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Re: VHF MTR2000 Poor Receive Performance

 

Yes, if those are the factory supplied cables (and Tees) and the desired frequency is within the factory specified range then something else is likely the issue. But if, as is common on this group, he's trying to use a set of cavities made for public service down in the ham band then the cables are probably incorrect.

I haven't been paying 100% attention to everything said in this thread. I was generally trying to share some of my own understanding and experience, when making a set of cables for a set of used cavities which did not come with them, with those who might want it. If anything I said was incorrect please illuminate us all.
On Monday, October 31, 2022, 11:29:11 AM CDT, Teton Amateur Radio Repeater Association (TARRA) <tarra@...> wrote:


Sounds to me like you don't know what you are talking about with this
duplexer. Leave the cables alone. This duplexer is designed for the
cables to be used for the full frequency range specified for this duplexer.

Mick - W7CAT

----- Original Message -----
From: "Bradley Andrews via groups.io"
Sent: Monday, October 31, 2022 10:12:44 AM
Subject: Re: [repeater-builder] VHF MTR2000 Poor Receive Performance

>
> Sounds to me like your inter-cavity cables aren't close enough to the
right length.
>
> You probably already know this but I'll state it for those who might
not:
> The reason the cable length is pretty critical for proper performance
is the impedance transformation property of a 1/4 wavelength line. OK
that's the general statement but here's the detail:
>
> If you look at an individual cavity on a VNA, you'll see the expected
50 ohm sweet spot at the pass frequency. The RF flowing in the 50 ohm
cable passes through with no reflection. But at the notch frequency, it
will be very close to a perfect short or a perfect open. (Which it is
depends on the design of the notch mechanism on the cavity and whether
the notch is above or below the pass freq.)
>
> For the sake of our example, let's assume that your cavity exhibits a
short at the notch freq.
>
> That 1/4 wave cable between cavities transforms that short so that at
the other cavity it looks like almost an open circuit. But the other
cavity is also presenting a short-circuit impedance - being driven by
the open circuit impedance at the cable. So the mismatch is about as
perfect as you can get (or you can also say, the match is about as
imperfect as you can get) and very, very little energy gets transferred.
That's why a set of cavities with the correct cable lengths shows a
greater notch depth than the sum of the individual cavities. Those
additional mismatches contribute significantly to the notch depth.
>
> Back to your case: The approx. 90 dB notch depth you're measuring is
only the sum of the cavities' individual notches. You're not benefitting
from the cable mismatches.
>
> As many have alluded to, unfortunately it's not as easy as just
cutting a set of 1/4 wave cables. There is a certain small but
significant amount of 'effective length' in the coupling loop, whose
effective amount varies with the coupling set and the notch spacing. So
your cables are going to be shorter than 1/4 wave from connector to
connector - the rest of the 1/4 wave is 'absorbed' in the coupling loop.
>
> If you're very clever you could probably measure the reactances at
the notches with your VNA then calculate how short to cut your cables.
That will give you some idea what ballpark you're in. I've tried to do
that and either I wasn't quite clever enough or Murphy was having his
fun that day (probably both) and I still had to resort to 'empirical'
methods to find the optimum cable length.
>
> I sure learned a lot though!
>
> 73
> Brad KB9BPF
> On Monday, October 31, 2022, 10:42:22 AM CDT, Jared Smudde wrote:
>
> I went ahead and tried to work on the receive/high pass side. All 3
cavities were already at their best return loss from when I was working
on it the other day. So I went ahead and tuned the notches to a 600KHz
split and rotated the loops to get 0.4DB IL per cavity and adjusted the
notches back to 600KHz and got 31DB out of the notches. When I called
the receive side together, I had almost 7db of insertion loss at the
receiver frequency and the notch was way off of where it should have
been. Using the notch screws on the 2 cavities closest to the antenna
port, I was able to adjust the notch to where it belongs and was getting
90db of notch. However, when I adjusted the 3rd notch screw on the
cavity where the receiver connects, all that did was adjust the
insertion loss on the pass. I adjusted it to 1.45db of IL and 90db of
notch.
>
> Is that right though? I would have expected the 3rd notch screw to
also adjust the notch and not the insertion loss on the pass.
>
>
>
>
>
>
--
Untitled Document
Re: VHF MTR2000 Poor Receive Performance

 

Good point, Eric.

