #15 of 52 Old 06-16-2009, 01:43 PM
Senior Member
 
rbarbier's Avatar
 
Join Date: Nov 2004
Location: Perris, CA.
Posts: 215
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by rschneider View Post

fcondron,

I haven't posted here in years, but I had to reply to this post.

Thanks for the picture I sent this to our engineers and they got a kick out of it!

I'm glad it’s working out for you, unfortunately in antenna design when you add performance in one area you will likely lose it elsewhere. We have looked at dozens of different scenarios to add VHF elements to the Bowtie antennas and the results were significant performance penalties somewhere in the UHF band.

To compound issues even more we have heard from station engineers that the ERP of many of the DTV stations reverting back to VHF have been cut significantly. This can make a difficult situation nearly impossible.



So for others having problems with VHF reception on their bowtie antennas we suggest two options.

First
If you have an older bowtie antenna such as the one pictured by fcondron, we will replace the old ferrite core balun with a new PCB balun. These offer much better high VHF capabilities since (in addition to being more efficient) it has the effect of turning the coax shielding in to a VHF radiator.

It’s not a magic bullet, but should give you 10-20 miles of range on high VHF (provided the station isn't broadcasting to the parking lot.) We have been using the PCB balun for about 2 1/2 years.

I have about 100 extra in the shop, we will send these out to previous customers no charge, just email: info@antennasdirect.com to request one.

Second:
If that doesn’t work then the other option is a two antenna solution, such as the Antennacraft, Winegard or our Clearstream 5 coupled with a UHF/VHF diplexer (DO NOT use a reversed splitter to combine antennas!)

Our C5 will begin shipping tomorrow and may be the more expensive option ($119) since the miter joints on the square tube aluminum must welded by hand. It is extremely efficient and compact for a VHF design. Our competitors make good antennas as well so I won’t launch into a commercial for our product on this forum.

I hope this helps


Richard Schneider

Antennas Direct.

Richard,

I would like to buy the C5 (I have the C4 already that does great with UHF but doesn't pick up 7-13). Where is it available.

Do you think the C5 with the C4 will work for me? I have a Channelmaster 7777 Pre-amp with it. (I want 7, 9, 11, and 13).

http://www.tvfool.com/?option=com_wr...663d23d52b0c16

www.thegamefan.com

Proud owner of 3 HD DVD players and 170+ HD DVD movies.
rbarbier is offline  
post #16 of 52 Old 06-17-2009, 07:16 AM
Member
 
sggoodri's Avatar
 
Join Date: Jan 2008
Location: Cary, NC
Posts: 134
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
My preamp has separate inputs for VHF and UHF. Currently I'm using only the UHF input with my CM4228, mounted in my attic, yet I still get VHF high fairly well for a nearby station (11) in front of it. But I'd like to make it stronger.

If I add a separate VHF antenna how far away from my CM4228 should I mount it? How far laterally (in attic) versus above or below?
sggoodri is offline  
post #17 of 52 Old 06-17-2009, 10:51 AM
AVS Special Member
 
Phantom Gremlin's Avatar
 
Join Date: Aug 2002
Location: Tualatin Oregon
Posts: 1,407
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by rschneider View Post

Our C5 will begin shipping tomorrow and may be the more expensive option ($119) since the miter joints on the square tube aluminum must welded by hand. It is extremely efficient and compact for a VHF design.

What am I missing? Why don't you offer a compact antenna like the C5 but also including UHF? Isn't that an obvious product? Right now I'm using a Silver Sensor and my high VHF works but signal strength is a little low. I don't want problems during rainstorms. Using a Silver Sensor plus C5 plus a UVSJ combiner just screams kludge. I can't be the only potential customer with this problem!
Phantom Gremlin is offline  
post #18 of 52 Old 06-17-2009, 12:53 PM
AVS Special Member
 
blue_z's Avatar
 
Join Date: Feb 2006
Location: So Cal
Posts: 1,026
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 18
Quote:
Originally Posted by sggoodri View Post

My preamp has separate inputs for VHF and UHF. Currently I'm using only the UHF input with my CM4228, mounted in my attic, yet I still get VHF high fairly well for a nearby station (11) in front of it. But I'd like to make it stronger.

Of the 4 VHF channels in LA, 11.1 does seem to be the weakest for the 4228 8-bay. I also have the 4228 in the attic. The PCI tuner on the 2nd floor receives all channels with "signal strength" above 90. But the 1st floor tuner has problems with 11.1. Note that this is with a 2-way splitter and no amplification. The extra 20 feet of (old) RG-6 is enough to teeter at the "digital cliff".

Rather than another antenna, why not test without the preamp (which could be acting as a filter), or replace that preamp with a wideband unit. The 4228 seems to have enough gain to make a VHF-hi antenna unnecessary.

