INRAD filters - I am confused again!

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JJ2013
Voodoo Audiophile
Posts: 141
Joined: Sat Apr 27, 2013 9:16 pm

INRAD filters - I am confused again!

Post by JJ2013 » Sat Aug 02, 2014 10:05 am

Hi y'all Audioheads, Audiophiles and VooDoo Audio Gurus!

I hear about the 4 kHz filter (for the 2nd IF) from INRAD that I may want to put in my TS950SDX! I am hoping that replacement would be a pretty straightforward affair?

Could you tell me if it is the 4 kHz filter shown on the web site below?
http://www.inrad.net/product.php?produc ... =59&page=1

I am a tad confused about replacing the existing Kenwood filter YK-88A as according to the Inrad web site their filter #475 could be used, but it says the #475 is an 8 pole AM filter? Despite that I take it that installing #475 could widen out the TX bandwidth on SSB too, correct? Also, there is a serious insertion loss that I don't like at all given that my antenna set-up is pretty modest as it is!

Note, the TS950SDX I have is (for now!!) unmodded although the VooDoo Phasing Mod has been done and it does have the very latest firmware.

Sure would appreciate some clarity on this!

Cheers!

JJ

BillPaul
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Joined: Wed Jan 19, 2011 11:52 am

Post by BillPaul » Fri Aug 08, 2014 4:02 pm

There's a couple of problems with what you want to do here.

You state that your goal is to widen your AM response. That being the case, filter #475 is not going to help you at all. In fact it's going to make things worse.

An AM signal is composed of three pieces: the carrier, an upper sideband and a lower sideband. The upper and lower sidebands are basically mirror image copies of each other. This means you're transmitting the same audio information twice.

This means that for AM, you need a filter that is twice as wide as your desired audio bandwidth. If the YK-88A is 6KHz wide, that means you get a total of 3KHz of audio bandwidth. The Inrad model #475 is only 4KHz wide, which means you'd be limited to only 2KHz of audio bandwidth. This is why they labeled it as a narrow-band replacement for the YK-88A.

Furthermore, there's a few other factors that come into play here. Remember that the TS-950SDX uses the DSP unit for both SSB and AM modulation. By default, the DSP will limit you to 3.1KHz of TX bandwidth on AM. If you use the power-on mod to enable 6KHz of bandwidth, that will only work on SSB unless you have a specially patched firmware. (There's an article in the modifications section which describes it.)

You said you have the latest firmware. You did not say if you had the patched firmware with the HiFi AM mod. There used to be a guy in eBay selling ready made EPROM chips that you could use to upgrade, but I don't think he's doing it anymore. I don't know if you obtained a chip or burned one yourself. If the latter, you can download the modified EPROM image from here:

http://people.freebsd.org/~wpaul/ts-950 ... patch.html

Also, you can use the service menu to allow you to change both the 1st and 2nd IF filter settings for TX as well as RX. This includes setting the 2nd IF filter (8.83Mhz) to bypass, where the filtering is completely disabled. This in conjunction with the firmware mod above will give you the widest possible TX bandwidth (6KHz, basically the same as the radio's eSSB bandwidth).

If you download the firmware patch file at the bottom of the page mentioned above, it contains a FAQ.txt file which explains how to change the service menu setting and enable the "off" setting in the LPF menu (for full HiFi mode).

Lastly, note that the 1st IF (455KHz) filter setting doesn't have a bypass (all off) position like the 2nd IF setting does. This setting actually has no effect on AM transmit, but it does affect AM receive. You can set it to 12Khz, which is not bad, but you can also easily create a bypass setting, as long as you don't mind giving up one of the extra narrow CW filter slots. Basically, you can connect a jumper wire in the place where the optional CW filter would go and just pretend it's a bypass setting. This will give you a little better bandwidth on RX. If you don't have the optional extra narrow CW filter in your rig, the slot is just sitting there unused anyway. :)

-Bill, N1GPT

JJ2013
Voodoo Audiophile
Posts: 141
Joined: Sat Apr 27, 2013 9:16 pm

Post by JJ2013 » Fri Aug 08, 2014 6:34 pm

Hi Bill,

I have seen you respond to many questions posed by others and do recognize that you really know a lot!
My problem is that I tend to make things that are simple complicated and also not provide enough background information or write so poorly that I end up wasting everyone’s time……Interspersed within your response, following the # sign, see my counter-comments 
There's a couple of problems with what you want to do here.

