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SX-28A Receiver Dynamic Range Test Results




 
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Author Topic: SX-28A Receiver Dynamic Range Test Results  (Read 27516 times)
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W1VD
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« on: September 30, 2008, 09:30:51 AM »

Receiver: SX-28A

Band    MDSBlocking DR   Two-tone DR
  (20 kHz)  (20 kHz)
80 meters   -140 dBm        102 dB    60 dB
40 meters   -139 dBm        103 dB    57 dB
20 meters   -139 dBm        108 dB    58 dB

For comparison, measurements on other boat anchor receivers can be found at

http://www.w1vd.com/BAreceivertest.html


Not bad for a 60+ year old receiver. On AM, listening to a properly aligned SX-28A is almost a mesmerizing experience!  With proper adjustment it's no slouch on cw either...     
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K3ZS
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« Reply #1 on: September 30, 2008, 10:00:11 AM »

Another thing I would like to know about old receivers, which ones use geared or friction tuning and which ones use dial-cord tuning.   Usually old receivers using dial-cord tuning need fixing.   One old receiver I found was impossible (for me) to restring it and having it work correctly.
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Tom WA3KLR
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« Reply #2 on: September 30, 2008, 07:34:27 PM »

It's interesting to note that the blocking DR is the best on 20 meters.

Thanks for your efforts Jay, I appreciate it.
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W8EJO
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« Reply #3 on: September 30, 2008, 08:04:21 PM »

The R390A & The HRO60 are 1-2 so far.
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WU2D
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CW is just a narrower version of AM


« Reply #4 on: September 30, 2008, 09:53:22 PM »

Just to round out the list we need to add the Heath HR-10 and the BC-348  Smiley
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KF8XO
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« Reply #5 on: October 03, 2008, 04:35:33 PM »

Just to round out the list we need to add the Heath HR-10 and the BC-348  Smiley

I'd want to see the Drake 2-B before an HR-10.
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K1ZJH
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« Reply #6 on: October 03, 2008, 05:05:10 PM »

probably don't have much effect, but does the IF stage skirt stop-band attenuation have any effect on those RXs with LC selectivity?

Pete
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K1ZJH
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« Reply #7 on: October 03, 2008, 05:06:59 PM »

HR-10 would be a hoot! Grin
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W1VD
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« Reply #8 on: October 03, 2008, 06:51:26 PM »

The receivers I've tested so far have a crystal cw bandwidth position which, when adjusted properly, have a reasonably good shape factor. I have a Drake 2A in the lab currently that will be tested over the weekend...followed by a 2B and 2C. The 2A has a minimum BW of 2.4 kHz (no xtal filter) so it will be interesting to see how it does.

While measuring the blocking and two tone dynamic range I normally switch to wider bandwidths looking for anything unusual. So far there has been no dramatic reduction in DR at the wider bandwidths so we're probably seeing the limitations of the rf amplifiers and/or mixers.

I'm limited to the receivers I have on hand (and adding to the collection) and those from several local collections. Always looking for more to measure but want to make sure all receivers are unmolested and working as close to factory performance levels as possible.

 

 

   
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KM1H
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« Reply #9 on: October 03, 2008, 08:20:39 PM »

Why not include 10 & 15M?  It would be interesting to compare designs as they progress from the 30's to 60's.

Add: pre war HRO, NC-240D, NC-183D, HQ-129X, HQ-140X, SP-200/SP-400 (or military version), SX-42, SX-115, 75A2, 51J4.

Carl
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K1ZJH
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« Reply #10 on: October 05, 2008, 12:08:20 PM »

Jay

For a receiver that didn't have a crystal filter to set CW selectivity, but did have an
internal Q-Multiplier, would you use the Q-Multiplier to set the CW bandwidth or just
go with the set's normal IF BW for the tests?

Pete
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W1VD
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« Reply #11 on: October 06, 2008, 08:15:09 PM »

Pete

Good question...one that I haven't had to address yet.

Guess I would measure it both with and without the Q multiplier. No doubt it would better the MDS but not sure what it would do to blocking and two-tone dynamic range - it would be interesting to see what happens. It's easy to add a footnote with additional measurement details.

What receiver did you have in mind?   
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w3jn
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« Reply #12 on: October 07, 2008, 08:45:15 AM »

Since the Q mult is so far down the IF chain I doubt it would have much effect on blocking and dynamic range.  These pefromance indicators are largely determined much farther up the signal chain - IE front end and mixer.
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WA1GFZ
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« Reply #13 on: October 07, 2008, 09:32:01 AM »

It will be interesting to see the effect of two strong signals on a Q mult. about to take off into oscillation.
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K1ZJH
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« Reply #14 on: October 07, 2008, 04:19:18 PM »

Since the Q mult is so far down the IF chain I doubt it would have much effect on blocking and dynamic range.  These pefromance indicators are largely determined much farther up the signal chain - IE front end and mixer.

For selectivity, to improve the MDS. That was the limiting factor for the Drake 2A, no narrow IF BW. Did the 2A have the optional Q-Mult speaker box??

Pete

Jay--one of the  Drakes with the Q-Multiplier speaker option. I'm sure it would improve the MDS, but I am
curious by how much..
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w3jn
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« Reply #15 on: October 07, 2008, 05:36:18 PM »

Pete, again, the Q mult is too far down the signal chain to do *much* improvement in the MDS.  That's largely determined in the front end and mixer...  I do concede it may have some effect but it may very well have the opposite effect because the Q mult, at its most selective, is on the verge of oscillation, hence lots of unstable/noisy stuff going on there.
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K1ZJH
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« Reply #16 on: October 07, 2008, 07:47:26 PM »

I must be missing something, but shouldn't decreasing the IF BW also directly affect the MDS? 

