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W2BBQ
03-30-2010, 05:33 PM
This is about Double vs Triple vs Quadruple Conversion of HF rig Receiver Schemes.

I had always been under the general impression that this had the most to do with adjacent frequency rejection.

A triple conversion receiver will be less effected by interference, harmonics, "bleedover" ect...from stronger signals on nearby/related frequencies than a double conversion receiver would....and so on through quad conv.

Back a while I had an Icom 751A, Quad Conversion and the thing was a tank. It was nearly "bleedover proof."

But I see modern high end rigs over $5,000 that are only double conversion. Have they made up the specs utilizing other components to do the job of adjacent frequency rejection?

Or what else is going on here?

Thanks for assistance! http://www.pic4ever.com/images/interview.gif

KL7AJ
03-30-2010, 05:37 PM
This is about Double vs Triple vs Quadruple Conversion of HF rig Receiver Schemes.

I had always been under the general impression that this had the most to do with adjacent frequency rejection.

A triple conversion receiver will be less effected by interference, harmonics, "bleedover" ect...from stronger signals on nearby/related frequencies than a double conversion receiver would....and so on through quad conv.

Back a while I had an Icom 751A, Quad Conversion and the thing was a tank. It was nearly "bleedover proof."

But I see modern high end rigs over $5,000 that are only double conversion. Have they made up the specs utilizing other components to do the job of adjacent frequency rejection?

Or what else is going on here?

Thanks for assistance! http://www.pic4ever.com/images/interview.gif

If you remember the Collins R-390, it had four conversions....sort of. One of the conversions was a tuneable I.F. stage.

The trend is actually AWAY from multiple conversions. Every time you have a converter, you have a chance of generating internal birdies...which may be worse than what you're trying to eliminate in the first place. In fact, the Direct Conversion receiver is pretty standard in all your high end scientific applications where you MUST know what you're looking at.

Eric

N0SYA
03-30-2010, 05:51 PM
Hi
Yeah, the trend is away from multi conversion, unless it's direct conversion. When they come out with cheap adc chips that can do an honest 150dB dynamic range, look out! Multiconversion rigs also employed that scheme as a means to cheaply filter the IF, along with increasing resistance to images. A crystal filter at 8MHz is normaly cheaper to make than one at 455Khz, although of the same bandwidth and poles at 8MHz may typically have worse specs than the filter at 455KHz. Also with the increased birdie problem with multiconversion rigs, you have to terminate the mixers for all freq responses, usualy with a diplexer. If you don't, the rig may act crazy.

As to sdr dc rigs, you run into things like dithering and aliasing and all sorts of responses that come along with dsp, and this comes down to carefull design, programming, and quality parts. As always, the more you pay, the less spurii you put up with.

KC9KXW
03-31-2010, 08:55 PM
I'm just curious as to "WHAT KIND OF RIG" we are talking about here. If its just a receiver he needs to stay (OUT) of the cell phone bands and others that are not allowed per FCC rules on his receiver.

If its a Transceiver he needs to stay (OUT) of the out of band frequencies, ie CB, Public Services (POLICE, FIRE, AMBULANCE, ETC.) again per FCC rules.

Just be "VERY CAREFUL" of what your doing to that RIG, and please ELABORATE on the RIG in question. I'm not trying to start any fights or problems with the "CONVERSION QUESTION", but there has been a lot of trouble in the past about "CERTAIN" conversions here on the ZED.

Otherwise good luck on your venture. :)

73 Jim
DE KC9KXW

W0LPQ
03-31-2010, 09:06 PM
9KXW I do not understand your response ... nothing was alluded to regarding building a receiver ... just questions about the conversion schemes within the receiver.

The Kenwood 450/690 used 8.3 Mhz and 455 Khz for IF's. Used to have 690 and it was pretty fair at receiving with minimal birdies (internal generated).

By the way ... BBQ has been around for a day or three and knows what is and what is not legal. This is not germain to the question asked.

KD7MSC
03-31-2010, 09:09 PM
I'm just curious as to "WHAT KIND OF RIG" we are talking about here. If its just a receiver he needs to stay (OUT) of the cell phone bands and others that are not allowed per FCC rules on his receiver.

If its a Transceiver he needs to stay (OUT) of the out of band frequencies, ie CB, Public Services (POLICE, FIRE, AMBULANCE, ETC.) again per FCC rules.

Just be "VERY CAREFUL" of what your doing to that RIG, and please ELABORATE on the RIG in question. I'm not trying to start any fights or problems with the "CONVERSION QUESTION", but there has been a lot of trouble in the past about "CERTAIN" conversions here on the ZED.