Also make sure that the two screen halves are in contact with each other. If necessary use a few nylon cable ties to join then. Apparently it's the wide horizontal wires of the screen that contribute to the VHF gain.
blue_z is offline  
post #19 of 52 Old 06-17-2009, 04:10 PM
Member
 
wallybarthman's Avatar
 
Join Date: Apr 2007
Posts: 182
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by rbarbier View Post

Richard,

I would like to buy the C5 (I have the C4 already that does great with UHF but doesn't pick up 7-13). Where is it available.

Do you think the C5 with the C4 will work for me? I have a Channelmaster 7777 Pre-amp with it. (I want 7, 9, 11, and 13).

http://www.tvfool.com/?option=com_wr...663d23d52b0c16

I'm wondering about the same possible configuration.
wallybarthman is offline  
post #20 of 52 Old 06-17-2009, 05:09 PM
AVS Special Member
 
blue_z's Avatar
 
Join Date: Feb 2006
Location: So Cal
Posts: 1,026
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 18
Has anyone tried using 300-ohm twinlead for a folded dipole?

http://www.wfu.edu/~matthews/misc/dipole.html
blue_z is offline  
post #21 of 52 Old 06-17-2009, 06:27 PM
AVS Special Member
 
ProjectSHO89's Avatar
 
Join Date: Feb 2009
Posts: 2,534
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 22 Post(s)
Liked: 60
Quote:
Originally Posted by Phantom Gremlin View Post

What am I missing? Why don't you offer a compact antenna like the C5 but also including UHF? Isn't that an obvious product? Right now I'm using a Silver Sensor and my high VHF works but signal strength is a little low. I don't want problems during rainstorms. Using a Silver Sensor plus C5 plus a UVSJ combiner just screams kludge. I can't be the only potential customer with this problem!

See the design engineer's comments at http://www.digitalhome.ca/forum/show...rstream&page=8

Your exact question is answered by him in that discussion.
ProjectSHO89 is offline  
post #22 of 52 Old 06-17-2009, 07:14 PM
Advanced Member
 
johnpost's Avatar
 
Join Date: Mar 2008
Posts: 783
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by blue_z View Post

Has anyone tried using 300-ohm twinlead for a folded dipole?

http://www.wfu.edu/~matthews/misc/dipole.html

it works good if you have a strong tv signal and want a single channel.

same design makes a good antenna for FM radio
johnpost is offline  
post #23 of 52 Old 06-18-2009, 05:45 AM
AVS Special Member
 
holl_ands's Avatar
 
Join Date: Jun 2004
Location: San Diego, CA
Posts: 3,591
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 18 Post(s)
Liked: 52
I ran NEC Sim for Folded Dipole (using various wire diameters) to determine bandwidth.
Twinlead may or may not be adequate for Hi-VHF....the SWR and hence Net Gain are
degraded except on desired and adjacent channels.
AWG12 house wire is only slightly better....1/4 and 5/16-tubing don't quite cover Hi-VHF....
http://www.avsforum.com/avs-vb/showt...php?p=16657940
Note the importance of good SWR....

For Ch7-13, chop up a 10-ft length of 1/2-in diameter copper tubing (Type M) plus
four 90-deg elbows and a couple of BRASS bolts for about $10 (at HomeDepot):
http://pigtail.net/nicholas/ctn/dipole.html
Or if you're not into flux & solder, flatten the copper and simply bend it around,
saving $2 for the elbows:
http://www.homedepot.com/webapp/wcs/...ctId=100168538
http://www.homedepot.com/webapp/wcs/...ctId=100345671
plus a Balun:
http://www.summitsource.com/product_...oducts_id=6494
or RECYCLE something flat and wide...

And if you have the room, spend another $7 and add at least a Reflector.....
And maybe a Director....At which point we can say, "Welcome to Yagiville".....

FYI: Net Gain and SWR charts for CH6 (plus CH5 & FM Band) are attached.
SWR should be no more than about 2 and preferably 1.5....although some
wide band TV antennas extend as high as (ouch!) 3.
LL
LL
holl_ands is offline  
post #24 of 52 Old 06-25-2009, 07:31 AM - Thread Starter
Member
 
fcondron's Avatar
 
Join Date: May 2005
Location: SE Michigan
Posts: 46
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by fcondron View Post

Thanks, I'll take you up on that offer for the new balun. Email sent.

I looked at and drooled over the C5, but thought I'd try this quick-dirty homemade solution.

I received the new balun for my DB4 from Antennas Direct - thanks!

I installed it - now I can pick up VHF channel 7. It's not perfect - my UHF channels all come in at 87-98%, while this VHF channel is coming in at 54%, but it is certainly a major improvement over the old balun.