Pete

http://rfwireless.rell.com/pdfs/TN_WJhigh.pdf
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W1VD
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« Reply #17 on: October 07, 2008, 08:24:41 PM »

Yes...reducing the bandwidth should improve MDS. It doesn't seem that a stage on the hairy edge of oscillation can be a good thing for blocking and two tone DR. I suspect the Q multiplier stage will be 'captured' by both the large blocking and two tone signals. Tests will confirm this speculation. Have not had a receiver with Q multiplier in for testing...yet.
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w3jn
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« Reply #18 on: October 07, 2008, 08:59:59 PM »

I must be missing something, but shouldn't decreasing the IF BW also directly affect the MDS? 

Pete

http://rfwireless.rell.com/pdfs/TN_WJhigh.pdf

Indeed that is the theory, Pete, but a Q mult isn't really a filter; the regeneration can do some funky things.  I'm not saying that it absolutely will *not* reduce the MDS, just that I'm somewhat suspicious that it absolutely *will*.
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K1ZJH
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« Reply #19 on: October 08, 2008, 06:08:42 AM »

I must be missing something, but shouldn't decreasing the IF BW also directly affect the MDS? 

Pete

http://rfwireless.rell.com/pdfs/TN_WJhigh.pdf

Indeed that is the theory, Pete, but a Q mult isn't really a filter; the regeneration can do some funky things.  I'm not saying that it absolutely will *not* reduce the MDS, just that I'm somewhat suspicious that it absolutely *will*.


 I'm also curious to see what the Q Multiplier will do in practice; especially since it will be the principle CW selectivity provider for my HBR when it finished. That's why I raised the issue with Jay. The Drake 2A rx seems to have a poor MDS due to the 2.4kc stock BW. Some actual lab test results would tell a lot. Of course there are good Q mult circuits and poor ones, and the guy behind the controls would be a determining factor as well.

Pete
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WU2D
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CW is just a narrower version of AM


« Reply #20 on: October 09, 2008, 01:20:47 AM »

The better the receiver, the less help a Q-multiplier would make BUT in terms of raw MDS:

In practice the Q-multiplier will do what any filter would do but without the loss. It should be far more effective in terms of MDS than a lossy filter. It should beat a 4 kc mechanical filter for AM reception in this regard. Of course you do have to set it correctly!

I Have built them for several receivers and it helped them all, no matter the IF. The 455 Heathkits work good and they are easy to reproduce with a 12AT7 and a few parts. I have also built one each for the BC-348 and the 3-6 MHz command set for the 1450 kc IF and it works wonders on AM selectivity. Of course it can be made so sharp that it cuts sidebands severely.

Mike WU2D   (on the road)
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K1ZJH
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« Reply #21 on: October 09, 2008, 06:25:14 AM »

The better the receiver, the less help a Q-multiplier would make BUT in terms of raw MDS:

In practice the Q-multiplier will do what any filter would do but without the loss. It should be far more effective in terms of MDS than a lossy filter. It should beat a 4 kc mechanical filter for AM reception in this regard. Of course you do have to set it correctly!

I Have built them for several receivers and it helped them all, no matter the IF. The 455 Heathkits work good and they are easy to reproduce with a 12AT7 and a few parts. I have also built one each for the BC-348 and the 3-6 MHz command set for the 1450 kc IF and it works wonders on AM selectivity. Of course it can be made so sharp that it cuts sidebands severely.

Mike WU2D   (on the road)

I'm glad you posted those comments. I was lambasted on another "forum" for daring to suggest that a Q multiplier might offer some SSB selectivity improvement on IFs in the 1.415 to 2 MHz range by folks who were expressing opinions and not actual hand's on experiences.

Pete
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W1VD
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« Reply #22 on: October 09, 2008, 07:45:37 AM »

I-f filter loss, unless grossly high, won't have an affect on MDS in receivers that have a reasonable amount of gain ahead of the filters - an rf amplifier and mixer for example.  15 - 20 dB of 'front end' gain will make 10 dB loss that follows invisible as far as noise figure or MDS is concerned. 

An unusual receiver like the Squires SS-1R, with only a single relatively low gain active stage (on 40 meters), would be more likely to suffer MDS degradation with high filter loss.   
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WU2D
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CW is just a narrower version of AM


« Reply #23 on: October 11, 2008, 02:27:51 AM »

For receivers with a lack of gain in general, the Q-Multiplier helps greatly and a lossy filter would hurt.

I am talking about receivers that lack an RF stage or have low IF gain. You should see what one did to my buddies Sky Buddy! But don't expect miracles on a properly designed high performance receiver with excess gain, however.

Of course the added selectivity that it brings to the first IF does count. Every time the bandwidth is reduced in half, theoretically the sensitivity should improve 6 dB. I am not saying that you would get all of this but because of the cascade, it is going to do a lot being right up front. I think that this kind of idea does fit in with the classic HBR mentality of getting high performance from junkbox parts...

The idea can be extended further towards the front of the radio too. Have you heard of regenerative preselectors? These would not be a good idea in terms of IMD measurements, but if adjusted properly, you would vastly improve MDS.

Mike WU2D (on travel)
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wa2dtw
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« Reply #24 on: October 25, 2008, 10:24:46 AM »

Lately, there have been AM QSO's on about 1880, very close to 1885 which I frequent.  The SX-28 when tuned to 1885 is overpowered by strapping signals at 1880, even at narrow selectivity settings where the audio quality begins to deteriorate.   Is this to be expected with the SX-28, or do I need to play around with the alignment?
Thanks and 73
Steve WA2DTW
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