[Milsurplus] [Boatanchors] CU-872A/U antenna coupler FS near Boston

Thu Feb 21 11:04:23 EST 2019

Multi couplers are for receivers, and isn’t the optimum coax impedance around 70 ohms for signal loss?  The optimum for power transmission is closer to 50 ohms IIRC. These were made some time ago, perhaps before 50 ohms was settled on as the standard for radio gear except CATV systems. Just trying to think out loud why those things were 70 ohms. 

Peter

> On Feb 21, 2019, at 10:56 AM, Francesco Ledda <frledda at att.net> wrote:
> 
> I understand the mismatch and its engineering implications.
>  
> My question is why would anybody design mismatch in the system.  Most transmitters used an antenna coupler anyway.
>  
> From: milsurplus-bounces at mailman.qth.net <milsurplus-bounces at mailman.qth.net> On Behalf Of Jim Whartenby
> Sent: Wednesday, February 20, 2019 10:53 PM
> To: Francesco Ledda <frledda at att.net>
> Cc: MilSurplus QSLNet <milsurplus at mailman.qth.net>
> Subject: Re: [Milsurplus] [Boatanchors] CU-872A/U antenna coupler FS near Boston
>  
> Frank asked: "Wonder why?"
>  
> Most likely since at HF, the impedance mismatch is pretty much insignificant, especially if one considers the length of the coax run from antenna to RX.  https://www.pasternack.com/images/ProductPDF/RG8A-U.pdf 
> So about 1 dB loss at 30 mc per 100 feet or 0.2 db loss at 1 mc per 100 feet.
>  
> From: http://wc7i.com/Vertical%20Antenna%20Conclusions.htm
>  
> Z of a vertical antenna is about 36 ohms, Z of horizontal antenna is about 72 ohms, both give a 1.4:1 VSWR.  The VSWR from mating a 50 to 75 ohm coax is 1.5:1  In all of the above cases, the load mismatch attenuation is under 0.2 dB
>  
> Comparing UHF connectors to most modern connectors is also interesting.  I myself wonder why the the UHF connector is still used?
> See: https://www.hamradio.me/connectors/uhf-connector-test-results.html for connector comparisons from SMA to UHF.
> Regards,
> Jim
>  
> I wonder why people argue over the 10% of their differences and ignore the 90% they agree on?
>  
>  
> On Wednesday, February 20, 2019, 6:09:03 PM CST, Francesco Ledda <frledda at att.net> wrote:
>  
>  
> Also, the CU-1099/FRR is 70 ohm. It was used with receivers with Z 50 ohm.  Wonder why....
> 
> Sent from my iPad
> 
> On Feb 20, 2019, at 17:50, W2HX <w2hx at w2hx.com> wrote:
> 
> Probably the gain in the unit compensated for any losses due to impedance mismatch
>  
> Sent from Nine
> From: Nick England <navy.radio at gmail.com>
> Sent: Wednesday, February 20, 2019 5:00 PM
> To: W2HX
> Cc: MilSurplus QSLNet; r-390 at mailman.qth.net; John Flood
> Subject: Re: [Milsurplus] [Boatanchors] CU-872A/U antenna coupler FS near Boston
>  
> The parts list says it has UG-58A/U connectors. Everything I can find says that is a 50 ohm connector.
> I think all the military type N listings are 50 ohm.
> Nick England K4NYW
> www.navy-radio.com
>  
>  
> On Wed, Feb 20, 2019 at 2:56 PM W2HX <w2hx at w2hxcom> wrote:
> John et al., 
> 
> This is an interesting multicoupler. One interesting thing I've wondered about...It has a 70 ohm antenna matching input impedance. And i always wondered if the antenna connector was a 75 ohm N connector or the standard 50 ohm (The difference is that the male center pin is thicker on the 50 ohm version, and will damage a 75 ohm female part)
> Just something to look out for.
> 
> Wikipedia has a nice photo of both impedances and genders.
> 
> 73 Eugene W2HX
> 
> ________________________________________
> From: boatanchors-bounces at mailman.qth.net <boatanchors-bounces at mailman.qth.net> on behalf of John Flood via Boatanchors <boatanchors at mailman.qth.net>
> Sent: Wednesday, February 20, 2019 1:24 PM
> To: MilSurplus QSLNet; r-390 at mailman.qth.net; BOATANCHORS2 LIST
> Subject: [Boatanchors] CU-872A/U antenna coupler FS near Boston
> 
> Greetings,
> This is working, some "test" readings are a bit on the low side so perhaps some of the 6922 tubes are getting tired.  There is some glue residue below the normal data tag most likely from some other data tag that was mounted there.  Looking for a local sale in the Metrowest or North Shore Boston (This of course means that the first reply will come from Alaska!).  I'm not really interested in shipping this or dealing with Paypal any more in MA.  Any interest?  I could bring it to the Lewiston ME, Nashua, NH, or Framingham, MA fleas.  Nearfest as well but I hope it finds a home sooner than May!
> John Flood N1JAF978-979-2807
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