[hpsdr] Ideas for Munin Picked up at Dayton Hamvention

[Kjell Karlsen]

Hi Bob.

Sorry for not replying before, I have been very busy after coming home  
 from Crete.

I have done some more tests using different types of shielded wire on the  
T1.25X ferrite core and also an old T1.25-61. It seems as the permeability  
of the old one is higher so the return loss at 1.8 MHz is much lower.  
However, the linear power output is good and so is the efficiency even if  
the return loss is only 11 dB on 1.8 MHz.

The AVG22 shielded wire I have good access to is good even if I can see a  
very small increase in return loss using AVG20, that I have very limited  
access to. Using T1.25X, the return loss are:

1.8 MHz: 11 dB
30 MHz: 16.5 dB
50 MHz: 21 dB.

This is with only 330 pF for the compensating capacitor. That means that  
only 270 pF is needed in addition to the two 100 pF from each Drain.

The old T1.25-61 has the following return losses:

1.8 MHz: 19 dB
30 MHz:16.5 dB
50 MHz: 19.3 dB.

The best compensating capacitor is 300 pF for this one (250 pF + the two  
100 pF)

There must be possible to find AVG20 shielded wire for this transformer or  
25 Ohm coax that is not too thick.

With T1.25X and 330 pF compensating capacitance, the small signal gain  
varies +-4 dB from 1.5 to 55 MHz. When testing with 100W PEP, the GPB  
settings varies from 57 dB on 1.8 MHz to 52 db on 30 and 50 MHz so there  
is a lot of excess gain without the preamplifier installed.

The gain variation is of no importance when using HPSDR units as exciters,  
the Gain Per Band takes care of this. It might be possible to level this  
gain variation so you are free to experiment with this.

73, Kjell







På Wed, 23 May 2012 17:17:41 +0200, skrev Bob Mahrenholz <bobm at edge.net>:

> Sent this out a few days ago and didn't get any comments. Thought maybe  
> it did not go.
> Bob
>
>
> Hello Everyone,
>
> I really enjoyed Dayton this year. After looking at all of the booths in  
> the Exhibit Hall,
> I scoured the outdoor flea market looking for a small diameter co-axial  
> cable to use in
> winding T1 for the output stage of Munin.
>
> I found my answer at several of the places selling microwave components.  
> It is RG-178,
> (Belden 83265). It has an outside diameter of only 0.71 inches (1.803  
> mm). The center
> conductor is 30 AWG, insulation is Teflon, and the shield is silver  
> plated copper braid.
> Outer jacket is FEP. It's impedance is 50 ohms rather 25 but I do not  
> think that this would
> be a problem with the short length involved. Mouser's price is $364.62  
> for a 100' spool.
> (See below)
>
> It is a true co-axial cable rather than the "Control and Instrumentation  
> Cable" that Belden
> 83705 is. (Incidentally the 83705 is listed as "obsolete" in the Belden  
> Catalog.)
>
> The RG-178 may be found in Belden's Catalog:
>
>          https://edeskv2.belden.com/Products/#s=rg-178&r=0
>
> Click on the cable number and then click on "Detail".
>
> I purchased some 50' of the RG-178 at the Hamfest ($10  for a 25 foot  
> roll). if someone
> would like to try out a piece. I don't know what length it would take  
> for a single board
> but maybe some one of you knows.
>
> At the TAPR presentation at Dayton by Steven Bible, N7HPR, the TAPR  
> president,
> I learned that one of the functions of TAPR is to assist in the  
> development of new
> boards. I propose that we get TAPR to purchase a 100 foot roll of Belden  
> 83265 and
> then sell it in appropriate lengths to those of us putting together a  
> Munin board.
>
> 73,
> Bob, K4QQK
>
> p.s. Kjell, thanks for the info on the current measuring pins of J1.
>
>


-- 
Sendt med Operas revolusjonerende e-postprogram: http://www.opera.com/mail/

 1337807195.0