[Premium-Rx] Premium RX Strong Signal Performance

[Barry Hauser]

Hi John & List:

I am by no means an expert in these, but, for what it's worth:

When I initially get a receiver in here, I usually tinker around with a makeshift antenna -- a few feet of wire strewn about.  That's enough to check for reception on most bands and all I'm doing is checking for signs of life.  

When I got the RF-550 and did the usual, it was practically deaf with a few feet of wire.  Not until I added more and clipped it to various random objects ( a true random antenna ;-) did it perk up. Actually, of all the odd items I tried, it preferred me best.

Subsequently, the manual arrived and it makes mention of and illustrates an additional Hi-Z antenna option, RF-567 which adds J10 and J11 at the upper left of the rear panel.  To use it, you connect the antenna to J10 instead of J1 and use a BNC patch cord between J1 and J11.  Apparently, this is just a balun and two BNC jacks -- an after-the-fact tweak.  They say it's for short, untuned antennas.

However, the sense I got during a bit of tinkering was that the regular 50 ohm antenna input (J1) is touchy.  Ohms may be ohms, but there there are things like Q, I suppose.  I know the W-J's and RA6790GM's were not like this at all, and nominally the antenna inputs are 50 ohms on those also -- but that's "nominal".

I'm not familiar with that Lankford whip. Is there some way to tune impedance or input match it?  Try the same thing as I did -- short piece of wire and hold the end.  Of course, you're body impedance and Q may vary from mine ;-)

I know the AC ground is reasonably good as these things go on the wall outlet.  The receiver was not separately grounded when I did this -- but I've done the same thing with any number of receivers of all degrees of premium-ness and vintage and never noticed one that was as fussy as this one.  A bit odd that they went to the trouble of coming up with a retro-fit "option" for the HiZ input and implemented it by means of a jumper arrangement.  Many receivers, as you all know, come with Hi and Lo Z inputs as standard.  Often, I don't notice much of a difference with a hank of wire.

Just possible the RF-550 (and the 590?!) didn't "like" the Lankford whip "as was".  Is it possible the 550 and 590 have the same antenna input design?  Or could aging of the components put the actual impedance way out?

Possibly somewhat related, I recently read some posts somewhere about adding a balun -- even the 300/75 ohm TV twinlead to cable type -- to improve matching.

Barry

  ----- Original Message ----- 
  From: John Reed 
  To: Premium RX 
  Sent: Thursday, May 29, 2003 1:30 PM
  Subject: [Premium-Rx] Premium RX Strong Signal Performance


  I recently moved to a new location and discovered that there is a meduimwave broadcast station on 1450 KHz about 1/2 mile from my location with 5000 watts of power.  This has given me the opportunity to test various receivers in the strong field of this station.  For an antenna I'm using Dallas Lankford's Ultralinear whip with push-pull second stage.  There is a weak station on 1460 KHz and the test is based on how well this station can be heard.

  Here are some results, in order of best to worst:

  Racal RA6793A - good readability.  I used USB and manual AGC.  RF gain was turned down to give the best signal.

  Racal RA6772E - essentially the same performance as the RA6793A.

  WJ DMS-105R - more splatter.  I used 20 dB of input attenuation and the gain controls for best signal.  This receiver is single conversion so there is no roofing filter, also analog tuned so phase noise is minimal.  Still not as good as the Racals.

  NRD-525 - more splatter and noise than the above receivers.  This is not a stock 525.  It has the ESKA roofing filter and PLAM board with post IF filters.

  Harris RF-550 - Very noisy and splatter was bad.  Just pieces of the received signal could be made out.  USB was used, manual gain and RF and audio gain were adjusted for best reception.

  Harris RF-590 - about the same as the 550, but not as much signal made it through.

  I am surprised at the wide range in performance between these receivers.  The published specs don't indicate to me that much of a difference should exist.  I'm curious as to what specs would be most important in quantifying this test?

  John Reed




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