Telewave 44A how to add the sample port

[tropiradio]

Hope this will be ok to post here, as I could not find any other section that would deal specifically with wattmeters and/or the Telewave brand in itself. Since this is the section I usually post to, hope its appropriate. Otherwise please feel free to relocate.

I do have a 44A wattmeter and would like to get information on how the -40dB sample port is implemented at the factory to try and add one to my wattmeter to upgrade it to 44AP. Even some internal pictures of the unit showing the sampler port section would be useful. Assuming they use some sort of shielded broadband T attenuator, but I have searched up and down for this information and so far could not find anything. I mostly use VHF and UHF, so no need to design the sample port attenuator go any higher, although if I can build it to original specs it would be of course a plus.

Years ago I had a 44AP with the port already in place and always found it very useful to test among other things repeater desense and other measurements. Nowadays I mostly use the sampling T from my RF Industries adapter kit, but given it has variable attenuation depending on the plunger position, its a bit less convenient to use. Also have a small 65W dummy load that came with a separate sample connection that I got from a surplus parts sale, so there was no brand or model, much less datasheets with it. The port has about -40dB attenuation, but varies quite a bit (8-10dB) depending on frequency and band being tested.

Was thinking perhaps sending Telewave an email, but given that the 44AP model is now around 1.5K and up, imagine they would want a good chunk of cash for a retrofit sample port kit, if it even exists. So not sure the cost of a factory direct option would be justifiable.

Thanks in advance for any information.

 

[prcguy]

I don't have a sample port on my 44A either but am familiar with them in general. The internal line section is very similar to a Bird 43 as it takes up the entire width of the housing and there is no space for an additional sampler. You might check the telewave site and look for a manual with schematic diagram to see what they are doing. It could be something simple like tapping the same point that is rectified to feed the meter with a 1-2pf cap then off to a BNC connector.

Or you could just get a Bird sample port and use it stand alone. Those usually go for $75 around here but here is an expensive one on eBay.

Bird 4275-020 Variable RF Sampler 20-1000 MHz N-Type M/F | eBay

I have a used but good working Bird 4275-020 RF sampler for sale. I've owned this for about a year or so but am getting out of radio repair and selling off some of my bench. This will be sold as is with no returns. Any questions please ask.

www.ebay.com

 

[ramal121]

Looks like it come out of the middle of the directional coupler through a feed through cap and the coax from the BNC is soldered onto that.
I don't know if a non P model would have that hole and plugged.
I don't use mine. Always grab the aforementioned Bird sampler.

 

[tropiradio]

Thanks for the very useful picture, and mine of course neither has the feed-through nor the two screws on each side of it. Guess they build in some sort of sensing element inside the directional coupler. Was trying to figure out how to pull the directional coupler section out, and seems it has terminals beneath that are soldered into the pc board which seems to be held in place by the two meter studs and nuts, plus the two selector switches on the front panel.

So I'm guessing any factory upgrade would entail replacing the whole directional coupler along with whatever is in there to act as the sampling element.

 

[prcguy]

So I'm guessing any factory upgrade would entail replacing the whole directional coupler along with whatever is in there to act as the sampling element.

I would think so and modifying the stock directional coupler would be tricky and may affect accuracy across different frequency ranges.

 

[ramal121]

I would think you could drill a hole and mount some coax with a sniffer lead up inside but as prcguy mentioned a full calibration would probably be in order. All those blue pots look scary. At least without the manual and procedure. And this is the first time in 25 years I had the back off to see what's really inside.

 

[cavmedic]

Are the input connections the same as bird in relation to quick change?

If so, you could find a 4275 and install.

 

[cavmedic]

there is a Ham over on QTH.com ( K3DUA) that has a ton of Bird stuff for sale. I’ve bought many bird items from him over the past year.

K3DUA QTH.com search

 

[tropiradio]

Just (finally) received a reply from Telewave about adding the sampling port:

===================
We received your quest to change your meter to Model 44AP. It would be cheaper to buy a new unit then change the old one over.
If paid by credit card, you can get 30% off this offer is until the end of December 2023.