You state that your goal is to widen your AM response. That being the case, filter #475 is not going to help you at all. In fact it's going to make things worse.

# My goal is have a reasonably wide SSB TX pass-band, "only" around 4 kHz+ ;-)) Also, I am feeding audio in through the front mic-jack with known limitations associated with this approach. When playing audio and striving to get everything dialed in, I have my TS870 on to monitor my audio. I am using a condenser mic that appears to fit my natural speaking voice well and Behringer outboard gear with a Jensen Audio Isolation transformer (their PI-XX box with the transformer in it) as the last piece of hardware just before the mic jack. I am feeding audio in a balanced manner into the front (I am using star quad cables) from the Audio OUT of the PI-XX.

An AM signal is composed of three pieces: the carrier, an upper sideband and a lower sideband. The upper and lower sidebands are basically mirror image copies of each other. This means you're transmitting the same audio information twice.

This means that for AM, you need a filter that is twice as wide as your desired audio bandwidth. If the YK-88A is 6KHz wide, that means you get a total of 3KHz of audio bandwidth. The Inrad model #475 is only 4KHz wide, which means you'd be limited to only 2KHz of audio bandwidth. This is why they labeled it as a narrow-band replacement for the YK-88A.

Furthermore, there's a few other factors that come into play here. Remember that the TS-950SDX uses the DSP unit for both SSB and AM modulation. By default, the DSP will limit you to 3.1KHz of TX bandwidth on AM. If you use the power-on mod to enable 6KHz of bandwidth, that will only work on SSB unless you have a specially patched firmware. (There's an article in the modifications section which describes it.)

# I am able to switch both the HPF and LPF OFF on SSB and AM.

You said you have the latest firmware. You did not say if you had the patched firmware with the HiFi AM mod. There used to be a guy in eBay selling ready made EPROM chips that you could use to upgrade, but I don't think he's doing it anymore. I don't know if you obtained a chip or burned one yourself. If the latter, you can download the modified EPROM image from here:

http://people.freebsd.org/~wpaul/ts-950 ... patch.html

# I am awaiting information on the latest patch that the previous owner of the rig had done. I believe it is the one to which you inserted a link to.

Also, you can use the service menu to allow you to change both the 1st and 2nd IF filter settings for TX as well as RX. This includes setting the 2nd IF filter (8.83Mhz) to bypass, where the filtering is completely disabled. This in conjunction with the firmware mod above will give you the widest possible TX bandwidth (6KHz, basically the same as the radio's eSSB bandwidth).

# Oh, I didn’t think of the 2nd IF filter bypass. I would imagine that I can get to the right MENU by turning on the POWER while pressing the ENT key as per the Manual?

If you download the firmware patch file at the bottom of the page mentioned above, it contains a FAQ.txt file which explains how to change the service menu setting and enable the "off" setting in the LPF menu (for full HiFi mode).

# Appreciate the FAQ.txt file information 

Lastly, note that the 1st IF (455KHz) filter setting doesn't have a bypass (all off) position like the 2nd IF setting does. This setting actually has no effect on AM transmit, but it does affect AM receive. You can set it to 12Khz, which is not bad, but you can also easily create a bypass setting, as long as you don't mind giving up one of the extra narrow CW filter slots. Basically, you can connect a jumper wire in the place where the optional CW filter would go and just pretend it's a bypass setting. This will give you a little better bandwidth on RX. If you don't have the optional extra narrow CW filter in your rig, the slot is just sitting there unused anyway.

# I am thinking of replacing the 1.8kHz filter (I think it is the YK-88SN-1) at the 2nd IF with the Inrad 4 k filter.

# Oh, Inrad sent a one-pager about the install that I found confusing. It talks about cutting off "the last two pins flush to the white block" and also "removing small PC assembly." To remove the "PC assembly" I would need to unsolder four pads. Also, the picture of the filter doesn't jive with where those two pins that are supposed to be cut off sit?

# Let me know if what I am proposing above makes any sense?

Cheers!

JJ

BillPaul
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Post by BillPaul » Sun Aug 10, 2014 12:45 am

Okay, I guess I misunderstood. When you mentioned the AM filter, I thought you were interested in AM operation.

The way the SDX works, it comes from the factory with 6KHz and 2.7KHz filters pre-installed in the 2nd IF stage. The computer forces the use of the 2.7KHz filter on SSB on transmit, and that filter is wired in. You can replace it with the 4KHz INRAD filter, but it would take soldering.

