Performance of tube recievers on higher bands.

[WA1GFZ]

Good VSWR has nothing to do with insertion loss.
I bet 100 feet of RG58 has great VSWR on 2 meters.

[ke7trp]

I guess you dont trust the Belden ratings for 20 and 30 mhz then?  its less then a DB for a 100Ft no matter who makes the cable.

C

[WD5JKO]

A few things you need to consider when operating 15 and 10 meters.
3. The feed line loss can be an issue
You really need double shielded cable like RG223, RG142, RG400.
I can copy strong stations on 75 by the leakage of single shielded cable between my generator and test RX.  

  Those coax cables you mention are all fine coax with a double shield. They are however high loss cables for a long run. I'd only use them for short patch cord runs in the shack, and use another type of low loss cable to the antenna such as RG-214, or LMR400:

Type       Loss DB / 100' at 21.4 Mhz  % efficiency
RG-142    1.73                                 67.2
RG-223    1.8                                   66
RG-400    2.0                                   63
RG-214    1.0                                   79.8
LMR-400   .57                                  87.7

RG-214 is also a double shielded cable like its older cousin RG-9b
LMR-400: RF Shielding is 50 dB greater than typical single
shielded coax (40 dB). The multi-ply bonded foil outer
conductor is rated conservatively at > 90 dB

DB Loss Calculator:
http://www.timesmicrowave.com/cgi-bin/calculate.pl

LMR-400:
http://www.timesmicrowave.com/products/lmr/downloads/22-25.pdf

Jim
WD5JKO

[KM1H]

The double shield suggestion was for connecting to the signal generator. I use Belden 9907 which is a RG-58 style developed for an early Ethernet application; found a 500' roll of the stuff at a yard sale for $5. Very flexible compared to the RG-142B I had been using.  The HP-606A I use had plenty of leakage after knocking around for 50 years and took some effort to minimize and is now at or below the 8640B. Cables and external lab grade switchable attenuators are leak free at signal levels used. What data I record is accurate.

I automatically question very low MDS claims without knowing all the setup details and for AM a MDS is almost useless since receivers have a wide range of being able to actually convert a signal to useable audio. MDS also has no absolute definition which can vary from the ears ability to say "I think I heard something" to a 3dB difference on the output meter. I use a 10dB SNR as the measurement standard here for AM since even poor receivers can usually meet that.

The prior statement that if the noise goes up with the antenna connected the sensitivity is good enough has been disproven many times. It held value when initially stated in the 30's or so and as receiver technology advanced it became less true.
Band noise is highly variable, directional, and random; only sun noise is a constant and for HF not an issue. The human ear can copy CW and SSB below that noise and integrate it into intelligence; the bigger the difference between receiver and band noise (with the receiver noise the lowest of course) the better chance of deciphering it. Some digital modes are limited only by the receivers ultimate MDS and are relentless and very patient.

Now for those on here with an interest in only low band AM and mostly vintage receivers all of this is moot but for those who enjoy 10M and/or other bands/modes with the latest and greatest or upgraded tube gear it is significant.

Carl

[ke7trp]

Jim, Brand not type. 100ft of Coax is not used on the test bench. My cable is less then a db at 100ft. I have less then 100 ft.  The subject is low performance of tube recievers on the higher bands not not coax loss. He was sugesting lossy coax as a reason for lower performance up on the high bands which is not the case.

I tested the 75a4 for fun. It came in at .28 mv for min signal. S9 for 50mv kn 15 meters.  On 10 meters things fall off. V3ery usable on the 15. So so on 10.

[Jim, W5JO]

No one suggested that loss in the coax was a problem.  The suggestion was integrity of the test equipment and connecting cables.  As Frank pointed out, there is a difference.

[ke7trp]

Jim.. You obviously did not read his post. I will quote it here:

"MDS of .3uv is not bad on 10 meters but if you have 3 or more db of coax loss that could be YOUR PROBLEM. "

I explained that my coax has less then a DB loss for 100 FT.  2 ft of it has no measurable loss to speak of. For some reason you felt it would help by listing out types of Coax and loss ratings for 100Ft.

Clear now?

C

[WD5JKO]

Clear now?
C

  Yes Clark, I was keyed off the general statement Frank made that was not specific to your station:

"3. The feed line loss can be an issue"

He did recommend some very nice coax's, but I did not realize he meant them to be used between an RF signal Gen and Receiver.

Jim
WD5JKO

[ke7trp]

Yes. It was confusing.  The coax issue makes great sense.  I have used new high quality coax though. 

On 15 meters now at 21.430.  We are due a storm but I hope I can make some contacts today!

C

[KM1H]

No one suggested that loss in the coax was a problem.


Jim.. You obviously did not read his post.

 

[Jim, W5JO]

No one suggested that loss in the coax was a problem.


Jim.. You obviously did not read his post.

 

Haven't we been through this recently?   

[WD5JKO]

  I have used new high quality coax though. 

  Just curious which type of coax you are using? You stated it was Beldon, but unless I missed it, the type was not specified.

Jim
WD5JKO

[ke7trp]

Where Jim? I have different types.
C

[WD5JKO]

Where Jim? I have different types.
C

Clark,  I was referring to the long run from the shack to the beam up the tower. Also curious on your opinion of one type or the other that you have used.

Earlier in this thread Carl was referring to receiver sensitivity in the presence of the antenna background noise. Made me think about possible feedline pickup, and antenna imbalance where the receiver performance might be degraded. The coax used even if low loss might have other characteristics that can degrade receiver performance.

Something we never talk about too is coax terminations with the beloved PL-259. I recall Ozona Bob, W5PYT (SK) who had many exotic antennas. Bob once told me that he NEVER soldered the coax braid in the PL-259!

  I don't have many high performance receivers here, but I recall my old Yaesu FT-757 was quite hard of hearing on 15-10m whereas my SP-600 heard signals Q5 that were not detectable on the 757. My Gonset G-50 is the same way over my Icom R-75 on 6M. The Icom R-75 however on 75M performs admirably when my neighbor (100 yards away) is 20KC away running SSB with his amplifier. The SP-600 rolls over dead when this happens.

  A few weeks ago I heard you briefly on 15m AM, and you were strong. I think the propagation between here and there is a little too close normally.


Jim
wD5JKO

[ke7trp]

On the tower to the beam I am using DX engineering coax.  One run straight to the radio.

http://www.dxengineering.com/Parts.asp?ID=5399&PLID=373&SecID=127&DeptID={7C0A8FE1-F72C-4346-916E-8AA93CD2A66B}&PartNo=DXE%2D400MAXDU100


DXE-400MAX cable is protected by a special polyethylene (PE) jacket and is recommended for both indoor and outdoor applications and direct burial.  The PE jacket assures long life where ultraviolet contamination is a concern.

DXE-400MAX has a flexible 10 gauge stranded copper center, polyethylene dielectric, bonded foil plus 96% coverage bare copper shield and a PE jacket.   

DX Engineering Premium Grade cable assemblies are built with high quality Silver/Teflon® crimp/solder PL-259 (UHF) installed at each end.

An adhesive lined shrink tubing is used to form a weather-resistant bond between the connector body and the coax.   Each assembly is then 100% Hi-Pot high voltage tested to guarantee a quality cable assembly you can count on.

C