When I was messing around with cavities I found best results when I cranked the VNA's source power up all the way. I don't remember but I think it went to something like +10 or +15 dBm. I think default was around 0 dBm so that gave me an extra 10 - 15 dB of measurement range.

73
Brad
On Monday, October 31, 2022, 11:25:01 AM CDT, Eric <vzwengr@...> wrote:


Is a notch depth greater than 90bB exceeding the capabilities of the test equipment?

Eric
Re: VHF MTR2000 Poor Receive Performance

 

Sounds to me like you don't know what you are talking about with this duplexer. Leave the cables alone. This duplexer is designed for the cables to be used for the full frequency range specified for this duplexer.

Mick - W7CAT

----- Original Message -----
From: "Bradley Andrews via groups.io"
To: [email protected]
Sent: Monday, October 31, 2022 10:12:44 AM
Subject: Re: [repeater-builder] VHF MTR2000 Poor Receive Performance


Sounds to me like your inter-cavity cables aren't close enough to the
right length.

You probably already know this but I'll state it for those who might
not:
The reason the cable length is pretty critical for proper performance
is the impedance transformation property of a 1/4 wavelength line. OK that's the general statement but here's the detail:

If you look at an individual cavity on a VNA, you'll see the expected
50 ohm sweet spot at the pass frequency. The RF flowing in the 50 ohm cable passes through with no reflection. But at the notch frequency, it will be very close to a perfect short or a perfect open. (Which it is depends on the design of the notch mechanism on the cavity and whether the notch is above or below the pass freq.)

For the sake of our example, let's assume that your cavity exhibits a
short at the notch freq.

That 1/4 wave cable between cavities transforms that short so that at
the other cavity it looks like almost an open circuit. But the other cavity is also presenting a short-circuit impedance - being driven by the open circuit impedance at the cable. So the mismatch is about as perfect as you can get (or you can also say, the match is about as imperfect as you can get) and very, very little energy gets transferred. That's why a set of cavities with the correct cable lengths shows a greater notch depth than the sum of the individual cavities. Those additional mismatches contribute significantly to the notch depth.

Back to your case: The approx. 90 dB notch depth you're measuring is
only the sum of the cavities' individual notches. You're not benefitting from the cable mismatches.

As many have alluded to, unfortunately it's not as easy as just
cutting a set of 1/4 wave cables. There is a certain small but significant amount of 'effective length' in the coupling loop, whose effective amount varies with the coupling set and the notch spacing. So your cables are going to be shorter than 1/4 wave from connector to connector - the rest of the 1/4 wave is 'absorbed' in the coupling loop.

If you're very clever you could probably measure the reactances at
the notches with your VNA then calculate how short to cut your cables. That will give you some idea what ballpark you're in. I've tried to do that and either I wasn't quite clever enough or Murphy was having his fun that day (probably both) and I still had to resort to 'empirical' methods to find the optimum cable length.

I sure learned a lot though!

73
Brad KB9BPF
On Monday, October 31, 2022, 10:42:22 AM CDT, Jared Smudde wrote:

I went ahead and tried to work on the receive/high pass side. All 3
cavities were already at their best return loss from when I was working on it the other day. So I went ahead and tuned the notches to a 600KHz split and rotated the loops to get 0.4DB IL per cavity and adjusted the notches back to 600KHz and got 31DB out of the notches. When I called the receive side together, I had almost 7db of insertion loss at the receiver frequency and the notch was way off of where it should have been. Using the notch screws on the 2 cavities closest to the antenna port, I was able to adjust the notch to where it belongs and was getting 90db of notch. However, when I adjusted the 3rd notch screw on the cavity where the receiver connects, all that did was adjust the insertion loss on the pass. I adjusted it to 1.45db of IL and 90db of notch.