2023 $1,191.55 each
2024 $1,525.19 each

NOTE: this change you want to make can only be done on our site and can’t be changed in the field.
===================

Wow, with that generous discount almost feel like ordering two instead of just one!
Obviously they are not interested in selling me the directional coupler with the sample output, and then I would just need to recalibrate the unit to the original readings I had before the modification.

 

[davidgcet]

why not just make an iso-tee and use that? when i worked for my parent's MSS we made and used them for our older monitors that could not duplex gen. a tee with UHF females on the straight ends and a UHF Male (pl259) on the short side is all that is needed. unscrew the male center pin, grind it down to the flange then screw it back in. put a small piece of tape over it so it cannot touch accidentally and you have a pretty good isolator. it is easy enough to figure out the isolation by comparing the level out the iso tee side port with that out the ends and doing the math. typically we saw about 40 db which was more than enough to keep from damaging the generator or spectrum analyzer.

 

[tropiradio]

why not just make an iso-tee and use that? when i worked for my parent's MSS we made and used them for our older monitors that could not duplex gen. a tee with UHF females on the straight ends and a UHF Male (pl259) on the short side is all that is needed. unscrew the male center pin, grind it down to the flange then screw it back in. put a small piece of tape over it so it cannot touch accidentally and you have a pretty good isolator. it is easy enough to figure out the isolation by comparing the level out the iso tee side port with that out the ends and doing the math. typically we saw about 40 db which was more than enough to keep from damaging the generator or spectrum analyzer.

Hi yes definitively not worth messing with the internals of this wattmeter if Telewave will not cooperate, let alone baing economically feasable with these prices they quoted. I already have a 65W snad alone dummy load that has a build in -40dB sampling port and use it, but just wanted to see if I could get something more integrated. I used to have a 44AP and its sample port always came in handy, but that was years ago and now only have a 44A. I also have an adjustable sampling Tee but its a bit of a pain having to set the attenuation by sliding the piston in and out everytime one needs to use it. Oh well yes its still better than nothing, and being ajustable is sometimes a plus.

Even with a service monitor with duplex capability you sometimes still will need a sample/injection port to for example be able to check for repeater receiver desense when Tx is on after the duplexer (antenna port) which is only a single port for both measuring Tx out and to inject a Rx signal into the same port which is where a sample port comes in handy. This also allows you to fine tune the duplexer reject adjustments for optimum settings against the actual Tx carrier of the repeater and/or Tx noise.

 

[prcguy]

Hi yes definitively not worth messing with the internals of this wattmeter if Telewave will not cooperate, let alone baing economically feasable with these prices they quoted. I already have a 65W snad alone dummy load that has a build in -40dB sampling port and use it, but just wanted to see if I could get something more integrated. I used to have a 44AP and its sample port always came in handy, but that was years ago and now only have a 44A. I also have an adjustable sampling Tee but its a bit of a pain having to set the attenuation by sliding the piston in and out everytime one needs to use it. Oh well yes its still better than nothing, and being ajustable is sometimes a plus.

Even with a service monitor with duplex capability you sometimes still will need a sample/injection port to for example be able to check for repeater receiver desense when Tx is on after the duplexer (antenna port) which is only a single port for both measuring Tx out and to inject a Rx signal into the same port which is where a sample port comes in handy. This also allows you to fine tune the duplexer reject adjustments for optimum settings against the actual Tx carrier of the repeater and/or Tx noise.

Instead of a simple iso-tee type sample port its best to use a directional coupler and its nice to have it in the full duplex line after the duplexer. That means it needs to handle the full transmit power of whatever your testing. I often use a Bird 43 with optional directional coupler sample slug for this but you have to find one with a frequency range that you need.

BIRD 1 KW SLUG 225-400 DIRECTIONAL COUPLER ELEMENT FOR BIRD 43 - 225 TO 450 MHz | eBay

Power 1 KW. Frequency 225 TO 450 MHz. WHAT YOU SEE IN THE PICTURE IS WHAT YOU WILL OBTAIN. We encourage you to read THE FOLLOWING ! WE HAVE PROCEEDED TO CHECK OUT AND HAVE CALCULATED.

www.ebay.com

You can also pick up a low power directional coupler for use in the rx only line and 20dB coupling factor is a good goal. I do see a 15dB version on eBay that is a reasonable price, although you would have to use adapters or make up a set of SMA cables for it.

