Well guys, I have read all the posts so far in this thread... The heliax notches do workquite well, but they are most certainly not "plug-n-play".
1) You must pay strict attention to the design criteria, maximum performance is obtained with repeated efforts. Resulting in a refined adaptation of your construction techniques. Forget the silly box on the top. <http://65.173.252.47/Six_Meter_Heliax_and_Helical_Duplexer_info/6m_duplexer _page.htm> Hollow-out the center and use the outer conductor as your housing. At least it is consistent in dimensions. 2) Tuning is waay critical... a MFJ antenna analyzer just doesn't get it done. Ask the demi-gods who worked their magic on Mount Waco. There is also a little bit of black magic in the works here... you keep at it until you stumble into the "right" mix. Then you do your darndest to replicate that accident! Make friends with you local comm-shop so they will lend you a network analyzer. Tune the filters in place... more on that in the next bullet point... 3) The heliax notches are inherently unstable in a mechanical sense. Any small shock can eliminate your tweaking efforts. I have dropped them on end just an inch or two, and the notch moved a hundred hertz or so. Now you are on the shoulder of the notch, and make no mistake.. it is a VERY sharp notch. It is something like balancing an ocean liner on the head of a pin.. that is if you truly want peak performance. I have noticed no issues with environmental (varying temps) effects as of yet. Cover the end with a metallic cover... leakage is a killer. I have constructed several sets. Most are in the county landfill! Thinking I would need 4 filters in each leg... I am now down to 3 in each leg and very impressed with the performance. I have not solved the mechanical instability issue as of yet.. still looking for the perfect glass-piston type cap to replace the "gimmick cap", and the perfect range for my pair (51.4/51.9). It seems to be a moving target.. or my techniques are just not as disciplined as needed for mass duplication.. yet. And you can forget shipping them. I agree with Skipp... partially.. I think the cost difference is more like 13dB better. The line was free, as was everything except for the roll-off components... maybe 10 bucks there... 40 bucks for good double-shield harness cable and connectors. Bottom line.. 50 bucks for a useable duplexer for 6m is a huge bargain! And you learn a lot along the way. 2yrs at it, and still learning how sloppy my work is. Skipp and I have been trading mail on this subject for about a year now... look closely at the design on a schematic level and I think you will see he is correct. Functionally there is little, if any, difference. Implementation of the design is the bear!! Good luck in your efforts.. and please share your findings. I am always looking for a better technique!! 73 Mike K5JMP www.k5jmp.us -----Original Message----- From: [email protected] [mailto:[EMAIL PROTECTED] Behalf Of skipp025 Sent: Wednesday, March 15, 2006 7:25 PM To: [email protected] Subject: [Repeater-Builder] Re: 6mtr duplexer > "steve" <[EMAIL PROTECTED]> wrote: > can anyone recommend a cheapish 6mtr duplexer, not a > home-made heliax one. If you take the electrical diagram of my commercial Decibel LB Duplexer and compare it to the heliax unit, you'll see they are the same animal. The Decibel Duplexer replaces the heliax with loaded cavities. Relative to the real world they are the same, work the same with the heliax units being -10dB or better in price. > Big problem is Iam in the UK and prices are very > expensive, around 900 UK pounds. > Thanks > Steve 1-5/8" hard line is cheap to find surplus and from ex broadcast sites. The construction information even works with 1-1/4 hard line. cheers, skipp Yahoo! Groups Links Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