Otherwise good luck on your venture. :)

73 Jim
DE KC9KXW

LOL!!
..............

AC0FP
03-31-2010, 09:20 PM
I think the best trade off between receiver spurious responses and adjacent channel selectivity (overload) is dual conversion. Of course the IF filter selectivity and balance between each filters skirt has a lot to do with how good the receiver performs. A 455kHz ceramic filter seems to give the best performance with the lowest cost, mainly because they are cheap to produce compared to other filters.

I built a single conversion transceiver for 6 meters and I used a 9 MHz 8-pole crystal filter made by KVG and the receiver had excellent performance! You can buy that same filter today from KVG for around $350. Volume costing to the manufacturer for a SSB ceramic 455kHz filter today is probability < $2.00.

73,

fp :)

W8ZNX
03-31-2010, 09:21 PM
Jim

subject at hand
has to do with how receivers work

not about what is or is not legal

K5UOS
03-31-2010, 09:26 PM
This is about Double vs Triple vs Quadruple Conversion of HF rig Receiver Schemes.

I had always been under the general impression that this had the most to do with adjacent frequency rejection.

A triple conversion receiver will be less effected by interference, harmonics, "bleedover" ect...from stronger signals on nearby/related frequencies than a double conversion receiver would....and so on through quad conv.

Back a while I had an Icom 751A, Quad Conversion and the thing was a tank. It was nearly "bleedover proof."

But I see modern high end rigs over $5,000 that are only double conversion. Have they made up the specs utilizing other components to do the job of adjacent frequency rejection?

Or what else is going on here?

Thanks for assistance! http://www.pic4ever.com/images/interview.gif


The popular Elecraft K2 is only single conversion. Technology has come a long way in the last several decades.

http://www.elecraft.com/Apps/why_is_the_k2_receiver_single.htm

K5UOS

KC9KXW
03-31-2010, 10:54 PM
Jim

subject at hand
has to do with how receivers work

not about what is or is not legal

ZNX,

THANK YOU FOR LETTING ME (TAKE OFF) MY FLAME SUIT.

AND AS FOR THE """FLAMERS""", HEY HE (W2BBQ) WAS ASKING ABOUT (CONVERTING). WELL I WAS SIMPLY GIVING HIM SOME ADVICE IF HE (WAS) CONVERTING HIS RIG AS THERE HAS BEEN A LOT OF QUESTIONS ABOUT CONVERTING RIGS.

MAYBE I DIDN'T QUITE UNDERSTAND THAT HE WAS JUST ASKING ABOUT HOW THE RADIO WOULD ACT AND THE THEORY OF IT. HEY GIVE ME A FRICKEN BREAK, I JUST HAD A STROKE (((6 WEEKS AGO)))!!!!!!!!!!!!

LPQ,

I UNDERSTAND HE ISN'T BUILDING A RECEIVER, HE DID SAY SOMETHING ABOUT CONVERTING AND THAT'S WHAT MY RESPONSE WAS ABOUT. I'M SURE THAT EVERY WHO READS (KD7MSC IF YOU CAN READ, AND YOUR "LOL" WAS AS POINTLESS AND LAME AS YOU ARE, "SO LEARN TO REREAD THE THIRD SENTENCE IN MY POST")!!!!!!!!!!!!

AS I STATED I WAS NOT TRYING TO START ANY FIGHTS OR PROBLEMS. I WAS MERELY TRYING TO HELP BY HAVING HIM BE CAREFUL ABOUT THE CONVERSION ITSELF.

I'M SORRY THAT I MISUNDERSTOOD THE QUESTION, AND TO THOSE WHO STRAIGHTENED IT OUT FOR ME I DO APPRECIATE IT, THANKS.

73 Jim
DE KC9KXW

KD7MSC
03-31-2010, 10:58 PM
(KD7MSC IF YOU CAN READ, AND YOUR "LOL" WAS AS POINTLESS AND LAME AS YOU ARE, "SO LEARN TO REREAD THE THIRD SENTENCE IN MY POST")!!!!!!!!!!!!


So is that some kind of personal attack? LOL! You are way to serious. You probably should have read the first post and understood what the subject was about before you put on your self appointed moderators hat. Good luck OM.
73, Sean

W0LPQ
03-31-2010, 11:59 PM
9KXW, as I said ... conversion ... not converting. He is speaking of the conversion to the I.F. INSIDE the radio ... not converting somerthing.

