TX Board for Motorola XPR8300 Repeater?
I am resurrecting an XPR8300. The TX board is scorched.?
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Board #:
MOTOTRBO U1-HP
8486777Z14-C
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UHF Ham Range
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Does anyone have a parted-out XPR8300 willing to sell the TX board to me?
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The poor heat-dissipation design makes this a seemingly common ailment.
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Private message me.
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Thanks,
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Steve, N9ATO
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Re: Improving selectivity on a reciver
Steven,
Receivers provide "selectivity" at various stages - and each have different purposes.
The front-end is selective, and operates at the fundamental operating frequency.? The front-end filtering is generally narrower than the whole band - depending on the type of filtering that's used.? Hamtronics receiver used helical resonators and L/C tuned circuits depending on the model.? Therefore - a receiver generally doesn't pass the entire 220-225 MHz range even if the receiver was built to cover this entire range.? Front-end selectivity is necessary to provide rejection to nearby signals - a few to several MHz away from the operating frequency.? Without front-end filtering - a receiver can be driven into overload easily from other signal sources.
The receiver's first I-F frequency is 10.7 MHz and provides a basic width of the intermediate frequency for two-way radio.? The receivers second I-F is 455 kHz and provides the final selectivity.? These filters determine how well a receiver will tolerate a signal on an adjacent channel that's 15 - 20kHz away or more.? Neither of these filters have anything to do with how wide the front-end is.
My question to you is - what are you wanting to accomplish?? Or, what is the problem that you feel narrowing something is going to help?
Kevin W3KKC
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On 4/8/2025 2:28 PM, steven harvey wrote: Hello Everyone,
Let me first say this is an experimental improvement to see it will work.? ? I have a hamtronics reciver board that is running in the 220MHZ space.? ? ?It's one the last board produced before the owner had a fatal bicycle accident.
I wanted to see if I could improvement the selectivity of the receiver by narrowing filters or am I look at more of a total redo of the circuit.? Like I said, I'm doing this as a experiment.
I wanted to narrow it to the current 222-225 Mhz from the old 220 to 225 Mhz.
Any suggestions would be helpful.
Thanks
Steven H.
N8RLW
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Re: Improving selectivity on a reciver
On 4/8/2025 2:46 PM, Mike via groups.io wrote: Never mind, I looked it up and its a custom 10.7MHz crystal filter using four discreet crystals. If you have the equipment you could sweep it for response then shop for a packaged filter with better specs. I don't see any adjustment or matching on the filter output to the receiver IC so its hard to say how well a drop in filter will perform but it may not be too bad. The OP has inquired how to improve input selectivity - not I-F selectivity.? Go back and re-read the inquiry. Kevin W3KKC
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Re: Improving selectivity on a reciver
Never mind, I looked it up and its a custom 10.7MHz crystal filter using four discreet crystals. If you have the equipment you could sweep it for response then shop for a packaged filter with better specs. I don't see any adjustment or matching on the filter output to the receiver IC so its hard to say how well a drop in filter will perform but it may not be too bad.
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Re: Improving selectivity on a reciver
Can you post the current IF filter mfr and model #??
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Re: Improving selectivity on a reciver
Your helicals should already be much narrower than that.?? What problem are we trying to solve?
Andy Zorca WJ9J
Hello Everyone,
?
Let me first say this is an experimental improvement to see it will work.? ? I have a hamtronics reciver board that is running in the 220MHZ space.? ? ?It's one the last board produced before the owner had a fatal bicycle accident.? ??
?
I wanted to see if I could improvement the selectivity of the receiver by narrowing filters or am I look at more of a total redo of the circuit.? Like I said, I'm doing this as a experiment.?
?
I wanted to narrow it to the current 222-225 Mhz from the old 220 to 225 Mhz.? ?
?
Any suggestions would be helpful.?
?
Thanks
Steven H.
N8RLW?
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Improving selectivity on a reciver
Hello Everyone,
?