Mini-Circuits ZFDC 15-5 Coaxial Directional Coupler 50Ω 1-2000 MHz | eBay

Coaxial Directional Coupler. Coupling, Nominal: 15.5 ±0.5 dB. Coupling, Flatness: ±1.0 dB. Frequency: 1 to 2000 MHz. 50Ω 1-2000 MHz. Directivity, Upper Range: 18 dB Typ., 11 dB Min. Directivity, Mid Range: 25 dB Typ., 20 dB Min.

www.ebay.com

 

[tropiradio]

Instead of a simple iso-tee type sample port its best to use a directional coupler and its nice to have it in the full duplex line after the duplexer. That means it needs to handle the full transmit power of whatever your testing. I often use a Bird 43 with optional directional coupler sample slug for this but you have to find one with a frequency range that you need.

https://www.ebay.com/itm/201932712124

You can also pick up a low power directional coupler for use in the rx only line and 20dB coupling factor is a good goal. I do see a 15dB version on eBay that is a reasonable price, although you would have to use adapters or make up a set of SMA cables for it.

https://www.ebay.com/itm/225734659066

I have two directional couplers, one from Mini Circuits very similar to the one you pictured (mine is a zfdc-20-5+) and an IFR AC4101 Return Loss Bridge. Problem is none of those can handle any serious power to check repeater desense under real operating conditions. The IFR can only take 5W, and the Mini Circuits probably only a few milliwatts.

Can't do much with one of those Bird slugs, never been a big fan of carrying around all those "stoppers", that is why I prefer the Telewave wattmeter. I know the Bird will be more accurate according to each slug's frequency range and power, but on field trips absolute accuracy is usually not that critical, and the less extra stuff one has to carry the better. And unless you bring them all, chances are one usually will need the one stopper that you forgot to bring or though you would absolutely not need.

PS. when you want to copy and paste any ebay item link, no need to bring along all the endless tracking clutter they add to their links. Just cut it off after the ".../itm/1234567890123" (actual item number) and that will do it, just as I shorted those links above.

 

[mastr]

Just (finally) received a reply from Telewave about adding the sampling port:

...NOTE: this change you want to make can only be done on our site and can’t be changed in the field...

I wouldn't be too happy with that reply. I am generally offended when others presume to know what I am or am not capable of.

 

[tropiradio]

I wouldn't be too happy with that reply. I am generally offended when others presume to know what I am or am not capable of.

That reply came from sales, so one perhaps may assume, strangely as it may be and giving them a bit the benefit of the doubt, that the person replying might not be too technically knowledgeable, possibly doing its best within their limited understanding and just parroting what they where told to say. I think not worth giving it too much thought... oh well it is what it is, just move on.

 

[davidgcet]

an isotee is perfect for what you want, all power goes to the meter and load and the isolated side lets you inject or sample as desired. used them many times to check desense. gen csq and put the repeater in monitor, adjust for 20db sinad then pop on the pl/dpl and listen for desense. if you have a sinadder you can cheat and not use your ears, but i rarely used ours after the first year or so of doing it because i learned to hear even the slightest desense.

here is a hint, if you know your 20db quiet point thru the duplexer you can then hook up the isotee and see exactly how much isolation/attenuation it has. like i said, most will be in the 40 to 46 db range.

as far as telewave or bird is concerned, each has its use. i had both an much preferred my telewave to a bird until we primarily started working on 800 mhz stuff. then you had to use the chart on the back to figure the correct readings. at that point i went back to a bird and a handful of slugs. had we not had to deal with 800 so much i would have stuck with the telewave as they are great units.

