[hpsdr] VNA kit -- parts for reflection bridge for use with Hermes

[Dick Lichtel]

I like your ideas on the improvements and design and think the extra 
effort/time  is well worth the wait.

Dick KD4JP

On 11/12/2012 3:05 AM, David McQuate wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> QST:  all those interested in a reflection bridge for use with 
> Hermes.  There are currently 56 kits requested.
>
> The design being considered is one by Sam Wetterlin, who has built 
> several different reflection bridges, and has posted their printed 
> circuit designs on his web site. http://www.wetterlin.org/sam/      
> (look down about 2/3 of the page)
>
> Initially it seemed that only the MiniCircuits balun transformer was 
> needed, but many have expressed interest in having other parts added 
> to the "kit", especially the small diameter coax, the ferrite beads 
> and the printed circuit boards.
>
> The PCB layout for the "3 bead balun" reflection bridge requires 
> shortening the projections on a connector.  I would like to modify the 
> PCB design so no connector modification would be required, and so that 
> the board and connector really match well.  One respondent suggested a 
> connector made in China, and available in quantities of 100 on ebay at 
> very low cost---
>
> http://www.ebay.com/itm/100X-SMA-Female-Jack-Edge-Mount-PCB-PC-Board-Receptacle-Adapter-Connectors-New-/290691281049?pt=LH_DefaultDomain_0&hash=item43ae8cf099 
>
>
> I have received a dimensioned drawing of this connector from the 
> seller.  The PCB design could very easily be modified to accomodate 
> this connector.
>
> Are there any objections to using this connector?
>
> Digikey part numbers J716-ND   and   991-1047-ND   are also 
> possibilities.
> The first is much wider than the either the second or the ebay part, 
> so the PCB design would need greater changes.
>
> In addition, Sam has made suggestions for changes that I would like to 
> include that would increase the bridge's performance.
>
> Another suggestion is to combine the two small circuit boards of Sam's 
> design into one longer board, eliminating the connecting brass (shim 
> stock) strip.  This would increase the PCB area, and therefore the 
> cost, but it would also simplify construction.
>
> I would want to build at least one bridge using a modified PCB design 
> before building buying for more than 50, but this would require a few 
> weeks to accomplish.  Another reason to build one is to be sure of the 
> length of coax required to thread it 3 times through each of the 3 
> ferrite cores.  If I'm going to build one, I would need to purchase at 
> least 20 of the MiniCircuits balun transformers (their minimum 
> quantity).  On the other hand, if I know that more than 50 will be 
> wanted, it would make sense to just buy 100 at the outset, since 
> there's a substantial price break. (20 @ 2.19 each, 50 @ 1.49 each, or 
> 100 @ 1.19 each)
>
> It has also been pointed out to me that thewireman.com has RG-178 at 
> 0.55 per foot in 100 foot quantity, about half the price compared with 
> Digikey.  I think an 18-inch length would be more than enough--though 
> I would certainly want to try it before chopping up a lot of coax!  
> Similar consideration here regarding quantity.  100 feet would 
> probably be enough for 66 bridges.
>
> Now there may be some who would not want to wait that long, and who 
> would prefer to "roll their own", purchasing only the MiniCircuits 
> transformer from the group buy.
> Dick K9IVB is forging ahead independently & has posted parts lists for 
> all four of Wetterlin designs.  See near the bottom of: 
> http://k9ivb.net/hermes/
>
> Another issue is the possibility of sizing the PCB so it fits (nicely) 
> in some sort of (standard) enclosure (eg aluminum box).
>
> All these considerations seem to push out the time frame.  Is that 
> undesirable for some?
>
> I thank you for your consideration & comments!
> 73,
> Dave
> WA8YWQ
> _______________________________________________
> HPSDR Discussion List
> To post msg: hpsdr at openhpsdr.org
> Subscription help: 
> http://lists.openhpsdr.org/listinfo.cgi/hpsdr-openhpsdr.org
> HPSDR web page: http://openhpsdr.org
> Archives: http://lists.openhpsdr.org/pipermail/hpsdr-openhpsdr.org/


 1352725057.0