Let me first say this is an experimental improvement to see it will work.? ? I have a hamtronics reciver board that is running in the 220MHZ space.? ? ?It's one the last board produced before the owner had a fatal bicycle accident.? ??
?
I wanted to see if I could improvement the selectivity of the receiver by narrowing filters or am I look at more of a total redo of the circuit.? Like I said, I'm doing this as a experiment.?
?
I wanted to narrow it to the current 222-225 Mhz from the old 220 to 225 Mhz.? ?
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Any suggestions would be helpful.?
?
Thanks
Steven H.
N8RLW?
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Re: Duplexer for amateur 70-cm band
Basic NOTCH ONLY duplexer.
Yes you can get -80+ with careful tuning.
Very popular with most two-way shops that are selling simple on-site systems.
Milt
N3LTQ
Quoting "Karl Shoemaker via groups.io" <srg734@...>:
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Anyone know if this is an okay one for 5 MHz spilt? ? I need at least 80db of notch (isolation) Supposedly, it's a Moto. I'm shopping for one.
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Regards, Karl Shoemaker
To contact me, please visit SRG's web site at
for the current email address.
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Re: Duplexer for amateur 70-cm band
for myself personally those have always worked very well. No issues with desense.?? jonnny? kf6phx
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Anyone know if this is an okay one for 5 MHz spilt? ? I need at least 80db of notch (isolation) Supposedly, it's a Moto. I'm shopping for one.?
--
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Regards, Karl Shoemaker
To contact me, please visit SRG's web site at?
for the current email address.
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Re: Duplexer for amateur 70-cm band
I do know these can be had for much less than the nearly $400.00 I see that one going for. ? Gregg Wardlow 
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From: [email protected] <[email protected]> On Behalf Of Karl Shoemaker via groups.io
Sent: Tuesday, April 8, 2025 12:18 PM
To: [email protected]
Subject: [repeater-builder] Duplexer for amateur 70-cm band? Anyone know if this is an okay one for 5 MHz spilt? ? I need at least 80db of notch (isolation) Supposedly, it's a Moto. I'm shopping for one.? -
Regards, Karl Shoemaker
To contact me, please visit SRG's web site at?
for the current email address.
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Re: Duplexer for amateur 70-cm band
- Anyone know if this is an okay one for 5 MHz spilt? ? I need at least 80db of notch (isolation)
- Supposedly, it's a Moto. I'm shopping for one.?
? I don’t have one to test, I’m a bit suspicious of any duplexer of that design that claims to work across such a wide frequency range (406-500 MHz).? For starters, the interconnect cable lengths would naturally need to be varied across such a wide range to avoid degradation at frequencies far-removed from the optimum center.? Then, the tuning of those resonators is done by loading them at the hot end via slugs.? Generally the more loading, the lower the Q, so I’d be particularly concerned about performance at the low end of the 蝉辫别肠’别诲 range.? If anyone has one of these units surplus and would be willing to loan or sell it, I’ll put it through its paces on the VNA. ? A comparable, and very common, 6-cavity “mobile” UHF duplexer was the RFS/Celwave 633 series.? Those would typically do about 90 dB notch depth when used within its 蝉辫别肠’别诲 range at a 5 MHz split.? RFS used to OEM the 633 for Motorola as well (TDE-7780A was the 450-470 model), but RFS no longer manufacturers them.? ? Attached is a sweep of a 450-470 MHz model 633-6A-2 operating “in band” (GMRS) that should give you an idea of what to expect; I’m not saying that the Motorola/Combilent DSCP10725 will perform the same, just giving you an example of a similar unit.? The ham-band version covered 406-450 MHz (model 633-6A-1), I have a few of those NIB if you want me to sweep one. ? ??????????????????????????????????????????????????????????????????????????????????????????????????????????????? --- Jeff WN3A ?
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Re: Duplexer for amateur 70-cm band
Made by EMR and will do 5MHz split. $75 range would be a better price.?