However, you don't need to do that: you should just bypass the filter using the service mentu trick. Once you do that, you can bypass the 2nd IF filter entirely, or even use the 6KHz one if you want (the mod fixes things so that you can set the filters any way you want in TX, just like in RX).

The ENT key menu is not the service menu. It's the menu that lets you tell the radio which optional filters are plugged in. (The computer can't detect them automatically.)

To enter the service menu, press and hold the TX M.CH and SCAN buttons simultaneously while powering on the radio. Then rotate the small encoder knob to select menu option 01, and use the UP/DOWN keys to set it to "on" (default is off). Then press the CLR key to exit the menu. You will now be able to press the 8.33 and 455 buttons while transmitting to change the TX filter selection.

Note that the first thing that comes up when you enter the service menu is option 00, which shows you the firmware EPROM cheksum. It's four hexadeciman digits in the left of the display, in yellow. If you have my modded firmware, it will say 1d0c.

Without the modification, you can set the LPF menu option to "off" in AM mode, but the radio won't transmit. The little red "ON AIR" light comes on and some relays click, but there's no TX output signal. With the modded firmware, the radio will in fact transmit in AM mode with both HPF and LPF set to off, and you'll have 6KHz of audio bandwidth, just like on SSB.

So, basically, to get full TX bandwidth, you have to both set the HPF and LPF options right to configure the DSP _and_ you have to bypass the 2nd IF analog filters with the trick described above. Again, the 1st IF (455KHz) filters aren't used on TX for AM and SSB modes: the DSP handles it instead.

If you want full 6KHz bandwidth then you can stop right there. If you really want 4KHz bandwidth instead, then you can experiment a bit, both with using the 6KHz analog filter like I nentioned above, or by doing your own limiting at the audio level, maybe with an equalizer.

As for your audio setup, you'll probably find that with the front panel mic jack, your low end will be limited to about 80Hz. This is because the mic preamp is designed with a rolloff at around that point. (The microphones that Kenwood makes all bottom out at around 100Hz anyway.) This is where hardware modifications come in. The Voodoo TX mod feeds the audio direct to the DSP unit, bypassing the buiit-in preamp circuits so that you can get bass response all the way to 20Hz.

You should still get pretty good results though even with what you have, once you set up the filters correctly: the limits in the mic preamp don't affect the high end (treble) response. So you'll still exceed the 3KHz bandwidth of the TS-870.

-Bill, N1GPT
Last edited by BillPaul on Tue Aug 19, 2014 3:55 pm, edited 1 time in total.

BillPaul
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Posts: 66
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Post by BillPaul » Mon Aug 11, 2014 11:35 am

Oh, I almost forgot something. There's another menu setting which may be handy here.

If you look at the owner's manual, section 4-2-13, they describe the "Power ON" menu functions. These are basically preference settings which you normally don't need to change very often. You have to press and hold the MENU key while powering on the radio to access them.

Option 73, "Fil sel," allows you to change the behavior of the 8.83 and 455 analog filter selection keys. If the function is on (which it is by default), then the computer limits the filter selection choices: it only lets you choose settings that make sense for the current mode. For example, it doesn't let you select the 270Hz narrow CW filter position if you're in SSB mode (for obvious reasons: this is way too narrow a passband for voice).

If you turn this function off, then you can set the filters any way you choose, whether they make sense or not. You can enable the CW filters in SSB mode, or the SSB filters in CW mode, or whatever.

In conjunction with the service menu trick I described in my previous message, this also lets you select arbitrary filter configurations for TX too. You can even transmit in SSB through the 2nd IF CW filters if you want, not that whis would do you much good. :)

-Bill, N1GPT

JJ2013
Voodoo Audiophile
Posts: 141
Joined: Sat Apr 27, 2013 9:16 pm

INRAD 4 k filter

Post by JJ2013 » Mon Aug 11, 2014 2:51 pm

Hey Bill!

Sure am glad to get another message from you as you really know the 950SDX better than inside out and know it from analog and digital perspectives both!

OK on the additional how to enable even more filter combinations 8)

Now, below, see points & clarifications to your advice from before.