Is that right though? I would have expected the 3rd notch screw to
also adjust the notch and not the insertion loss on the pass.




--
Untitled Document
Re: VHF MTR2000 Poor Receive Performance

 

Is a notch depth greater than 90bB exceeding the capabilities of the test equipment?

Eric
Re: VHF MTR2000 Poor Receive Performance

 


Sounds to me like your inter-cavity cables aren't close enough to the right length.

You probably already know this but I'll state it for those who might not:
The reason the cable length is pretty critical for proper performance is the impedance transformation property of a 1/4 wavelength line. OK that's the general statement but here's the detail:

If you look at an individual cavity on a VNA, you'll see the expected 50 ohm sweet spot at the pass frequency. The RF flowing in the 50 ohm cable passes through with no reflection. But at the notch frequency, it will be very close to a perfect short or a perfect open. (Which it is depends on the design of the notch mechanism on the cavity and whether the notch is above or below the pass freq.)

For the sake of our example, let's assume that your cavity exhibits a short at the notch freq.

That 1/4 wave cable between cavities transforms that short so that at the other cavity it looks like almost an open circuit. But the other cavity is also presenting a short-circuit impedance - being driven by the open circuit impedance at the cable. So the mismatch is about as perfect as you can get (or you can also say, the match is about as imperfect as you can get) and very, very little energy gets transferred. That's why a set of cavities with the correct cable lengths shows a greater notch depth than the sum of the individual cavities. Those additional mismatches contribute significantly to the notch depth.

Back to your case: The approx. 90 dB notch depth you're measuring is only the sum of the cavities' individual notches. You're not benefitting from the cable mismatches.

As many have alluded to, unfortunately it's not as easy as just cutting a set of 1/4 wave cables. There is a certain small but significant amount of 'effective length' in the coupling loop, whose effective amount varies with the coupling set and the notch spacing. So your cables are going to be shorter than 1/4 wave from connector to connector - the rest of the 1/4 wave is 'absorbed' in the coupling loop.

If you're very clever you could probably measure the reactances at the notches with your VNA then calculate how short to cut your cables. That will give you some idea what ballpark you're in. I've tried to do that and either I wasn't quite clever enough or Murphy was having his fun that day (probably both) and I still had to resort to 'empirical' methods to find the optimum cable length.

I sure learned a lot though!

73
Brad KB9BPF
On Monday, October 31, 2022, 10:42:22 AM CDT, Jared Smudde <computerwhiz02@...> wrote:


I went ahead and tried to work on the receive/high pass side. All 3 cavities were already at their best return loss from when I was working on it the other day. So I went ahead and tuned the notches to a 600KHz split and rotated the loops to get 0.4DB IL per cavity and adjusted the notches back to 600KHz and got 31DB out of the notches. When I called the receive side together, I had almost 7db of insertion loss at the receiver frequency and the notch was way off of where it should have been. Using the notch screws on the 2 cavities closest to the antenna port, I was able to adjust the notch to where it belongs and was getting 90db of notch. However, when I adjusted the 3rd notch screw on the cavity where the receiver connects, all that did was adjust the insertion loss on the pass. I adjusted it to 1.45db of IL and 90db of notch.

Is that right though? I would have expected the 3rd notch screw to also adjust the notch and not the insertion loss on the pass.

Re: VHF MTR2000 Poor Receive Performance

 

I went ahead and tried to work on the receive/high pass side. All 3 cavities were already at their best return loss from when I was working on it the other day. So I went ahead and tuned the notches to a 600KHz split and rotated the loops to get 0.4DB IL per cavity and adjusted the notches back to 600KHz and got 31DB out of the notches. When I called the receive side together, I had almost 7db of insertion loss at the receiver frequency and the notch was way off of where it should have been. Using the notch screws on the 2 cavities closest to the antenna port, I was able to adjust the notch to where it belongs and was getting 90db of notch. However, when I adjusted the 3rd notch screw on the cavity where the receiver connects, all that did was adjust the insertion loss on the pass. I adjusted it to 1.45db of IL and 90db of notch.

