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| New Bridge Board |
Greg Ordy
Due to the interest in the January 2004 group build, a second build is planned. This build will be different in that the board will be commercially assembled. This will add approximately $60 to $100 to the price of the VNA kit, but will greatly reduce the work needed to complete a VNA. Assembly is still necessary, however. This is still a kit.
With the cost of assembly added in to the parts cost, the total cost will be approximately $260 to $300 (USD). The end of March, 2004, is the target completion date, but that is a very imprecise estimate at this point. The current delay on the oscillators is 6 to 8 weeks, and then there would need to be assembly after that. Perhaps it will end up being more like April.
If you are interested in getting on the list, or more information, please email me. An email link is on my home page.
Around May 10, 2004, the list for this group became full. Well, I guess it depends upon how you count. Let me explain.
Based upon earlier head counts, I ordered 45 oscillators. Those are the long lead-time items (8 to 10 weeks) that also are the most expensive single part in the VNA. As I went through the process of establishing a relationship with the board assembly folks, I learned that due to the way that they packaged their services, the minimum run of boards that made financial sense was 50 boards. So, I need to have 50 boards assembled, no matter how many have oscillators. At the same time, there are several members of the group who only want a kit of parts, not the assembled boards. That adds a few units of parts to the overall order.
I just hit 45 group members, although a few are interested in the kit of parts. They won't claim an assembled board, but they will claim an oscillator. At the very least, I need to order some more oscillators, but those won't be available for another 8 to 10 weeks.
So, if you contact me past this point in time, I can put your name on the list. If people drop off of the existing list, then anything can happen. But if the existing group holds firm, then the oscillators are already all spoken for, and more won't be available for 2 additional months (at least through me). There are still a few more assembled boards (without oscillators) that will come out of this batch.
What I'm really doing is simply making a list of names, ordered by time. When there is something to ship, such as a board or parts, I will start down the list, asking each person to ether take assembled boards, or a kit of parts. I'll stop asking when I reach the end of the list, and if anything is sold out, then that alternative is no longer available, until more parts (probably oscillators) are delivered.
The part controlling the timing of the batch is the master oscillator. The current delivery date is May 18th, 2004. The hope is to have the boards assembled prior to that time, so that the oscillator can be added, the board tested, then shipped.
This batch of boards will include a reworked T1-6T bridge board, thanks to Todd Nichols. The rework includes plated thru holes, which improves the bonding between the top and bottom sides of the board. The board dimensions were adjusted to fit snugly into a Hammond 1590A die-cast aluminum enclosure. This is one of the few commercial cases which is near the approximate size needed. The spacing between the RF DDS input connector and detector input connector has been reduced to 2.0 inches from 2.5 inches used on previous generations of boards. This brings the connectors in from the corners of the enclosure, which simplifies assembly. I had to use small flange N connectors with the previous board, to clear the corner posts of the box. With the reduced spacing, normal flange connectors should fit. Optional port P2 is now accessible off of the left side.
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| New Bridge Board |
This picture shows the new bridge board laid on top of the Hammond 1590A case, which was used with the old bridge board. As can be seen, the board completely spans the top to bottom dimension of the enclosure. The connectors will need to be repositioned for the new board, but they become more centered. Here is a picture of the old bridge board, which was not tall enough to span the case, and was so wide that it interfered with the corner posts.
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| Old Bridge Board |
Of course this whole enclosure issue is optional. Many VNAs have been built with SMA connectors soldered directly to the sides of the boards, and that can be done with the new bridge boards. But, in some cases, the intent is to take the bridge outside, and connect it to heavy transmission lines. In these cases, the bridge needs some protection and support, since the naked board would probably just crack in half, or crack at the connectors. For those situations, the Hammond 1590A enclosure can be used with the new bridge board.
I finally had the chance to build a new bridge board and install it into the 1590A enclosure. That project is described on another page.
Some final information, as the end nears for this group. Part of the goal has been to reduce the paper sent in the boxes, since paper, relatively speaking, is heavy, and hard to change once printed. There is one page for the assembled boards, and one page for the parts kits. I will keep these pages up to date with whatever information I have. The other pages cover technical topics related to this group.
Back to my Experimentation Page