-Frank
fcondron is offline  
post #25 of 52 Old 06-26-2009, 06:53 AM
Advanced Member
 
Rick313's Avatar
 
Join Date: May 2008
Location: Lone Tree, CO
Posts: 525
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 11
Quote:
Originally Posted by mclapp View Post

Add some extensions to the screen of the 4221 or attach some pieces of metal to the back of the screen. You'll need to end up with 32" wide or more for the reflector only 4 to 8 extensions or rods are needed. I did some tests on an old style 4221 using both screen and some threaded rods attached to the back of the original screen and it made a lot of improvement on many VHF-HI channels.

I have a DB4 and am considering adding some rods to the reflector in an attempt to improve VHF reception, but I have the following questions:

1. How does the spacing work? Do the rods need to be a certain distance from one another? Do they go between the bowties or directly behind them?

2. What is the impact of using 4 versus 8 rods?

3. What material do you recommend for the rods?
Rick313 is offline  
post #26 of 52 Old 06-26-2009, 01:23 PM
Advanced Member
 
mclapp's Avatar
 
Join Date: Apr 2008
Location: Delaware Co. ,NY
Posts: 717
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by Rick313 View Post


1. How does the spacing work? Do the rods need to be a certain distance from one another? Do they go between the bowties or directly behind them?

Centered directly behind each bay (set of whiskers) if using only 4.
Quote:
2. What is the impact of using 4 versus 8 rods?

8 gives better rear rejection and slightly improves some UHF channels. If using 8 space them 4" apart centered behind each set of whiskers.
Quote:
3. What material do you recommend for the rods?

Anything metal, round, flat, solid, hollow, whatever, larger diameter pieces will allow you to use less rods and still get good rear rejection. If you use small diameter like wire you'll be better off using 8 elements or extensions. If you use extensions you must make sure that they make solid electrical contact with the exsisting screen.

I did a test using 1/4" threaded rods and 2"x4" wire fencing and attached each to the back of the original screen and both worked well for VHF-Hi behind a CM4221.

This mod won't make a great VHF performer out of a 4 bay but it will make a difference compared to the un-modified version on most channels. I saw 5 - 10 db more forward gain compared to un-modified but it still had negative gain on some channels compared to a dipole.
mclapp is offline  
post #27 of 52 Old 06-27-2009, 07:44 AM
Member
 
rgharrin's Avatar
 
Join Date: Oct 2004
Posts: 119
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Mclapp
Making the 4221 a better VHF antenna....does this apply to 4228?
If so, how can I improve channel 11?
rgharrin is offline  
post #28 of 52 Old 06-27-2009, 05:58 PM
Advanced Member
 
lexus2108's Avatar
 
Join Date: Mar 2008
Posts: 991
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by serndipity View Post

I had three stations switch back to VHF (7, 9 and 11).

The two DIY UHF antennas, a C2 clone and a 7 element LPDA (log periodic dipole array), that I have been using would not pick them up.

I made a simple modification to each and viola, can receive all three VHF stations with no problems (35 - 50 miles distant, line of sight, antennas in attic 45' above ground).

On the C2 clone. I added a VHF (high) dipole at the junction of the 2 loops.

On the LPDA, I added extensions to the rear element, such that was now a VHF (high) dipole.

In both cases, the UHF performance did not suffer.

Try this on your DB4.

Add a ch 7 dipole to the center of your DB4 (where the feed line attaches). Each side of the dipole will be 16" - 17". You can easy try this with two pieces of wire and alligator clips.

You have a pic of the C2 modification?
lexus2108 is offline  
post #29 of 52 Old 06-27-2009, 08:28 PM
Advanced Member
 
mclapp's Avatar
 
Join Date: Apr 2008
Location: Delaware Co. ,NY
Posts: 717
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by rgharrin View Post

Mclapp
Making the 4221 a better VHF antenna....does this apply to 4228?
If so, how can I improve channel 11?

The CM4228 has a wide enough reflector for VHF-hi if the screens are bound together to act as 1.

I don't have a 4228 to test but computer models show the 4228 to have some positive gain on most VHF-hi channels, especially the upper ones if the reflector screens are tied together.

The CM4221 has too narrow a factory reflector and it doesn't work as a reflector for VHF-hi. Making it wider 32" or more will make it a decent reflector for VHF-hi so that's the reason for the improvement with the 4221.

Neither antenna should be considered a serious VHF-hi antenna but with minor modifications they can be useable for many situations.
mclapp is offline  
post #30 of 52 Old 07-21-2009, 10:40 AM
Senior Member
 
rbarbier's Avatar
 
Join Date: Nov 2004
Location: Perris, CA.
Posts: 215
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Is there anyway in making my C4 into a High VHF/UHF antenna also? I get perfect UHF signals. Can't pick up the High VHF stuff in LA. I have tried the C5 and the Y57-13. With the C5 and the Y5 7-13, I was able to get a usuable signal but it would drop off.

Thanks.

www.thegamefan.com

Proud owner of 3 HD DVD players and 170+ HD DVD movies.
rbarbier is offline  
Reply HDTV Technical

User Tag List

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page


Forum Jump: 

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off