Is that right though? I would have expected the 3rd notch screw to also adjust the notch and not the insertion loss on the pass.
Re: UHF Cans?

 

Telewave VHF Bandpass. Nice grab!!!

Jim.

On Oct 31, 2022, at 6:52 AM, Jim W7RY via groups.io <jimw7ry@...> wrote:

?They are Telewave VHF pass cans. Most likely from a Telewave VHF transmit combiner.

Most older wide space transmit combiners used simple pass cavities.

73, Jim W7RY


On 10/31/2022 8:21 AM, Tedd Doda wrote:
Can someone identify these cans? They are 24" tall and
10" in diameter. Both loops have "insertion loss" adjustments
but no marking other than that.

I haven't sweep one yet. Bench is a little full.

Thanks,

Tedd, VE3TJD



--
Thanks and 73, Jim W7RY
Connecting Yaesu DR2X Repeater to Raspberry Pi/Allstar?

Chris Smart
 

¿ªÔÆÌåÓý

Someone asked me yesterday how to connect an Allstar node to a yaesu DR2X repeater, and mentioned they would like something plug-and-play. Is the best option?

That page mentions the DR1X. Will it work as well with the 2X?

?

Do we also need

?

Thank you in advance for any suggestions.

?

73,

Chris

?

?
Re: UHF Cans?

 

On 2022-10-31 9:56 a.m., Jeff DePolo WN3A wrote:
Telewave pass cavities, could be either VHF or UHF (3/4 wave)
depending on which loops are in them.

Jeff, I've attached a picture of the loop. From the connector
to the end of the loop is 1.25" and about 1/2" wide.

I've always used Sinclair equipment, so just wondering if
these have any usable value.

Tedd, VE3TJD

Loop.jpg

Re: UHF Cans?

 

Can someone identify these cans? They are 24" tall and
10" in diameter.
Telewave pass cavities, could be either VHF or UHF (3/4 wave) depending on which loops are in them.

--- Jeff WN3A




--
This email has been checked for viruses by Avast antivirus software.
www.avast.com
Re: UHF Cans?

Jim W7RY
 

Not 900 MHz at 24 inches in length.

Jim W7RY

On 10/31/2022 8:23 AM, Don Clark wrote:
They look like the ones used on 900 Mhz paging transmitters. Probably tuned around 928 - 932 Mhz. Will handle a lot of power.


On 10/31/2022 8:21 AM, Tedd Doda wrote:
Can someone identify these cans? They are 24" tall and
10" in diameter. Both loops have "insertion loss" adjustments
but no marking other than that.

I haven't sweep one yet. Bench is a little full.

Thanks,

Tedd, VE3TJD






--
Thanks and 73, Jim W7RY
Re: UHF Cans?

Jim W7RY
 

They are Telewave VHF pass cans. Most likely from a Telewave VHF transmit combiner.

Most older wide space transmit combiners used simple pass cavities.

73, Jim W7RY

On 10/31/2022 8:21 AM, Tedd Doda wrote:
Can someone identify these cans? They are 24" tall and
10" in diameter. Both loops have "insertion loss" adjustments
but no marking other than that.

I haven't sweep one yet. Bench is a little full.

Thanks,

Tedd, VE3TJD



--
Thanks and 73, Jim W7RY
Re: UHF Cans?

 

They look like the ones used on 900 Mhz paging transmitters. Probably tuned around 928 - 932 Mhz. Will handle a lot of power.

On 10/31/2022 8:21 AM, Tedd Doda wrote:
Can someone identify these cans? They are 24" tall and
10" in diameter. Both loops have "insertion loss" adjustments
but no marking other than that.

I haven't sweep one yet. Bench is a little full.

Thanks,

Tedd, VE3TJD
UHF Cans?

 

Can someone identify these cans? They are 24" tall and
10" in diameter. Both loops have "insertion loss" adjustments
but no marking other than that.

I haven't sweep one yet. Bench is a little full.