The EPROM checksum is: 1d0c :-)

Would you please comment on what I am writing below (as I am pretty obtuse I appears!)?
Received the 4 k Inrad filter. Their documentation is a bit confusing. Talks about removing the small PC assembly yet at the same time telling that no soldering is necessary! To remove the small PC assembly one would need to unsolder 4 pads, doesn't make sense. Also, tells about having to cut off two ground pins......Do I really need to cut off the GROUND PINS? Looking at their documentation it is confusing as to which ground pins I would need to cut off? With the "small PC assembly removed through unsoldering" there would not be any pins to cut off in the first place......

Pressing 8.33 and 455 buttons I see the following filters come on (assuming that no optional filter have been installed so that when it says 1.8 the filter would not actually be 1.8 k although one can probably tell based on what the audio on SSB sounds like......):

8.33
6k
2.7k
1.8k
"Nothing displayed" => would this be the 6.7 k TX bandwidth?

455
2.7k
500
250

In another post, I will also be asking about an SWR issue that I am seeing now!

Thanks again for not having "unsubscribed" to the slew of emails chock-full with infantile questions
:roll:

Cheers!

JJ

BillPaul
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Joined: Wed Jan 19, 2011 11:52 am

Post by BillPaul » Mon Aug 11, 2014 4:59 pm

Okay, in regards to the INRAD filter documentation, I'm not sure what's going on there.The photo shows that it's mounted on a plug-in board. The only reason I can think of to remove that board is if you wanted to mount the filter in place of one that's already soldered into the radio. Some rigs did require that filters be soldered in when installed. The TS-430 is an example: all of the optional filters (narrow SSB, narrow CW and AM) have to be soldered in. With the TS-940 I know the optional filters are pluggable.

In some cases the AM filter may be a factory standard one, in which case it would be soldered down and you'd need to remove the plug-in PC board from the INRAD replacement in order to put it in place of the original. The instructions they sent you may be general directions and might not necessarily apply to your particular installation scenario.

If you were going to use that filter, assuming it has the plug-in PC board already fitted, I would plug it into the slot meant for the optional YK-88SN-1 1.8KHz narrow SSB filter. It should fit in that slot. Then you can lie to the radio and tell it that the 1.8KHz filter is installed. You could then use the various menu tricks that have been discussed to get the rig to transmit through it.

But, like I said, I think it's redundant.You can already get the radio to bypass all of the 8.83MHz filters just with the menu tricks, and you don't even need to take the cover off.

As for the 8.83 and 455 buttons, yes, the "nothing displayed" case is the bypass position. When all the indicators are off it means all the filters are disengaged.

Your list is incomplete though. The full list is:

8.83
------
6K
2.7K
1.8K
500
270
[all off]

455
------
12K
6K
2.7K
500
250

Note that the 455KHz 1st IF filter selection doesn't have a bypass (all off) setting. What some people do is turn the 250Hz filter position as a makeshift bypass mode. The 250Hz filter is optional. What some people do is put a jumper wire in its place, and then set the radio up to think there's a filter installed in that slot. Then when you select the 250Hz position, you actually bypass everything.

This mod is documented here:

http://www.voodoo-labs.com/index/sdxmod ... termod.htm

A similar mod for the TS-850 is shown here:

http://www.cleanrf.com/ka0ka/photo21.html

For the TS-950SDX, this mod really only affects the receiver. In transmit mode, the DSP unit handles all of the 1st IF filtering for the AM and SSB modes, which you can configure using menus 20 and 21.

-Bill, N1GPT
Last edited by BillPaul on Tue Aug 12, 2014 3:28 pm, edited 1 time in total.

JJ2013
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Posts: 141
Joined: Sat Apr 27, 2013 9:16 pm

Post by JJ2013 » Tue Aug 12, 2014 1:33 pm

Hey Bill!!

I am starting to like the TS 950 SDX even more 8)

A really fabulous radio and it appears that I have to discover the myriad possibilities it provides!

Thank you again for very detailed and professional feedback!

Cheers!

JJ

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Post by Voodoo Guru » Tue Aug 19, 2014 12:29 am

Howdy Y'all,

Spot on advice and information as always Bill!!
Thanks for posting.
JJ, you will like the SDX more and more as you play with it.
Have Fun!
Take Care,
Voodoo Guru
From Deep in the IDD of the Sub-Harmonix Realm

JJ2013
Voodoo Audiophile
Posts: 141
Joined: Sat Apr 27, 2013 9:16 pm

Post by JJ2013 » Thu Aug 21, 2014 7:11 pm

Hi VooDoo Guru!

I likey the 950 SDX more and more 8) 8)

JJ

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