 

[prcguy]

an isotee is perfect for what you want, all power goes to the meter and load and the isolated side lets you inject or sample as desired. used them many times to check desense. gen csq and put the repeater in monitor, adjust for 20db sinad then pop on the pl/dpl and listen for desense. if you have a sinadder you can cheat and not use your ears, but i rarely used ours after the first year or so of doing it because i learned to hear even the slightest desense.

here is a hint, if you know your 20db quiet point thru the duplexer you can then hook up the isotee and see exactly how much isolation/attenuation it has. like i said, most will be in the 40 to 46 db range.

as far as telewave or bird is concerned, each has its use. i had both an much preferred my telewave to a bird until we primarily started working on 800 mhz stuff. then you had to use the chart on the back to figure the correct readings. at that point i went back to a bird and a handful of slugs. had we not had to deal with 800 so much i would have stuck with the telewave as they are great units.

I've been working with a few other repeater owners and have been taking more and more equipment to sites so we can cover just about any desense issue. This includes a Telewave 44A for basic fwd/ref power measurements, a Bird 43 with various slugs including directional coupler slug for use in the high power full duplex path for receive injection, a low power dual directional coupler for receive injection and a 100w 30dB attenuator to run long key down full duplex tests without abusing my service monitor. Then there is the HP 8920A service monitor and an HP 8594E spectrum analyzer with tracking generator for testing or aligning duplexers and filters.

I usually pack various band pass filters like 1/4 wave cavities, multi section window filters and circulators to sprinkle around when chasing problems to see if they have any affect on a problem. And a couple of high isolation power dividers to put in the rx line so a spectrum analyzer can see what the receiver is hearing looking for interference. Then there are the cables, lots of double shield cables in case a bad one is found or we have to move some components around and lengthen cables.

If I had a sample port in my 44A I'm not sure it would get much use compared to other sample or inject items I carry.

 

[tropiradio]

an isotee is perfect for what you want, all power goes to the meter and load and the isolated side lets you inject or sample as desired. used them many times to check desense. gen csq and put the repeater in monitor, adjust for 20db sinad then pop on the pl/dpl and listen for desense. if you have a sinadder you can cheat and not use your ears, but i rarely used ours after the first year or so of doing it because i learned to hear even the slightest desense.

Yeah I've gotten used to use my ears as well for that. Turn off the 1KHz modulation, set signal level to where it gets a bit critical in terms of noise, but not too low so that noise is too high to let you notice any subtle changes, or too little noise. Then key/unkey repeater by enabling or disabling PL on the generator (or external mike if available) and listen to aspect changes, and as any desense improvements are made (lower noise level) readjust your signal level to get back to making the noise level critical again. And so on until no further improvements can be made. Depending on the repeater being used, sometimes on Sinclair duplexers that where already correctly tuned for the frequencies to be used I've found that adjusting the reject trimmer tiny bit on the Tx side will give the most improvement. That is when that last bit of interfering Tx noise gets hammered out.

 

[tropiradio]

I've been working with a few other repeater owners and have been taking more and more equipment to sites so we can cover just about any desense issue. This includes a Telewave 44A for basic fwd/ref power measurements, a Bird 43 with various slugs including directional coupler slug for use in the high power full duplex path for receive injection, a low power dual directional coupler for receive injection and a 100w 30dB attenuator to run long key down full duplex tests without abusing my service monitor. Then there is the HP 8920A service monitor and an HP 8594E spectrum analyzer with tracking generator for testing or aligning duplexers and filters.

I usually pack various band pass filters like 1/4 wave cavities, multi section window filters and circulators to sprinkle around when chasing problems to see if they have any affect on a problem. And a couple of high isolation power dividers to put in the rx line so a spectrum analyzer can see what the receiver is hearing looking for interference. Then there are the cables, lots of double shield cables in case a bad one is found or we have to move some components around and lengthen cables.

What you don't take with you is what you will need. Been there done that. and lesson learned a long time ago.

If I had a sample port in my 44A I'm not sure it would get much use compared to other sample or inject items I carry.

With that other 44AP back when I was just using the sample port because it was already there and seemed convenient and worked well, so had gotten used to have it.

 

[prcguy]

What you don't take with you is what you will need. Been there done that. and lesson learned a long time ago.

I forgot to mention I keep lock picks and bump keys in my truck due to the times a site owner handed out the wrong keys to the mountain top site. Not fun after driving 75mi and up nasty dirt roads to get to the site, only to find the keys don’t work.