Read...!

KA4DPO
04-01-2010, 12:04 AM
If you look at the block diagram of the Flex radios they use a Direct Conversion front end which is single conversion. Rejection of unwanted signals is done by the DSP software and is superb.

The old Drake TR3 and TR4 transceivers were all single conversion and worked beautifully. Multiple conversion was a way to maximize IF rejection and unwanted signals but as Eric pointed out it sometimes backfired.

Most of the modern triple conversion DSP radios have two levels of RF (analog)conversion ahead of the third IF which is the DSP. The third converter usually operates in the 20 to 40 KHZ range so it is really not quite a radio frequency but is above the audible range.

W3JN
04-01-2010, 01:26 PM
Wow. Who knew such an innocuous question could generate so much hate :D

The only reason in the past for multiple conversion schemes is to maximize image response while offering a choice of narrow band IF filters. However the more mixers and LOs you have going, the more chance you have for spurious responses. The old Collins SSB manual, as I recall, had some n-order spurious response charts, and when you get more than a couple of LOs running it's a huge challenge to make sure nothing accidentally beats with something else causing a spurious response.

With DSP and advances in mixer design, we aren't as concerned with images as we are rejection of strong signals a small percentage away in frequency. Despite recent advances in A/D technology, I'm a firm believer in a good roofing filter - *then* down conversion to a low IF for the DSP to attack. This helps ensure the crap stays out of the A/D converter.

BTW direct conversion isn't single conversion, it's direct conversion. Single conversion implies one IF frequency; direct conversion has no IF.

W0LPQ
04-01-2010, 01:48 PM
3JN, you are correct ... if 9KXW had not started his diatribe, probably 10 of the 14 posts would not be here.

The old yellow SSB Principles Collins book was almost a bible. It did indeed have many pages of spurious response data. I gave mine away years ago to a EE student at Iowa State. Should have kept it ... but he had a need for some data ... to this day he still has it.

Many radios upconvert to a VHF frequency, while some go the other way.

You are also correct about single conversion versus direct conversion. The old All-American-Five was a single conversion ... 455Khz radio. As I remember, the Collins 651S-1 was a triple conversion radio .. and it did upconvert, but have long forgotten the exact scheme. As has been said before in several threads, old USN WWII radios were direct conversion so as to eliminate the local oscillator radiation and having an enemy vessel locate them. That was a trick in itself to make a good receiver, but the RBA/RBB/RBC series was darn good ... stable also. Some of them were regens and thanks to great shielding, had very little radiation.

AI3V
04-01-2010, 01:59 PM
Another reason to use multiple conversions is to keep the gain at any one frequency low, in order to compensate for inadequate shielding between stages.

A direct conversion receiver might have 100+ db of audio gain, it is more difficult to isolate the input and output than if you use, say, a triple conversion with 33db gain at each frequency.

The more "conversions" the greater the chance of birdies, or spurious response.

Using a "high side" conversion scheme may improve image rejection.

Rege

KA4DPO
04-01-2010, 02:01 PM
Wow. Who knew such an innocuous question could generate so much hate :D

The only reason in the past for multiple conversion schemes is to maximize image response while offering a choice of narrow band IF filters. However the more mixers and LOs you have going, the more chance you have for spurious responses. The old Collins SSB manual, as I recall, had some n-order spurious response charts, and when you get more than a couple of LOs running it's a huge challenge to make sure nothing accidentally beats with something else causing a spurious response.

With DSP and advances in mixer design, we aren't as concerned with images as we are rejection of strong signals a small percentage away in frequency. Despite recent advances in A/D technology, I'm a firm believer in a good roofing filter - *then* down conversion to a low IF for the DSP to attack. This helps ensure the crap stays out of the A/D converter.

BTW direct conversion isn't single conversion, it's direct conversion. Single conversion implies one IF frequency; direct conversion has no IF.



Technically thats true. I guess the IF is at audio where the DSP takes care of the image response and filtering.

AI3V
04-01-2010, 02:03 PM
As has been said before in several threads, old USN WWII radios were direct conversion so as to eliminate the local oscillator radiation and having an enemy vessel locate them.

Nope.

DC receiver LO will radiate just fine, thank you.

Military receiver, like the r-1051 is all solid state, except for a pair of tubes in the receiver front end.

The 2 tubes are used to keep the LO from sneaking out the antenna jack and being radiated.

Rege, TEMPEST rated, USS Midway CV41

N0SYA
04-01-2010, 02:08 PM
and here i thought those tubes where to keep sunshine canned in russia from popping the rig!