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Duplexer for amateur 70-cm band
Anyone know if this is an okay one for 5 MHz spilt? ? I need at least 80db of notch (isolation) Supposedly, it's a Moto. I'm shopping for one.?
--
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Regards, Karl Shoemaker
To contact me, please visit SRG's web site at?
for the current email address.
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VHF Cavities and other 220 combining available.... plus MORE
This is a "For What its Worth" post, but maybe it will have some interest.
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I hope posting this here does not violate any group rules, but it seems like the appropriate audience.
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I am clearing out and liquidating a lot of equipment from a closed shop in Las Vegas. Currently I want/need to catalog everything before I start sharing, but in an attempt to save time and shipping expense I am posting the following:
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I have (2) Db Products VHF Combiner racks, (See attached). They stand about 4' high and about 3' square.
(I'm not opposed to parting them out, but initially prefer to see if anyone wants them as? a whole).
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Most of the equipment will most likely be shipped back to the Chicago area to be dealt with, but given the size of these, if anyone is interested in them I would like to know before I screw up the logistics by moving them around.
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As stated, there will be more later, but I also have a LOT of 220 Combining, (Mostly 5 channel racks, but I will part out if necessary), if anyone is interested.
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I also have some of the Securicor 220 repeaters with the PA's as has been discussed. If interested give me a reply (Off Group would be best).
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I am not trying to break anyone's bank on this stuff, but I do have mounting storage and logistical expenses I need to offset, so if anyone is interested, I'm sure we can reach reasonable pricing that benefits both sides.
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Thanks.....
Bob
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PS, As stated, there is a LOT more stuff available that I need to address in ALL bands, (VHF, 220,UHF, 800 & 900), as well as MANY manuals. If you are looking for anything specific, drop me a line, (Off Group) and I'll let you know if I have it.
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I've used TDR to find fault on small JKT(telephone wire) to underground tech cable (10-3)?
The velocity can be anywhere between 50 to 90 % Make sure there is no remaining power connected to any of the wire and I would suggest that you put a known terminating load at the?cable end and make the same test without. This helped me find a lot of strange breaks in the security system cable. And in a oil refinery regulation system.?
Pierre VE2PF
Anyone have experience using a TDR to locate an underground fault for high voltage ?
There's a PUD in central Washing that can't appear to fix an outage for the past three weeks or so.
It's affecting several comm sites and one ski area. It's high up around 7,000 ASL with 20-foot drifts.? The road is derivable around the first or second week of July each season.?
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I'm not sure if it's incompetence or lack of training but the concept seems simple enough to me; send a pulse down the line and watch for the return indicating something is wrong.?
There are several of these units on the market, on line.?
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I also suspect it's not an exact science and requires lots of experience to be effective.?
If I were in the area I suppose I could hook up the (dead) line to a spark plug circuit (from an engine or whatever) and walk the mile line listening for anomalies with an AM radio.?
For now, one leasee is dragging large amounts of propane to keep one site alive.?
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Regards, Karl Shoemaker
To contact me, please visit SRG's web site at?
for the current email address.
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Re: Suggestions for service monitor
Steve, I have RSP Spectrum Analyzer made for the RSP line of inexpensive SDR receivers and while it works well and is cute, its just a toy. Alignment of repeaters which I take as tuning the receiver for best sensitivity, placing it exactly on frequency, measuring the repeater transmitter frequency, measuring transmit deviation, transmit power then possibly sweeping and aligning the duplexer and associated filters and isolator is beyond what a toy SDR could ever do. Amateurs don't have to abide by most FCC specs when placing an amateur repeater on the air but it still takes some accurate and reliable equipment to align all its parts for proper operation. That can be done with a separate frequency measuring device, signal generator, deviation meter and duplexers/filters can certainly be aligned with a CW signal generator and power/millivolt meter or even a diode detector and oscilloscope.?
