John – can you elaborate? ? ?
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From: [email protected] <[email protected]> On Behalf Of John N3XKD via groups.io
Sent: Tuesday, April 8, 2025 9:37 PM
To: [email protected]
Subject: Re: [repeater-builder] UHF mobiles? TK-890's aren't bad, but some need slight tweaking ? I have a Harris XG-75M that does 440-512 stock. Got it off eBay for about $175. Excellent radio with lots of features.?
--
The line separating good and evil passes not through states, nor between classes, nor between political parties either—but right through every human heart—and through all human hearts. This line shifts. Inside us, it oscillates with the years. And even within hearts overwhelmed by evil, one small bridgehead of good is retained. And even in the best of all hearts, there remains … an unuprooted small corner of evil. - Aleksandr Solzhenitsyn
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Re: TX Board for Motorola XPR8300 Repeater?
I did the same with great success. Also added a ~2" muffin fan to the additional tx deck heatsink. Been working well through thousands of daily nets for close to 10 years.
Ross? kc7rjk
On Apr 8, 2025 1:38 PM, "Chris Boone WB5ITT via groups.io" <setxtelecom@...> wrote: Swap the TX and RX decks...replace the piss poor fabric under the heatsink on the TX..use artic silver....run power lower at 30 instead of 40watts ..
Chris WB5ITT
I am resurrecting an XPR8300. The TX board is scorched.?
?
Board #:
MOTOTRBO U1-HP
8486777Z14-C
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UHF Ham Range
?
Does anyone have a parted-out XPR8300 willing to sell the TX board to me?
?
The poor heat-dissipation design makes this a seemingly common ailment.
?
Private message me.
?
Thanks,
?
Steve, N9ATO
?
?
?
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TK-890's aren't bad, but some need slight tweaking
I have a Harris XG-75M that does 440-512 stock. Got it off eBay for about $175. Excellent radio with lots of features.?
-- John Kreno
The line separating good and evil passes not through states, nor between classes, nor between political parties either—but right through every human heart—and through all human hearts. This line shifts. Inside us, it oscillates with the years. And even within hearts overwhelmed by evil, one small bridgehead of good is retained. And even in the best of all hearts, there remains … an unuprooted small corner of evil. - Aleksandr Solzhenitsyn
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Follow up on KMC 35 Mic Mod for TKX90 Radios
For anyone not reading our original post a little background. The repeater-builder article on the TK690H mentioned that the black KMC35 mic gave better sounding audio than the OEM grey KMC27 mic supplied with the radio. This is noticeably the case, but there seemed to me that a little more highs would be an improvement even on the KMC35 mike replacement, which is the OEM mike supplied with the TK8180 and some other Kenwood mobiles. Therefore I removed chip cap C10 on the mic pc board which works as a low level low pass filter in the 600 ohm mic input to the radio to partially cut off above about 2200-2500 cps. The result was a somewhat improvement in passing some more speech highs, with no noticeable effect on mike lows, so probably? worth removing 0.068 uF C10.? The comment was made that that should not be necessary as audio was quite good with the KMC35 mike as stock. Then I realized that the TK8180 audio input response is flat to 2800 cps, but only to about 2200-2500 cps on the TK690H? radios tested.?
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John
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I have a Harris XG-75M that does 440-512 stock. Got it off eBay for about $175. Excellent radio with lots of features.?
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I've had good luck with Icom 6061?
Mike Ka2ndw
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On Tue, April 8, 2025 5:38
pm, Chad Nelson wrote:
Hi,
?
Does anyone know what
version 2 UHF radios in the commercial line will operate
440-470 straight through without retuning?
?
I have the TK 8180 which
works great in that range, the TK 8302 needs tweaking
every couple of MHz.
?
Interested to know what
other radios will do this that have a front mounted
speaker?
?
~Thanks,
?
Chad
?
?
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Hi, ? Does anyone know what version 2 UHF radios in the commercial line will operate 440-470 straight through without retuning? ? I have the TK 8180 which works great in that range, the TK 8302 needs tweaking every couple of MHz. ? Interested to know what other radios will do this that have a front mounted speaker? ? ~Thanks, ? Chad
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Re: Duplexer for amateur 70-cm band
Yep...I have several myself...I can part with one if need be
Chris WB5ITT
If you can make it to Dayton in May there will be lots of those duplexers there cheap. Last few I bought were under $50 and they work fine.?
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Re: Improving selectivity on a reciver
The schematic for the receiver in question shows a single broad band pass filter before the FET 1st amplifier then a three section helical resonator after that. Not a very good design which would rely on the duplexer band pass to protect the FET from overload, generating IMD, etc. Depending on the duplexer used a single 1/4 wave cavity filter ahead of the receiver module would go a long way to reduce the repeater transmitter or out of band signals from degrading receive.?
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Re: Duplexer for amateur 70-cm band
If you can make it to Dayton in May there will be lots of those duplexers there cheap. Last few I bought were under $50 and they work fine.?
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Re: TX Board for Motorola XPR8300 Repeater?
Swap the TX and RX decks...replace the piss poor fabric under the heatsink on the TX..use artic silver....run power lower at 30 instead of 40watts ..
Chris WB5ITT
I am resurrecting an XPR8300. The TX board is scorched.?
?
Board #:
MOTOTRBO U1-HP
8486777Z14-C
?
UHF Ham Range
?
Does anyone have a parted-out XPR8300 willing to sell the TX board to me?
?
The poor heat-dissipation design makes this a seemingly common ailment.
?
Private message me.
?
Thanks,
?
Steve, N9ATO
?
?
?
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Re: Duplexer for amateur 70-cm band
Yup, Jeff, that was my suspecition as well; reason I reached out.? Thanks guys for the input. I'll keep looking. It's for our new fusion repeater at a site that has little population in these bands. It's mainly an ISP site. Untill we get better funds and buy a real duplexer, BpBr, etc.
--
-
Regards, Karl Shoemaker
To contact me, please visit SRG's web site at?
for the current email address.
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TX Board for Motorola XPR8300 Repeater?
I am resurrecting an XPR8300. The TX board is scorched.?
?
Board #:
MOTOTRBO U1-HP
8486777Z14-C
?
UHF Ham Range
?
Does anyone have a parted-out XPR8300 willing to sell the TX board to me?
?
The poor heat-dissipation design makes this a seemingly common ailment.
?
Private message me.
?
Thanks,
?
Steve, N9ATO
?
?
?
|
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?
|
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.? ?
?
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.
--
-
Regards, Karl Shoemaker
To contact me, please visit SRG's web site at
for the current email address.
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Mike Besemer - WM4B
Chris Boone WB5ITT
Karl Shoemaker
Kevin Custer