[ARC5] A simple receiver improvement

[Glen Zook]

Carl:

The sensitivity improvements are definitely NOT imaginary!  The improvements have been measured, numerous times, using well calibrated signal generators such as Motorola (Systron Donner), Singer-Gertsch, IFR, etc. service monitors as well as with older, but still well calibrated signal generators, like the HP-606, HP-608, URM-25 series, TS-497 series, Measurements Models 65 and 80, and so forth.

That is, running 50-ohm, unbalanced, matched impedance signals into the balanced terminals (with A-2 grounded) per "normal" practice and then with the television balun inserted with the A-2 terminal not connected to ground.

I agree that building baluns that are specifically matched to the actual impedance of a particular receiver and to 50-ohm coaxial cable should produce even better sensitivity.  However, for less than $1.00 for the television balun, the improvement in usable sensitivity is generally remarkable and building more accurate baluns is not usually worth the effort and cost versus the additional apparent gain.
 
Glen, K9STH


Website:  http://k9sth.com



On Tuesday, January 14, 2014 5:31 PM, Glen Zook <gzook at yahoo.com> wrote:
 
The Hammarlund receivers, up to, and including, the HQ-150 (also includes the HQ-100 and HQ-110 which are later receivers) have balanced antenna inputs up to 600-ohms and the baluns should definitely help.  The HQ-160 has an antenna impedance of around 75-ohms unbalanced and the HQ-170 series and HQ-180 series have an antenna impedance of 100-ohms balanced / unbalanced (depends on if the A-2 terminal is connected to ground).  With those receivers, using a television balun probably wouldn't do much good.
 
Glen, K9STH


Website:  http://k9sth.com



On Tuesday, January 14, 2014 3:35 PM, Kenneth G. Gordon <kgordon2006 at frontier.com> wrote:

On 14 Jan 2014 at 12:56, Ian Wilson wrote:

> Ken,
> 
> In principle you could just use an L-network or something to couple
> more energy from the antenna to the tuned circuit of the first RF
> stage. However .. this will reduce the selectivity of that tuned
> circuit, so you may run into diminishing returns.
> 
> 73, ian K3IMW

That is an idea.

However, I looked up some balun design math.

Z2 = n^2*Z1

where n = the turns ratio, Z2 = one impedance and Z1 = the other.

n in this case turns out to be about 4.4

This means that one would wind 5 turns on the "primary" side, and 22 turns 
on the secondary side to achieve a 50:4.1K balun.

Now I have to figure out which mix of toroid I would have to use.

This seems do-able and small enough.


Ken W7EKB
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