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AMfone's Online AM Handbook => Receivers => Topic started by: W1VD on September 30, 2008, 09:30:51 AM



Title: SX-28A Receiver Dynamic Range Test Results
Post by: W1VD 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 (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...     


Title: Re: SX-28A Receiver Dynamic Range Test Results
Post by: K3ZS 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.


Title: Re: SX-28A Receiver Dynamic Range Test Results
Post by: Tom WA3KLR 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.


Title: Re: SX-28A Receiver Dynamic Range Test Results
Post by: W8EJO on September 30, 2008, 08:04:21 PM
The R390A & The HRO60 are 1-2 so far.


Title: Re: SX-28A Receiver Dynamic Range Test Results
Post by: WU2D 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  :)


Title: Re: SX-28A Receiver Dynamic Range Test Results
Post by: KF8XO 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  :)

I'd want to see the Drake 2-B before an HR-10.


Title: Re: SX-28A Receiver Dynamic Range Test Results
Post by: K1ZJH 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


Title: Re: SX-28A Receiver Dynamic Range Test Results
Post by: K1ZJH on October 03, 2008, 05:06:59 PM
HR-10 would be a hoot! ;D


Title: Re: SX-28A Receiver Dynamic Range Test Results
Post by: W1VD 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.

 

 

   


Title: Re: SX-28A Receiver Dynamic Range Test Results
Post by: KM1H 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
KM1H


Title: Re: SX-28A Receiver Dynamic Range Test Results
Post by: K1ZJH 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


Title: Re: SX-28A Receiver Dynamic Range Test Results
Post by: W1VD 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?   


Title: Re: SX-28A Receiver Dynamic Range Test Results
Post by: w3jn 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.


Title: Re: SX-28A Receiver Dynamic Range Test Results
Post by: WA1GFZ 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.


Title: Re: SX-28A Receiver Dynamic Range Test Results
Post by: K1ZJH 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..


Title: Re: SX-28A Receiver Dynamic Range Test Results
Post by: w3jn 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.


Title: Re: SX-28A Receiver Dynamic Range Test Results
Post by: K1ZJH 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


Title: Re: SX-28A Receiver Dynamic Range Test Results
Post by: W1VD 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.


Title: Re: SX-28A Receiver Dynamic Range Test Results
Post by: w3jn 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*.


Title: Re: SX-28A Receiver Dynamic Range Test Results
Post by: K1ZJH 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


Title: Re: SX-28A Receiver Dynamic Range Test Results
Post by: WU2D 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)


Title: Re: SX-28A Receiver Dynamic Range Test Results
Post by: K1ZJH 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


Title: Re: SX-28A Receiver Dynamic Range Test Results
Post by: W1VD 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.   


Title: Re: SX-28A Receiver Dynamic Range Test Results
Post by: WU2D 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)


Title: SX-28 selectivity on 160M
Post by: wa2dtw 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


Title: Re: SX-28A Receiver Dynamic Range Test Results
Post by: Steve - WB3HUZ on October 25, 2008, 03:33:30 PM
Or in other words,


NFn = NF1 + (NF2 – 1)/Gain1 + (NF3 – 1)/(Gain1 – Gain2) + ….. +  (NFn – 1)/(Gain1 – Gain2 ….. Gainn-1)

where item 1 is the RF amp, 2 is the mixer, and so on.


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.   


Title: Re: SX-28A Receiver Dynamic Range Test Results
Post by: KM1H on October 26, 2008, 08:25:06 PM
This is where a 6 or 8 pole AM xtal filter would help. Mount under the chassis. There is more than enough IF gain in a SX-28 to overcome the insertion loss.

The single pole filter has poor skirt selectivity as shown in the manual. Turning off the AVC and backing down the RF gain may help a little.

Carl
KM1H



Title: Re: SX-28A Receiver Dynamic Range Test Results
Post by: Steve - WB3HUZ on October 27, 2008, 12:34:31 PM
Pre-WWII receiver are generally not give you the selectivity you require in this 5 kHz spacing scenario. More modern receivers will, but your audio quality will be reduced. With all the open space on 160, why in the world are AMers bunching so close together? Seems like operator problems rather than a receiver problem.


Title: Re: SX-28A Receiver Dynamic Range Test Results
Post by: wa2dtw on October 28, 2008, 09:50:15 AM
Steve
I try to keep the BC610 parked on 1885, because it is difficult to accurately change frequency using the tuning unit.  (a slight touch can move you about 10kc).
Lately, there are is significant AM activity on 1900 and 1878.   A strong signal there will wipe out anything at 1885 on the SX28.

73
Steve WA2DTW


Title: Re: SX-28A Receiver Dynamic Range Test Results
Post by: Steve - WB3HUZ on October 28, 2008, 11:17:26 AM
That's fine. What I've often found when I was in a QSO on 1885, someone else would start up a QSO on 1880. I find the sort of operating self defeating on AM. Spread out.


Title: Re: SX-28A Receiver Dynamic Range Test Results
Post by: WBear2GCR on October 29, 2008, 06:43:54 PM

There are some jim dandy ceramic filters that work great for 455kc IFs and also for 455KHz IFs as well... they're usually made by MuRata, although I think there are some from Toko Labs as well. Small and of good skirt for AM... some signal level padding going in may be required, and then some signal boosting going out depending on the levels in a given rig, but to go back up you can use a FET or bipolar (they'll handle the B+ if properly selected - come to think of it some MOSFETs will too) and the stage can be very simple (a triode config in solid state). Easy solution, and hides on a small board under the chassis, no blasting and reduction of the old rig's value...  ;D


                    _-_-bear


Title: Re: SX-28A Receiver Dynamic Range Test Results
Post by: Steve - WB3HUZ on October 29, 2008, 08:40:54 PM
No need for all that. Just get the Kiwa units.


There are some jim dandy ceramic filters that work great for 455kc IFs and also for 455KHz IFs as well... they're usually made by MuRata, although I think there are some from Toko Labs as well. Small and of good skirt for AM... some signal level padding going in may be required, and then some signal boosting going out depending on the levels in a given rig, but to go back up you can use a FET or bipolar (they'll handle the B+ if properly selected - come to think of it some MOSFETs will too) and the stage can be very simple (a triode config in solid state). Easy solution, and hides on a small board under the chassis, no blasting and reduction of the old rig's value...  ;D


                    _-_-bear


Title: Re: SX-28A Receiver Dynamic Range Test Results
Post by: N3DRB The Derb on October 31, 2008, 03:53:59 AM
Quote
NFn = NF1 + (NF2 – 1)/Gain1 + (NF3 – 1)/(Gain1 – Gain2) + ….. +  (NFn – 1)/(Gain1 – Gain2 ….. Gain-1)

hey man......how'd you get so funky? I don't believe that's ever been done on a record before.  :P


Title: Re: SX-28A Receiver Dynamic Range Test Results
Post by: Steve - WB3HUZ on October 31, 2008, 09:36:55 AM
It's gonna wipe out the moon walk!

Quote
NFn = NF1 + (NF2 – 1)/Gain1 + (NF3 – 1)/(Gain1 – Gain2) + ….. +  (NFn – 1)/(Gain1 – Gain2 ….. Gain-1)

hey man......how'd you get so funky? I don't believe that's ever been done on a record before.  :P
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