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When I started in Land Mobile alignment and repair we had mostly separate instruments to perform everything and when I finally got my hands on a Singer FM10C in the 70s I though I had died and gone to heaven. I can't imagine any SDR receiver performing the type of simple tests an old FM10C can do without a host of other expensive equipment to calibrate it or verify if its even within spec. Heck, just the frequency standard in the old FM10C probably cost way more than the BladeRF SDR mentioned. I would recommend getting the best actual radio service monitor that the OP can afford and trade up in the future to a better model. Many good suggestions have been made here but there are also older more affordable models that will work great to get someone started.
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Not for high voltage, but for fire alarm cabling on utility poles.
I had a Riser Bond TDR that I used for fault location.? A long time ago I was asked to find a fault in a municipal cable that was once used for fire alarm call boxes.? The fault was an open circuit.? One of the things that you have to take into consideration is the velocity factor of the cable that you are troubleshooting.? This is usually impossible to know.? So I used another method.? I measured the fault from either end.? Just for a theoretical example, the TDR measurements were 1000 feet and 500 feet.? The actual physical length of the cable was 1000 feet. Interpolating that, the fault was 666 feet from one end and 333 feet from the other.? Sure enough, we found the cable had visible physical damage at this distance and fixed the problem.
I've never done underground TDR testing, but the same method should apply.? If it is a single hard fault (open, short) you should be able to find it.? Multiple faults could be very hard to find.? Be careful of any stray voltage on the cable, as it can damage the test equipment.? We had an Hewlett-Packard TDR test set that was damaged by voltage on the cable.
Joe, K1ike
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On 4/7/2025 11:38 PM, Karl Shoemaker via groups.io wrote: Anyone have experience using a TDR to locate an underground fault for high voltage ?
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Re: Possibly Quintron PA? Need help identifying transistors
Quintron made a lot of equipment for the 72-75Mhz linking band for paging.
Joe, K1ike
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On 4/8/2025 9:00 AM, Jeff DePolo WN3A via groups.io wrote: I’d have to think it’s highband or midband.
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Re: MTR2000 channel steering
Mornin' John,
> I'm trying to program channel steering in the RSS using GPIO
pins on the 96-pin connector without any optional cards.
In the MTR2000, the GPIO pins on J5, the 96-pin System Connector
only connect to J1 and J2, the Option slots in the cardcage.? The
System Controller is at J3.? To use those pins requires an Aux I/O
See the connector table at:
The To/From column shows where the signal connects.
73,
? Dave
On 4/8/2025 6:55 AM, john ni0k wrote:
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Chris,
I'm trying to program channel steering in the RSS using GPIO
pins on the 96-pin connector without any optional cards. That
section of the RSS isn't very straightforward to me.
73
-de "Curly" John NI0K
call me: 6100271
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Attached is some information on the DB212 antennas.? Perhaps this will help.? This was factory info from a DB212-2 that was tuned to 47.14 MHz. 73 Joe WB4HIS ?
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From: [email protected] [mailto:[email protected]] On Behalf Of Roger willey via groups.io
Sent: Tuesday, April 8, 2025 09:28
To: [email protected]
Cc: [email protected]
Subject: Re: [repeater-builder] 6 m repeater antenna? ?
On Apr 7, 2025, at 5:55?PM, wgwl via groups.io <wgwl@...> wrote: ? Roger,
In hopes of answering your original question, I got my hands on a DB212-2 originally on 37.7MHz and shortened the antennas and matching section for 6?
meters. The 35 ohm matching section (Decibel Products VB-83 cable) was shortened?
to 36.25" end to end. With a UHF T on the end?
and two 50 ohm loads attached resulted in the attached plot. As you can see, the?
exact length is not critical across the band. John,
You mentioned "DB factory lengths" in an earlier post. Do you have access to the?
actual factory length chart for 6M ? If so, please share. How well did the tuning of your antenna on the ground translate to mounting on a tower? What length of pipe did you use when tuning? <6meter DB212-2 matching section.png>
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Kevin Custer
Gregg
Karl Shoemaker
Pierre Martel
Dave WA1JHK