AI3V
04-01-2010, 02:15 PM
That was a close second, But from the couple times the Russians surprised us with a Bear flyover convinced me that any atomic attack on the ship would be successful.

MAD and all that insanity.

Rege, Who hopes the Russians love their children too.

W0LPQ
04-01-2010, 02:31 PM
3V ..."DC receiver LO will radiate just fine, thank you."

Direct conversion and Local Oscillator do not equate. Don't have one.

R-1051 was not around in WWII. RBA/RBB/RBC were.

I guess you have never seen the internals on those radios. Plenty of shielding to begin with.

KA9MOT
04-01-2010, 02:42 PM
In a Dual Conversion, only so much can be accomplished.....Quad Conversion is much better. The receiver can be converted 4 times into 4 completely different devices.

An Example:

Conversion 1: Convert to a transceiver.

Conversion 2: Convert to a Personal Computer

Conversion 3: Convert to a HDTV

Conversion 4: Convert to an Electric Car so we can all ride around on April Fools Day!

Happy April Fools Day!

KA9MOT
04-01-2010, 02:46 PM
I'm just curious as to "WHAT KIND OF RIG" we are talking about here. If its just a receiver he needs to stay (OUT) of the cell phone bands and others that are not allowed per FCC rules on his receiver.

If its a Transceiver he needs to stay (OUT) of the out of band frequencies, ie CB, Public Services (POLICE, FIRE, AMBULANCE, ETC.) again per FCC rules.

Just be "VERY CAREFUL" of what your doing to that RIG, and please ELABORATE on the RIG in question. I'm not trying to start any fights or problems with the "CONVERSION QUESTION", but there has been a lot of trouble in the past about "CERTAIN" conversions here on the ZED.

Otherwise good luck on your venture. :)

73 Jim
DE KC9KXW

Just to help ya' out Bro:

http://www.hitecrcd.com/support/product-support/faqs/receivers/general-receiver/what-is-the-difference-between-dual-conversion-and-single-conversion.html

W8JI
04-01-2010, 03:07 PM
3V ..."DC receiver LO will radiate just fine, thank you."

Direct conversion and Local Oscillator do not equate. Don't have one.



That isn't true. Direct conversion receivers always have a local oscillator.

W3JN mostly wins the prize on this thread, but I'll add a few things to what he said:


The only reason in the past for multiple conversion schemes is to maximize image response while offering a choice of narrow band IF filters.

There were other reasons. Constant tuning rate and stability is one additional reason for using multiple conversion schemes. By using a tunable lower IF section, the front end can be crystal controlled block converters. My homebrew receiver from 1964 is that way. It has a 1.8 - 2 MHz dual conversion receiver with 1650 and 50 kHz IF systems, and adds converters ahead of that for 80-10.

This means the tuning rate and calibration is identical on every band, and even ten meters is crystal controlled so it has about the stability of the system on 160.



However the more mixers and LOs you have going, the more chance you have for spurious responses. The old Collins SSB manual, as I recall, had some n-order spurious response charts, and when you get more than a couple of LOs running it's a huge challenge to make sure nothing accidentally beats with something else causing a spurious response.

With DSP and advances in mixer design, we aren't as concerned with images as we are rejection of strong signals a small percentage away in frequency. Despite recent advances in A/D technology, I'm a firm believer in a good roofing filter - *then* down conversion to a low IF for the DSP to attack. This helps ensure the crap stays out of the A/D converter.

BTW direct conversion isn't single conversion, it's direct conversion. Single conversion implies one IF frequency; direct conversion has no IF.

73 Tom

W3JN
04-01-2010, 04:06 PM
Indeed, most Collins receivers used this to good advantage. Most transceivers until the advent of synthesized LOs also use this - but killing images was still one of the goals until the advent of up conversion to a VHF first IF.


Technically thats true. I guess the IF is at audio where the DSP takes care of the image response and filtering.

No. If you convert to baseband, it's not an intermediate frequency. The DSP doesn't take care of the image response, since with a direct conversion receiver the image is just a mirror image of the baseband (a "negative frequency", if you will) and can be ignored.

Not all direct conversion receivers are intended to be front ends for DSP. Direct conversion receivers have been around for years before DSP. Most DSP inputs want an I and Q, which is accomplished with 2 mixers fed with a LO signal in-phase, and one 90 degrees out of phase. WIth receivers having a very low IF, intended for DSP use, I/Q and phase shifting is a necessity, and is called a image reject mixer.

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