Thanks,

Tedd, VE3TJD

UHF cans.jpg

Re: CDM1250 For Winlink

 

Many people are using the RIM-Maxtrac 9600 with CDM series radios for Winlink, both packet (1200 and 9600) and Vara FM (Narrow and Wide). Many Winlink Gateways are also using this configuration. The only programming requirement is to set the TX audio to flat. If you do not use the "9600" version, make note of the information on the Repeater Builders website regarding unexpected volume commands.

The RIM-Alinco is also a popular solution for Winlink users that have the Alinco DR-x35 series radios.

-Scott, NS7C
Re: CDM1250 For Winlink

 

The RIM Maxtrac and the RIM Alinco are the soundcards that connect your radio to your computer. I do not know for sure but you may be able to use them with Winlink. They are designed to be used with Allstar

You will have to use a program such as Soundmodem or Direwolfe to use as a software TNC to allow Winlink to use the RIM devices to put the signal to the radios. I have not heard of anyone using the RIM devices to do Winlink but would be interested to see if it works. Let us know your results if you go through with it

Les Keegan?
N4LPK?

On Sunday, October 30, 2022 at 06:54:31 PM EDT, SCOTT READ <southbfd@...> wrote:


Looking for information. I have a Motorola CDM1250 and all the programming software and cable.? I am looking at buying the RIM-Maxtrac.? Is this plug and play or what do I have to do. I also have a Alinco DR-135T looking to do the same but with the RIM-ALinco.? Any help would be great on product.?

Thanks

Scott Read - KM6RFB
southbfd@...

Re: RF Harris Portables

 

I am going to pass on them as I have TMRD (too many radios disease). You should be able to find a collector that would want them. I am surprised that there are no pictures or articles about them. I must have had a manual back in 1980's when I worked on them. Probably gave it to the owner of the radios.
--
The Real RFI-EMI-GUY
Re: VHF MTR2000 Poor Receive Performance

 

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  • I appreciate the write up Jeff! I¡¯ll tune them up based on this and see if anything changes.

Kevin sent me a private email which reminded me you had a Q2330E (six-cavity).? For some reason I was thinking you had a Q2220E (four cavity).? For the Q2330E, target 0.4 dB loss per cavity, not 0.6 dB.? 0.6 dB would be right for a Q2220E.

?

??????????????????????????????????????????????????????????????????????????????? --- Jeff WN3A

?


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Re: Somewhat OT... imaging a hard drive...

 

Yup - CloneZilla is not persnickety about which OS is on which drive. Its partition to partition function may be a bit tricky, but drive to drive is excellent and fast.? Just saved my Server 2016 system getting off it's temporary USB boot drive to an internal SSD - whew.

IT has been my paying alter-ego for decades... almost nothing I can't make a PC or OS do.? Just made up two legacy dual-boot DOS and XP laptops for a regional radio shop to keep up service for legacy rigs.? Then ask me about USB-RS-232 adapters...

?
Re: VHF MTR2000 Poor Receive Performance

 

¿ªÔÆÌåÓý

Measure test cable losses by replacing the tee with a female-female barrel, then correct your insertion loss measurements based on that value when you¡¯re adjusting the coupling with the tee connected to the cavity and test cables.

?

0.35 dB is pretty light.? You¡¯d basically end up with notch cavities with little in the way of a bandpass characteristic at such light coupling (i.e. less out-of-band rejection, less mid-band rejection).? 0.5 to 0.6 dB per cavity should yield a good balance and still net you 100+ dB of notch depth.

?

??????????????????????????????????????????????????????????????????????????????????????????????? --- Jeff WN3A

?

From: [email protected] <[email protected]> On Behalf Of Jared Smudde
Sent: Sunday, October 30, 2022 7:54 PM
To: [email protected]
Subject: Re: [repeater-builder] VHF MTR2000 Poor Receive Performance

?

I appreciate the write up Jeff! I¡¯ll tune them up based on this and see if anything changes.

I know I have each cavity currently set to 0.35db IL.

I have an Amphenol Tee connector I¡¯m using. Now, do I need to normalize the SA cables with the Tee connector in line before measuring? That¡¯s what I¡¯ve been doing when messing with this.


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